VFS: add FMODE_CAN_ODIRECT file flag

Currently various places test if direct IO is possible on a file by
checking for the existence of the direct_IO address space operation.
This is a poor choice, as the direct_IO operation may not be used - it is
only used if the generic_file_*_iter functions are called for direct IO
and some filesystems - particularly NFS - don't do this.

Instead, introduce a new f_mode flag: FMODE_CAN_ODIRECT and change the
various places to check this (avoiding pointer dereferences).
do_dentry_open() will set this flag if ->direct_IO is present, so
filesystems do not need to be changed.

NFS *is* changed, to set the flag explicitly and discard the direct_IO
entry in the address_space_operations for files.

Other filesystems which currently use noop_direct_IO could usefully be
changed to set this flag instead.

Link: https://lkml.kernel.org/r/164859778128.29473.15189737957277399416.stgit@noble.brown
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: NeilBrown <neilb@suse.de>
Tested-by: David Howells <dhowells@redhat.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

MM: handle THP in swap_*page_fs() - count_vm_events()

We need to use count_swpout_vm_event() for sio_write_complete() to get
correct counting.

Note that THP swap in (if it ever happens) is current accounted 1 for each
page, whether HUGE or normal.  This is different from swap-out accounting.

This patch should be squashed into
    MM: handle THP in swap_*page_fs()

Link: https://lkml.kernel.org/r/165146948934.24404.5909750610552745025@noble.neil.brown.name
Signed-off-by: NeilBrown <neilb@suse.de>
Reported-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Huang Ying <ying.huang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: handle THP in swap_*page_fs()

Pages passed to swap_readpage()/swap_writepage() are not necessarily all
the same size - there may be transparent-huge-pages involves.

The BIO paths of swap_*page() handle this correctly, but the SWP_FS_OPS
path does not.

So we need to use thp_size() to find the size, not just assume PAGE_SIZE,
and we need to track the total length of the request, not just assume it
is "page * PAGE_SIZE".

Link: https://lkml.kernel.org/r/165119301488.15698.9457662928942765453.stgit@noble.brown
Signed-off-by: NeilBrown <neilb@suse.de>
Reported-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: submit multipage write for SWP_FS_OPS swap-space

swap_writepage() is given one page at a time, but may be called repeatedly
in succession.

For block-device swapspace, the blk_plug functionality allows the multiple
pages to be combined together at lower layers.  That cannot be used for
SWP_FS_OPS as blk_plug may not exist - it is only active when
CONFIG_BLOCK=y.  Consequently all swap reads over NFS are single page
reads.

With this patch we pass a pointer-to-pointer via the wbc.  swap_writepage
can store state between calls - much like the pointer passed explicitly to
swap_readpage.  After calling swap_writepage() some number of times, the
state will be passed to swap_write_unplug() which can submit the combined
request.

Link: https://lkml.kernel.org/r/164859778128.29473.5191868522654408537.stgit@noble.brown
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: David Howells <dhowells@redhat.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: submit multipage reads for SWP_FS_OPS swap-space

swap_readpage() is given one page at a time, but may be called repeatedly
in succession.

For block-device swap-space, the blk_plug functionality allows the
multiple pages to be combined together at lower layers.  That cannot be
used for SWP_FS_OPS as blk_plug may not exist - it is only active when
CONFIG_BLOCK=y.  Consequently all swap reads over NFS are single page
reads.

With this patch we pass in a pointer-to-pointer when swap_readpage can
store state between calls - much like the effect of blk_plug.  After
calling swap_readpage() some number of times, the state will be passed to
swap_read_unplug() which can submit the combined request.

Link: https://lkml.kernel.org/r/164859778127.29473.14059420492644907783.stgit@noble.brown
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: David Howells <dhowells@redhat.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

doc: update documentation for swap_activate and swap_rw

This documentation for ->swap_activate() has been out-of-date for a long
time.  This patch updates it to match recent changes, and adds
documentation for the associated ->swap_rw()

Link: https://lkml.kernel.org/r/164859778126.29473.6778751233552859461.stgit@noble.brown
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: David Howells <dhowells@redhat.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: perform async writes to SWP_FS_OPS swap-space using ->swap_rw

This patch switches swap-out to SWP_FS_OPS swap-spaces to use ->swap_rw
and makes the writes asynchronous, like they are for other swap spaces.

To make it async we need to allocate the kiocb struct from a mempool.
This may block, but won't block as long as waiting for the write to
complete.  At most it will wait for some previous swap IO to complete.

Link: https://lkml.kernel.org/r/164859778126.29473.12399585304843922231.stgit@noble.brown
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: David Howells <dhowells@redhat.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

nfs: rename nfs_direct_IO and use as ->swap_rw

The nfs_direct_IO() exists to support SWAP IO, but hasn't worked for a
while.  We now need a ->swap_rw function which behaves slightly
differently, returning zero for success rather than a byte count.

So modify nfs_direct_IO accordingly, rename it, and use it as the
->swap_rw function.

Link: https://lkml.kernel.org/r/165119301493.15698.7491285551903597618.stgit@noble.brown
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be> (on Renesas RSK+RZA1 with 32 MiB of SDRAM)
Cc: David Howells <dhowells@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: introduce ->swap_rw and use it for reads from SWP_FS_OPS swap-space

swap currently uses ->readpage to read swap pages.  This can only request
one page at a time from the filesystem, which is not most efficient.

swap uses ->direct_IO for writes which while this is adequate is an
inappropriate over-loading.  ->direct_IO may need to had handle allocate
space for holes or other details that are not relevant for swap.

So this patch introduces a new address_space operation: ->swap_rw.  In
this patch it is used for reads, and a subsequent patch will switch writes
to use it.

No filesystem yet supports ->swap_rw, but that is not a problem because
no filesystem actually works with filesystem-based swap.
Only two filesystems set SWP_FS_OPS:
- cifs sets the flag, but ->direct_IO always fails so swap cannot work.
- nfs sets the flag, but ->direct_IO calls generic_write_checks()
  which has failed on swap files for several releases.

To ensure that a NULL ->swap_rw isn't called, ->activate_swap() for both
NFS and cifs are changed to fail if ->swap_rw is not set.  This can be
removed if/when the function is added.

Future patches will restore swap-over-NFS functionality.

To submit an async read with ->swap_rw() we need to allocate a structure
to hold the kiocb and other details.  swap_readpage() cannot handle
transient failure, so we create a mempool to provide the structures.

Link: https://lkml.kernel.org/r/164859778125.29473.13430559328221330589.stgit@noble.brown
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: David Howells <dhowells@redhat.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: reclaim mustn't enter FS for SWP_FS_OPS swap-space

If swap-out is using filesystem operations (SWP_FS_OPS), then it is not
safe to enter the FS for reclaim.  So only down-grade the requirement for
swap pages to __GFP_IO after checking that SWP_FS_OPS are not being used.

This makes the calculation of "may_enter_fs" slightly more complex, so
move it into a separate function.  with that done, there is little value
in maintaining the bool variable any more.  So replace the may_enter_fs
variable with a may_enter_fs() function.  This removes any risk for the
variable becoming out-of-date.

Link: https://lkml.kernel.org/r/164859778124.29473.16176717935781721855.stgit@noble.brown
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: David Howells <dhowells@redhat.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: move responsibility for setting SWP_FS_OPS to ->swap_activate

If a filesystem wishes to handle all swap IO itself (via ->direct_IO and
->readpage), rather than just providing devices addresses for
submit_bio(), SWP_FS_OPS must be set.

Currently the protocol for setting this it to have ->swap_activate return
zero.  In that case SWP_FS_OPS is set, and add_swap_extent() is called for
the entire file.

This is a little clumsy as different return values for ->swap_activate
have quite different meanings, and it makes it hard to search for which
filesystems require SWP_FS_OPS to be set.

So remove the special meaning of a zero return, and require the filesystem
to set SWP_FS_OPS if it so desires, and to always call add_swap_extent()
as required.

Currently only NFS and CIFS return zero for add_swap_extent().

Link: https://lkml.kernel.org/r/164859778123.29473.17908205846599043598.stgit@noble.brown
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: David Howells <dhowells@redhat.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: drop swap_dirty_folio

folios that are written to swap are owned by the MM subsystem - not any
filesystem.

When such a folio is passed to a filesystem to be written out to a
swap-file, the filesystem handles the data, but the folio itself does not
belong to the filesystem.  So calling the filesystem's ->dirty_folio()
address_space operation makes no sense.  This is for folios in the given
address space, and a folio to be written to swap does not exist in the
given address space.

So drop swap_dirty_folio() which calls the address-space's
->dirty_folio(), and always use noop_dirty_folio(), which is appropriate
for folios being swapped out.

Link: https://lkml.kernel.org/r/164859778123.29473.6900942583784889976.stgit@noble.brown
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: David Howells <dhowells@redhat.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: create new mm/swap.h header file

Patch series "MM changes to improve swap-over-NFS support".

Assorted improvements for swap-via-filesystem.

This is a resend of these patches, rebased on current HEAD.  The only
substantial changes is that swap_dirty_folio has replaced
swap_set_page_dirty.

Currently swap-via-fs (SWP_FS_OPS) doesn't work for any filesystem.  It
has previously worked for NFS but that broke a few releases back.  This
series changes to use a new ->swap_rw rather than ->readpage and
->direct_IO.  It also makes other improvements.

There is a companion series already in linux-next which fixes various
issues with NFS.  Once both series land, a final patch is needed which
changes NFS over to use ->swap_rw.

This patch (of 10):

Many functions declared in include/linux/swap.h are only used within mm/

Create a new "mm/swap.h" and move some of these declarations there.
Remove the redundant 'extern' from the function declarations.

[akpm@linux-foundation.org: mm/memory-failure.c needs mm/swap.h]
Link: https://lkml.kernel.org/r/164859751830.29473.5309689752169286816.stgit@noble.brown
Link: https://lkml.kernel.org/r/164859778120.29473.11725907882296224053.stgit@noble.brown
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: David Howells <dhowells@redhat.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

selftests: clarify common error when running gup_test

The gup_test binary will fail showing only the output of perror("open") in
the case that /sys/kernel/debug/gup_test is not found. This will almost
always be due to CONFIG_GUP_TEST not being set, which enables
compilation of a kernel that provides this file.

Add a short error message to clarify this failure and point the user to
the solution.

Link: https://lkml.kernel.org/r/20220502224942.995427-1-jsavitz@redhat.com
Signed-off-by: Joel Savitz <jsavitz@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Nico Pache <npache@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/gup: fix comments to pin_user_pages_*()

pin_user_pages API forces FOLL_PIN in gup_flags, which means that the API
requires struct page **pages to be provided (not NULL).  However, the
comment to pin_user_pages() clearly allows for passing in a NULL @pages
argument.

Remove the incorrect comments, and add WARN_ON_ONCE(!pages) calls to
enforce the API.

It has been independently spotted by Minchan Kim and confirmed with
John Hubbard:

https://lore.kernel.org/all/YgWA0ghrrzHONehH@google.com/

Link: https://lkml.kernel.org/r/20220422015839.1274328-1-yury.norov@gmail.com
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

powerpc/pgtable: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE for book3s

Right now, the last 5 bits (0x1f) of the swap entry are used for the type
and the bit before that (0x20) is used for _PAGE_SWP_SOFT_DIRTY.  We
cannot use 0x40, as that collides with _RPAGE_RSV1 -- contained in
_PAGE_HPTEFLAGS.  The next candidate would be _RPAGE_SW3 (0x200) -- which
is used for _PAGE_SOFT_DIRTY for !swp ptes.

So let's just use _PAGE_SOFT_DIRTY for _PAGE_SWP_SOFT_DIRTY (to make it
easier to grasp) and use 0x20 now for _PAGE_SWP_EXCLUSIVE.

Link: https://lkml.kernel.org/r/20220329164329.208407-9-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

powerpc/pgtable: remove _PAGE_BIT_SWAP_TYPE for book3s

The swap type is simply stored in bits 0x1f of the swap pte.  Let's
simplify by just getting rid of _PAGE_BIT_SWAP_TYPE.  It's not like that
we can simply change it: _PAGE_SWP_SOFT_DIRTY would suddenly fall into
_RPAGE_RSV1, which isn't possible and would make the
BUILD_BUG_ON(_PAGE_HPTEFLAGS & _PAGE_SWP_SOFT_DIRTY) angry.

While at it, make it clearer which bit we're actually using for
_PAGE_SWP_SOFT_DIRTY by just using the proper define and introduce and use
SWP_TYPE_MASK.

Link: https://lkml.kernel.org/r/20220329164329.208407-8-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

s390/pgtable: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE

Let's use bit 52, which is unused.

Link: https://lkml.kernel.org/r/20220329164329.208407-7-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

s390/pgtable: cleanup description of swp pte layout

Bit 52 and bit 55 don't have to be zero: they only trigger a
translation-specifiation exception if the PTE is marked as valid, which is
not the case for swap ptes.

Document which bits are used for what, and which ones are unused.

Link: https://lkml.kernel.org/r/20220329164329.208407-6-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arm64/pgtable: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE

Let's use one of the type bits: core-mm only supports 5, so there is no
need to consume 6.

Note that we might be able to reuse bit 1, but reusing bit 1 turned out
problematic in the past for PROT_NONE handling; so let's play safe and use
another bit.

Link: https://lkml.kernel.org/r/20220329164329.208407-5-david@redhat.com
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

x86/pgtable: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE

Let's use bit 3 to remember PG_anon_exclusive in swap ptes.

[david@redhat.com: fix 32-bit swap layout]
Link: https://lkml.kernel.org/r/d875c292-46b3-f281-65ae-71d0b0c6f592@redhat.com
Link: https://lkml.kernel.org/r/20220329164329.208407-4-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/debug_vm_pgtable: add tests for __HAVE_ARCH_PTE_SWP_EXCLUSIVE

Let's test that __HAVE_ARCH_PTE_SWP_EXCLUSIVE works as expected.

Link: https://lkml.kernel.org/r/20220329164329.208407-3-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/swap: remember PG_anon_exclusive via a swp pte bit

Patch series "mm: COW fixes part 3: reliable GUP R/W FOLL_GET of anonymous pages", v2.

This series fixes memory corruptions when a GUP R/W reference (FOLL_WRITE
| FOLL_GET) was taken on an anonymous page and COW logic fails to detect
exclusivity of the page to then replacing the anonymous page by a copy in
the page table: The GUP reference lost synchronicity with the pages mapped
into the page tables.  This series focuses on x86, arm64, s390x and
ppc64/book3s -- other architectures are fairly easy to support by
implementing __HAVE_ARCH_PTE_SWP_EXCLUSIVE.

This primarily fixes the O_DIRECT memory corruptions that can happen on
concurrent swapout, whereby we lose DMA reads to a page (modifying the
user page by writing to it).

O_DIRECT currently uses FOLL_GET for short-term (!FOLL_LONGTERM) DMA
from/to a user page.  In the long run, we want to convert it to properly
use FOLL_PIN, and John is working on it, but that might take a while and
might not be easy to backport.  In the meantime, let's restore what used
to work before we started modifying our COW logic: make R/W FOLL_GET
references reliable as long as there is no fork() after GUP involved.

This is just the natural follow-up of part 2, that will also further
reduce "wrong COW" on the swapin path, for example, when we cannot remove
a page from the swapcache due to concurrent writeback, or if we have two
threads faulting on the same swapped-out page.  Fixing O_DIRECT is just a
nice side-product

This issue, including other related COW issues, has been summarized in [3]
under 2):
"
  2. Intra Process Memory Corruptions due to Wrong COW (FOLL_GET)

  It was discovered that we can create a memory corruption by reading a
  file via O_DIRECT to a part (e.g., first 512 bytes) of a page,
  concurrently writing to an unrelated part (e.g., last byte) of the same
  page, and concurrently write-protecting the page via clear_refs
  SOFTDIRTY tracking [6].

  For the reproducer, the issue is that O_DIRECT grabs a reference of the
  target page (via FOLL_GET) and clear_refs write-protects the relevant
  page table entry. On successive write access to the page from the
  process itself, we wrongly COW the page when resolving the write fault,
  resulting in a loss of synchronicity and consequently a memory corruption.

  While some people might think that using clear_refs in this combination
  is a corner cases, it turns out to be a more generic problem unfortunately.

  For example, it was just recently discovered that we can similarly
  create a memory corruption without clear_refs, simply by concurrently
  swapping out the buffer pages [7]. Note that we nowadays even use the
  swap infrastructure in Linux without an actual swap disk/partition: the
  prime example is zram which is enabled as default under Fedora [10].

  The root issue is that a write-fault on a page that has additional
  references results in a COW and thereby a loss of synchronicity
  and consequently a memory corruption if two parties believe they are
  referencing the same page.
"

We don't particularly care about R/O FOLL_GET references: they were never
reliable and O_DIRECT doesn't expect to observe modifications from a page
after DMA was started.

Note that:
* this only fixes the issue on x86, arm64, s390x and ppc64/book3s
  ("enterprise architectures"). Other architectures have to implement
  __HAVE_ARCH_PTE_SWP_EXCLUSIVE to achieve the same.
* this does *not * consider any kind of fork() after taking the reference:
  fork() after GUP never worked reliably with FOLL_GET.
* Not losing PG_anon_exclusive during swapout was the last remaining
  piece. KSM already makes sure that there are no other references on
  a page before considering it for sharing. Page migration maintains
  PG_anon_exclusive and simply fails when there are additional references
  (freezing the refcount fails). Only swapout code dropped the
  PG_anon_exclusive flag because it requires more work to remember +
  restore it.

With this series in place, most COW issues of [3] are fixed on said
architectures. Other architectures can implement
__HAVE_ARCH_PTE_SWP_EXCLUSIVE fairly easily.

[1] https://lkml.kernel.org/r/20220329160440.193848-1-david@redhat.com
[2] https://lkml.kernel.org/r/20211217113049.23850-1-david@redhat.com
[3] https://lore.kernel.org/r/3ae33b08-d9ef-f846-56fb-645e3b9b4c66@redhat.com

This patch (of 8):

Currently, we clear PG_anon_exclusive in try_to_unmap() and forget about
it.  We do this, to keep fork() logic on swap entries easy and efficient:
for example, if we wouldn't clear it when unmapping, we'd have to lookup
the page in the swapcache for each and every swap entry during fork() and
clear PG_anon_exclusive if set.

Instead, we want to store that information directly in the swap pte,
protected by the page table lock, similarly to how we handle
SWP_MIGRATION_READ_EXCLUSIVE for migration entries.  However, for actual
swap entries, we don't want to mess with the swap type (e.g., still one
bit) because it overcomplicates swap code.

In try_to_unmap(), we already reject to unmap in case the page might be
pinned, because we must not lose PG_anon_exclusive on pinned pages ever.
Checking if there are other unexpected references reliably *before*
completely unmapping a page is unfortunately not really possible: THP
heavily overcomplicate the situation.  Once fully unmapped it's easier --
we, for example, make sure that there are no unexpected references *after*
unmapping a page before starting writeback on that page.

So, we currently might end up unmapping a page and clearing
PG_anon_exclusive if that page has additional references, for example, due
to a FOLL_GET.

do_swap_page() has to re-determine if a page is exclusive, which will
easily fail if there are other references on a page, most prominently GUP
references via FOLL_GET.  This can currently result in memory corruptions
when taking a FOLL_GET | FOLL_WRITE reference on a page even when fork()
is never involved: try_to_unmap() will succeed, and when refaulting the
page, it cannot be marked exclusive and will get replaced by a copy in the
page tables on the next write access, resulting in writes via the GUP
reference to the page being lost.

In an ideal world, everybody that uses GUP and wants to modify page
content, such as O_DIRECT, would properly use FOLL_PIN.  However, that
conversion will take a while.  It's easier to fix what used to work in the
past (FOLL_GET | FOLL_WRITE) remembering PG_anon_exclusive.  In addition,
by remembering PG_anon_exclusive we can further reduce unnecessary COW in
some cases, so it's the natural thing to do.

So let's transfer the PG_anon_exclusive information to the swap pte and
store it via an architecture-dependant pte bit; use that information when
restoring the swap pte in do_swap_page() and unuse_pte().  During fork(),
we simply have to clear the pte bit and are done.

Of course, there is one corner case to handle: swap backends that don't
support concurrent page modifications while the page is under writeback.
Special case these, and drop the exclusive marker.  Add a comment why that
is just fine (also, reuse_swap_page() would have done the same in the
past).

In the future, we'll hopefully have all architectures support
__HAVE_ARCH_PTE_SWP_EXCLUSIVE, such that we can get rid of the empty stubs
and the define completely.  Then, we can also convert
SWP_MIGRATION_READ_EXCLUSIVE.  For architectures it's fairly easy to
support: either simply use a yet unused pte bit that can be used for swap
entries, steal one from the arch type bits if they exceed 5, or steal one
from the offset bits.

Note: R/O FOLL_GET references were never really reliable, especially when
taking one on a shared page and then writing to the page (e.g., GUP after
fork()).  FOLL_GET, including R/W references, were never really reliable
once fork was involved (e.g., GUP before fork(), GUP during fork()).  KSM
steps back in case it stumbles over unexpected references and is,
therefore, fine.

[david@redhat.com: fix SWP_STABLE_WRITES test]
Link: https://lkml.kernel.org/r/ac725bcb-313a-4fff-250a-68ba9a8f85fb@redhat.comLink:
Link: https://lkml.kernel.org/r/20220329164329.208407-2-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Jann Horn <jannh@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Nadav Amit <namit@vmware.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/gup: sanity-check with CONFIG_DEBUG_VM that anonymous pages are exclusive when (un)pinning

Let's verify when (un)pinning anonymous pages that we always deal with
exclusive anonymous pages, which guarantees that we'll have a reliable
PIN, meaning that we cannot end up with the GUP pin being inconsistent
with he pages mapped into the page tables due to a COW triggered by a
write fault.

When pinning pages, after conditionally triggering GUP unsharing of
possibly shared anonymous pages, we should always only see exclusive
anonymous pages.  Note that anonymous pages that are mapped writable must
be marked exclusive, otherwise we'd have a BUG.

When pinning during ordinary GUP, simply add a check after our conditional
GUP-triggered unsharing checks.  As we know exactly how the page is
mapped, we know exactly in which page we have to check for
PageAnonExclusive().

When pinning via GUP-fast we have to be careful, because we can race with
fork(): verify only after we made sure via the seqcount that we didn't
race with concurrent fork() that we didn't end up pinning a possibly
shared anonymous page.

Similarly, when unpinning, verify that the pages are still marked as
exclusive: otherwise something turned the pages possibly shared, which can
result in random memory corruptions, which we really want to catch.

With only the pinned pages at hand and not the actual page table entries
we have to be a bit careful: hugetlb pages are always mapped via a single
logical page table entry referencing the head page and PG_anon_exclusive
of the head page applies.  Anon THP are a bit more complicated, because we
might have obtained the page reference either via a PMD or a PTE --
depending on the mapping type we either have to check PageAnonExclusive of
the head page (PMD-mapped THP) or the tail page (PTE-mapped THP) applies:
as we don't know and to make our life easier, check that either is set.

Take care to not verify in case we're unpinning during GUP-fast because we
detected concurrent fork(): we might stumble over an anonymous page that
is now shared.

Link: https://lkml.kernel.org/r/20220428083441.37290-18-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/gup: trigger FAULT_FLAG_UNSHARE when R/O-pinning a possibly shared anonymous page

Whenever GUP currently ends up taking a R/O pin on an anonymous page that
might be shared -- mapped R/O and !PageAnonExclusive() -- any write fault
on the page table entry will end up replacing the mapped anonymous page
due to COW, resulting in the GUP pin no longer being consistent with the
page actually mapped into the page table.

The possible ways to deal with this situation are:
 (1) Ignore and pin -- what we do right now.
 (2) Fail to pin -- which would be rather surprising to callers and
     could break user space.
 (3) Trigger unsharing and pin the now exclusive page -- reliable R/O
     pins.

Let's implement 3) because it provides the clearest semantics and allows
for checking in unpin_user_pages() and friends for possible BUGs: when
trying to unpin a page that's no longer exclusive, clearly something went
very wrong and might result in memory corruptions that might be hard to
debug.  So we better have a nice way to spot such issues.

This change implies that whenever user space *wrote* to a private mapping
(IOW, we have an anonymous page mapped), that GUP pins will always remain
consistent: reliable R/O GUP pins of anonymous pages.

As a side note, this commit fixes the COW security issue for hugetlb with
FOLL_PIN as documented in:
  https://lore.kernel.org/r/3ae33b08-d9ef-f846-56fb-645e3b9b4c66@redhat.com
The vmsplice reproducer still applies, because vmsplice uses FOLL_GET
instead of FOLL_PIN.

Note that follow_huge_pmd() doesn't apply because we cannot end up in
there with FOLL_PIN.

This commit is heavily based on prototype patches by Andrea.

Link: https://lkml.kernel.org/r/20220428083441.37290-17-david@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Co-developed-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: support GUP-triggered unsharing of anonymous pages

Whenever GUP currently ends up taking a R/O pin on an anonymous page that
might be shared -- mapped R/O and !PageAnonExclusive() -- any write fault
on the page table entry will end up replacing the mapped anonymous page
due to COW, resulting in the GUP pin no longer being consistent with the
page actually mapped into the page table.

The possible ways to deal with this situation are:
 (1) Ignore and pin -- what we do right now.
 (2) Fail to pin -- which would be rather surprising to callers and
     could break user space.
 (3) Trigger unsharing and pin the now exclusive page -- reliable R/O
     pins.

We want to implement 3) because it provides the clearest semantics and
allows for checking in unpin_user_pages() and friends for possible BUGs:
when trying to unpin a page that's no longer exclusive, clearly something
went very wrong and might result in memory corruptions that might be hard
to debug.  So we better have a nice way to spot such issues.

To implement 3), we need a way for GUP to trigger unsharing:
FAULT_FLAG_UNSHARE.  FAULT_FLAG_UNSHARE is only applicable to R/O mapped
anonymous pages and resembles COW logic during a write fault.  However, in
contrast to a write fault, GUP-triggered unsharing will, for example,
still maintain the write protection.

Let's implement FAULT_FLAG_UNSHARE by hooking into the existing write
fault handlers for all applicable anonymous page types: ordinary pages,
THP and hugetlb.

* If FAULT_FLAG_UNSHARE finds a R/O-mapped anonymous page that has been
  marked exclusive in the meantime by someone else, there is nothing to do.
* If FAULT_FLAG_UNSHARE finds a R/O-mapped anonymous page that's not
  marked exclusive, it will try detecting if the process is the exclusive
  owner. If exclusive, it can be set exclusive similar to reuse logic
  during write faults via page_move_anon_rmap() and there is nothing
  else to do; otherwise, we either have to copy and map a fresh,
  anonymous exclusive page R/O (ordinary pages, hugetlb), or split the
  THP.

This commit is heavily based on patches by Andrea.

Link: https://lkml.kernel.org/r/20220428083441.37290-16-david@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Co-developed-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/gup: disallow follow_page(FOLL_PIN)

We want to change the way we handle R/O pins on anonymous pages that might
be shared: if we detect a possibly shared anonymous page -- mapped R/O and
not !PageAnonExclusive() -- we want to trigger unsharing via a page fault,
resulting in an exclusive anonymous page that can be pinned reliably
without getting replaced via COW on the next write fault.

However, the required page fault will be problematic for follow_page(): in
contrast to ordinary GUP, follow_page() doesn't trigger faults internally.
So we would have to end up failing a R/O pin via follow_page(), although
there is something mapped R/O into the page table, which might be rather
surprising.

We don't seem to have follow_page(FOLL_PIN) users, and it's a purely
internal MM function.  Let's just make our life easier and the semantics
of follow_page() clearer by just disallowing FOLL_PIN for follow_page()
completely.

Link: https://lkml.kernel.org/r/20220428083441.37290-15-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/rmap: fail try_to_migrate() early when setting a PMD migration entry fails

Let's fail right away in case we cannot clear PG_anon_exclusive because
the anon THP may be pinned.  Right now, we continue trying to install
migration entries and the caller of try_to_migrate() will realize that the
page is still mapped and has to restore the migration entries.  Let's just
fail fast just like for PTE migration entries.

Link: https://lkml.kernel.org/r/20220428083441.37290-14-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: remember exclusively mapped anonymous pages with PG_anon_exclusive

Let's mark exclusively mapped anonymous pages with PG_anon_exclusive as
exclusive, and use that information to make GUP pins reliable and stay
consistent with the page mapped into the page table even if the page table
entry gets write-protected.

With that information at hand, we can extend our COW logic to always reuse
anonymous pages that are exclusive.  For anonymous pages that might be
shared, the existing logic applies.

As already documented, PG_anon_exclusive is usually only expressive in
combination with a page table entry.  Especially PTE vs.  PMD-mapped
anonymous pages require more thought, some examples: due to mremap() we
can easily have a single compound page PTE-mapped into multiple page
tables exclusively in a single process -- multiple page table locks apply.
Further, due to MADV_WIPEONFORK we might not necessarily write-protect
all PTEs, and only some subpages might be pinned.  Long story short: once
PTE-mapped, we have to track information about exclusivity per sub-page,
but until then, we can just track it for the compound page in the head
page and not having to update a whole bunch of subpages all of the time
for a simple PMD mapping of a THP.

For simplicity, this commit mostly talks about "anonymous pages", while
it's for THP actually "the part of an anonymous folio referenced via a
page table entry".

To not spill PG_anon_exclusive code all over the mm code-base, we let the
anon rmap code to handle all PG_anon_exclusive logic it can easily handle.

If a writable, present page table entry points at an anonymous (sub)page,
that (sub)page must be PG_anon_exclusive.  If GUP wants to take a reliably
pin (FOLL_PIN) on an anonymous page references via a present page table
entry, it must only pin if PG_anon_exclusive is set for the mapped
(sub)page.

This commit doesn't adjust GUP, so this is only implicitly handled for
FOLL_WRITE, follow-up commits will teach GUP to also respect it for
FOLL_PIN without FOLL_WRITE, to make all GUP pins of anonymous pages fully
reliable.

Whenever an anonymous page is to be shared (fork(), KSM), or when
temporarily unmapping an anonymous page (swap, migration), the relevant
PG_anon_exclusive bit has to be cleared to mark the anonymous page
possibly shared.  Clearing will fail if there are GUP pins on the page:

* For fork(), this means having to copy the page and not being able to
  share it.  fork() protects against concurrent GUP using the PT lock and
  the src_mm->write_protect_seq.

* For KSM, this means sharing will fail.  For swap this means, unmapping
  will fail, For migration this means, migration will fail early.  All
  three cases protect against concurrent GUP using the PT lock and a
  proper clear/invalidate+flush of the relevant page table entry.

This fixes memory corruptions reported for FOLL_PIN | FOLL_WRITE, when a
pinned page gets mapped R/O and the successive write fault ends up
replacing the page instead of reusing it.  It improves the situation for
O_DIRECT/vmsplice/...  that still use FOLL_GET instead of FOLL_PIN, if
fork() is *not* involved, however swapout and fork() are still
problematic.  Properly using FOLL_PIN instead of FOLL_GET for these GUP
users will fix the issue for them.

I. Details about basic handling

I.1. Fresh anonymous pages

page_add_new_anon_rmap() and hugepage_add_new_anon_rmap() will mark the
given page exclusive via __page_set_anon_rmap(exclusive=1).  As that is
the mechanism fresh anonymous pages come into life (besides migration code
where we copy the page->mapping), all fresh anonymous pages will start out
as exclusive.

I.2. COW reuse handling of anonymous pages

When a COW handler stumbles over a (sub)page that's marked exclusive, it
simply reuses it.  Otherwise, the handler tries harder under page lock to
detect if the (sub)page is exclusive and can be reused.  If exclusive,
page_move_anon_rmap() will mark the given (sub)page exclusive.

Note that hugetlb code does not yet check for PageAnonExclusive(), as it
still uses the old COW logic that is prone to the COW security issue
because hugetlb code cannot really tolerate unnecessary/wrong COW as huge
pages are a scarce resource.

I.3. Migration handling

try_to_migrate() has to try marking an exclusive anonymous page shared via
page_try_share_anon_rmap().  If it fails because there are GUP pins on the
page, unmap fails.  migrate_vma_collect_pmd() and
__split_huge_pmd_locked() are handled similarly.

Writable migration entries implicitly point at shared anonymous pages.
For readable migration entries that information is stored via a new
"readable-exclusive" migration entry, specific to anonymous pages.

When restoring a migration entry in remove_migration_pte(), information
about exlusivity is detected via the migration entry type, and
RMAP_EXCLUSIVE is set accordingly for
page_add_anon_rmap()/hugepage_add_anon_rmap() to restore that information.

I.4. Swapout handling

try_to_unmap() has to try marking the mapped page possibly shared via
page_try_share_anon_rmap().  If it fails because there are GUP pins on the
page, unmap fails.  For now, information about exclusivity is lost.  In
the future, we might want to remember that information in the swap entry
in some cases, however, it requires more thought, care, and a way to store
that information in swap entries.

I.5. Swapin handling

do_swap_page() will never stumble over exclusive anonymous pages in the
swap cache, as try_to_migrate() prohibits that.  do_swap_page() always has
to detect manually if an anonymous page is exclusive and has to set
RMAP_EXCLUSIVE for page_add_anon_rmap() accordingly.

I.6. THP handling

__split_huge_pmd_locked() has to move the information about exclusivity
from the PMD to the PTEs.

a) In case we have a readable-exclusive PMD migration entry, simply
   insert readable-exclusive PTE migration entries.

b) In case we have a present PMD entry and we don't want to freeze
   ("convert to migration entries"), simply forward PG_anon_exclusive to
   all sub-pages, no need to temporarily clear the bit.

c) In case we have a present PMD entry and want to freeze, handle it
   similar to try_to_migrate(): try marking the page shared first.  In
   case we fail, we ignore the "freeze" instruction and simply split
   ordinarily.  try_to_migrate() will properly fail because the THP is
   still mapped via PTEs.

When splitting a compound anonymous folio (THP), the information about
exclusivity is implicitly handled via the migration entries: no need to
replicate PG_anon_exclusive manually.

I.7.  fork() handling fork() handling is relatively easy, because
PG_anon_exclusive is only expressive for some page table entry types.

a) Present anonymous pages

page_try_dup_anon_rmap() will mark the given subpage shared -- which will
fail if the page is pinned.  If it failed, we have to copy (or PTE-map a
PMD to handle it on the PTE level).

Note that device exclusive entries are just a pointer at a PageAnon()
page.  fork() will first convert a device exclusive entry to a present
page table and handle it just like present anonymous pages.

b) Device private entry

Device private entries point at PageAnon() pages that cannot be mapped
directly and, therefore, cannot get pinned.

page_try_dup_anon_rmap() will mark the given subpage shared, which cannot
fail because they cannot get pinned.

c) HW poison entries

PG_anon_exclusive will remain untouched and is stale -- the page table
entry is just a placeholder after all.

d) Migration entries

Writable and readable-exclusive entries are converted to readable entries:
possibly shared.

I.8. mprotect() handling

mprotect() only has to properly handle the new readable-exclusive
migration entry:

When write-protecting a migration entry that points at an anonymous page,
remember the information about exclusivity via the "readable-exclusive"
migration entry type.

II. Migration and GUP-fast

Whenever replacing a present page table entry that maps an exclusive
anonymous page by a migration entry, we have to mark the page possibly
shared and synchronize against GUP-fast by a proper clear/invalidate+flush
to make the following scenario impossible:

1. try_to_migrate() places a migration entry after checking for GUP pins
   and marks the page possibly shared.

2. GUP-fast pins the page due to lack of synchronization

3. fork() converts the "writable/readable-exclusive" migration entry into a
   readable migration entry

4. Migration fails due to the GUP pin (failing to freeze the refcount)

5. Migration entries are restored. PG_anon_exclusive is lost

-> We have a pinned page that is not marked exclusive anymore.

Note that we move information about exclusivity from the page to the
migration entry as it otherwise highly overcomplicates fork() and
PTE-mapping a THP.

III. Swapout and GUP-fast

Whenever replacing a present page table entry that maps an exclusive
anonymous page by a swap entry, we have to mark the page possibly shared
and synchronize against GUP-fast by a proper clear/invalidate+flush to
make the following scenario impossible:

1. try_to_unmap() places a swap entry after checking for GUP pins and
   clears exclusivity information on the page.

2. GUP-fast pins the page due to lack of synchronization.

-> We have a pinned page that is not marked exclusive anymore.

If we'd ever store information about exclusivity in the swap entry,
similar to migration handling, the same considerations as in II would
apply.  This is future work.

Link: https://lkml.kernel.org/r/20220428083441.37290-13-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page-flags: reuse PG_mappedtodisk as PG_anon_exclusive for PageAnon() pages

The basic question we would like to have a reliable and efficient answer
to is: is this anonymous page exclusive to a single process or might it be
shared?  We need that information for ordinary/single pages, hugetlb
pages, and possibly each subpage of a THP.

Introduce a way to mark an anonymous page as exclusive, with the ultimate
goal of teaching our COW logic to not do "wrong COWs", whereby GUP pins
lose consistency with the pages mapped into the page table, resulting in
reported memory corruptions.

Most pageflags already have semantics for anonymous pages, however,
PG_mappedtodisk should never apply to pages in the swapcache, so let's
reuse that flag.

As PG_has_hwpoisoned also uses that flag on the second tail page of a
compound page, convert it to PG_error instead, which is marked as
PF_NO_TAIL, so never used for tail pages.

Use custom page flag modification functions such that we can do additional
sanity checks.  The semantics we'll put into some kernel doc in the future
are:

"
  PG_anon_exclusive is *usually* only expressive in combination with a
  page table entry. Depending on the page table entry type it might
  store the following information:

       Is what's mapped via this page table entry exclusive to the
       single process and can be mapped writable without further
       checks? If not, it might be shared and we might have to COW.

  For now, we only expect PTE-mapped THPs to make use of
  PG_anon_exclusive in subpages. For other anonymous compound
  folios (i.e., hugetlb), only the head page is logically mapped and
  holds this information.

  For example, an exclusive, PMD-mapped THP only has PG_anon_exclusive
  set on the head page. When replacing the PMD by a page table full
  of PTEs, PG_anon_exclusive, if set on the head page, will be set on
  all tail pages accordingly. Note that converting from a PTE-mapping
  to a PMD mapping using the same compound page is currently not
  possible and consequently doesn't require care.

  If GUP wants to take a reliable pin (FOLL_PIN) on an anonymous page,
  it should only pin if the relevant PG_anon_exclusive is set. In that
  case, the pin will be fully reliable and stay consistent with the pages
  mapped into the page table, as the bit cannot get cleared (e.g., by
  fork(), KSM) while the page is pinned. For anonymous pages that
  are mapped R/W, PG_anon_exclusive can be assumed to always be set
  because such pages cannot possibly be shared.

  The page table lock protecting the page table entry is the primary
  synchronization mechanism for PG_anon_exclusive; GUP-fast that does
  not take the PT lock needs special care when trying to clear the
  flag.

  Page table entry types and PG_anon_exclusive:
  * Present: PG_anon_exclusive applies.
  * Swap: the information is lost. PG_anon_exclusive was cleared.
  * Migration: the entry holds this information instead.
               PG_anon_exclusive was cleared.
  * Device private: PG_anon_exclusive applies.
  * Device exclusive: PG_anon_exclusive applies.
  * HW Poison: PG_anon_exclusive is stale and not changed.

  If the page may be pinned (FOLL_PIN), clearing PG_anon_exclusive is
  not allowed and the flag will stick around until the page is freed
  and folio->mapping is cleared.
"

We won't be clearing PG_anon_exclusive on destructive unmapping (i.e.,
zapping) of page table entries, page freeing code will handle that when
also invalidate page->mapping to not indicate PageAnon() anymore.  Letting
information about exclusivity stick around will be an important property
when adding sanity checks to unpinning code.

Note that we properly clear the flag in free_pages_prepare() via
PAGE_FLAGS_CHECK_AT_PREP for each individual subpage of a compound page,
so there is no need to manually clear the flag.

Link: https://lkml.kernel.org/r/20220428083441.37290-12-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/huge_memory: remove outdated VM_WARN_ON_ONCE_PAGE from unmap_page()

We can already theoretically fail to unmap (still having page_mapped()) in
case arch_unmap_one() fails, which can happen on sparc.  Failures to unmap
are handled gracefully, just as if there are other references on the
target page: freezing the refcount in split_huge_page_to_list() will fail
if still mapped and we'll simply remap.

In commit 504e070dc08f ("mm: thp: replace DEBUG_VM BUG with VM_WARN when
unmap fails for split") we already converted to VM_WARN_ON_ONCE_PAGE,
let's get rid of it completely now.

This is a preparation for making try_to_migrate() fail on anonymous pages
with GUP pins, which will make this VM_WARN_ON_ONCE_PAGE trigger more
frequently.

Link: https://lkml.kernel.org/r/20220428083441.37290-11-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reported-by: Yang Shi <shy828301@gmail.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/rmap: use page_move_anon_rmap() when reusing a mapped PageAnon() page exclusively

We want to mark anonymous pages exclusive, and when using
page_move_anon_rmap() we know that we are the exclusive user, as properly
documented.  This is a preparation for marking anonymous pages exclusive
in page_move_anon_rmap().

In both instances, we're holding page lock and are sure that we're the
exclusive owner (page_count() == 1).  hugetlb already properly uses
page_move_anon_rmap() in the write fault handler.

Note that in case of a PTE-mapped THP, we'll only end up calling this
function if the whole THP is only referenced by the single PTE mapping a
single subpage (page_count() == 1); consequently, it's fine to modify the
compound page mapping inside page_move_anon_rmap().

Link: https://lkml.kernel.org/r/20220428083441.37290-10-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/rmap: drop "compound" parameter from page_add_new_anon_rmap()

New anonymous pages are always mapped natively: only THP/khugepaged code
maps a new compound anonymous page and passes "true".  Otherwise, we're
just dealing with simple, non-compound pages.

Let's give the interface clearer semantics and document these.  Remove the
PageTransCompound() sanity check from page_add_new_anon_rmap().

Link: https://lkml.kernel.org/r/20220428083441.37290-9-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/rmap: pass rmap flags to hugepage_add_anon_rmap()

Let's prepare for passing RMAP_EXCLUSIVE, similarly as we do for
page_add_anon_rmap() now.  RMAP_COMPOUND is implicit for hugetlb pages and
ignored.

Link: https://lkml.kernel.org/r/20220428083441.37290-8-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/rmap: remove do_page_add_anon_rmap()

... and instead convert page_add_anon_rmap() to accept flags.

Passing flags instead of bools is usually nicer either way, and we want to
more often also pass RMAP_EXCLUSIVE in follow up patches when detecting
that an anonymous page is exclusive: for example, when restoring an
anonymous page from a writable migration entry.

This is a preparation for marking an anonymous page inside
page_add_anon_rmap() as exclusive when RMAP_EXCLUSIVE is passed.

Link: https://lkml.kernel.org/r/20220428083441.37290-7-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/rmap: convert RMAP flags to a proper distinct rmap_t type

We want to pass the flags to more than one anon rmap function, getting rid
of special "do_page_add_anon_rmap()".  So let's pass around a distinct
__bitwise type and refine documentation.

Link: https://lkml.kernel.org/r/20220428083441.37290-6-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/rmap: split page_dup_rmap() into page_dup_file_rmap() and page_try_dup_anon_rmap()

...  and move the special check for pinned pages into
page_try_dup_anon_rmap() to prepare for tracking exclusive anonymous pages
via a new pageflag, clearing it only after making sure that there are no
GUP pins on the anonymous page.

We really only care about pins on anonymous pages, because they are prone
to getting replaced in the COW handler once mapped R/O.  For !anon pages
in cow-mappings (!VM_SHARED && VM_MAYWRITE) we shouldn't really care about
that, at least not that I could come up with an example.

Let's drop the is_cow_mapping() check from page_needs_cow_for_dma(), as we
know we're dealing with anonymous pages.  Also, drop the handling of
pinned pages from copy_huge_pud() and add a comment if ever supporting
anonymous pages on the PUD level.

This is a preparation for tracking exclusivity of anonymous pages in the
rmap code, and disallowing marking a page shared (-> failing to duplicate)
if there are GUP pins on a page.

Link: https://lkml.kernel.org/r/20220428083441.37290-5-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memory: slightly simplify copy_present_pte()

Let's move the pinning check into the caller, to simplify return code
logic and prepare for further changes: relocating the
page_needs_cow_for_dma() into rmap handling code.

While at it, remove the unused pte parameter and simplify the comments a
bit.

No functional change intended.

Link: https://lkml.kernel.org/r/20220428083441.37290-4-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/hugetlb: take src_mm->write_protect_seq in copy_hugetlb_page_range()

Let's do it just like copy_page_range(), taking the seqlock and making
sure the mmap_lock is held in write mode.

This allows for add a VM_BUG_ON to page_needs_cow_for_dma() and properly
synchronizes concurrent fork() with GUP-fast of hugetlb pages, which will
be relevant for further changes.

Link: https://lkml.kernel.org/r/20220428083441.37290-3-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/rmap: fix missing swap_free() in try_to_unmap() after arch_unmap_one() failed

Patch series "mm: COW fixes part 2: reliable GUP pins of anonymous pages", v4.

This series is the result of the discussion on the previous approach [2].
More information on the general COW issues can be found there.  It is
based on latest linus/master (post v5.17, with relevant core-MM changes
for v5.18-rc1).

This series fixes memory corruptions when a GUP pin (FOLL_PIN) was taken
on an anonymous page and COW logic fails to detect exclusivity of the page
to then replacing the anonymous page by a copy in the page table: The GUP
pin lost synchronicity with the pages mapped into the page tables.

This issue, including other related COW issues, has been summarized in [3]
under 3):
"
  3. Intra Process Memory Corruptions due to Wrong COW (FOLL_PIN)

  page_maybe_dma_pinned() is used to check if a page may be pinned for
  DMA (using FOLL_PIN instead of FOLL_GET).  While false positives are
  tolerable, false negatives are problematic: pages that are pinned for
  DMA must not be added to the swapcache.  If it happens, the (now pinned)
  page could be faulted back from the swapcache into page tables
  read-only.  Future write-access would detect the pinning and COW the
  page, losing synchronicity.  For the interested reader, this is nicely
  documented in feb889fb40fa ("mm: don't put pinned pages into the swap
  cache").

  Peter reports [8] that page_maybe_dma_pinned() as used is racy in some
  cases and can result in a violation of the documented semantics: giving
  false negatives because of the race.

  There are cases where we call it without properly taking a per-process
  sequence lock, turning the usage of page_maybe_dma_pinned() racy.  While
  one case (clear_refs SOFTDIRTY tracking, see below) seems to be easy to
  handle, there is especially one rmap case (shrink_page_list) that's hard
  to fix: in the rmap world, we're not limited to a single process.

  The shrink_page_list() issue is really subtle.  If we race with
  someone pinning a page, we can trigger the same issue as in the FOLL_GET
  case.  See the detail section at the end of this mail on a discussion
  how bad this can bite us with VFIO or other FOLL_PIN user.

  It's harder to reproduce, but I managed to modify the O_DIRECT
  reproducer to use io_uring fixed buffers [15] instead, which ends up
  using FOLL_PIN | FOLL_WRITE | FOLL_LONGTERM to pin buffer pages and can
  similarly trigger a loss of synchronicity and consequently a memory
  corruption.

  Again, the root issue is that a write-fault on a page that has
  additional references results in a COW and thereby a loss of
  synchronicity and consequently a memory corruption if two parties
  believe they are referencing the same page.
"

This series makes GUP pins (R/O and R/W) on anonymous pages fully
reliable, especially also taking care of concurrent pinning via GUP-fast,
for example, also fully fixing an issue reported regarding NUMA balancing
[4] recently.  While doing that, it further reduces "unnecessary COWs",
especially when we don't fork()/KSM and don't swapout, and fixes the COW
security for hugetlb for FOLL_PIN.

In summary, we track via a pageflag (PG_anon_exclusive) whether a mapped
anonymous page is exclusive.  Exclusive anonymous pages that are mapped
R/O can directly be mapped R/W by the COW logic in the write fault
handler.  Exclusive anonymous pages that want to be shared (fork(), KSM)
first have to be marked shared -- which will fail if there are GUP pins on
the page.  GUP is only allowed to take a pin on anonymous pages that are
exclusive.  The PT lock is the primary mechanism to synchronize
modifications of PG_anon_exclusive.  We synchronize against GUP-fast
either via the src_mm->write_protect_seq (during fork()) or via
clear/invalidate+flush of the relevant page table entry.

Special care has to be taken about swap, migration, and THPs (whereby a
PMD-mapping can be converted to a PTE mapping and we have to track
information for subpages).  Besides these, we let the rmap code handle
most magic.  For reliable R/O pins of anonymous pages, we need
FAULT_FLAG_UNSHARE logic as part of our previous approach [2], however,
it's now 100% mapcount free and I further simplified it a bit.

  #1 is a fix
  #3-#10 are mostly rmap preparations for PG_anon_exclusive handling
  #11 introduces PG_anon_exclusive
  #12 uses PG_anon_exclusive and make R/W pins of anonymous pages
   reliable
  #13 is a preparation for reliable R/O pins
  #14 and #15 is reused/modified GUP-triggered unsharing for R/O GUP pins
   make R/O pins of anonymous pages reliable
  #16 adds sanity check when (un)pinning anonymous pages

[1] https://lkml.kernel.org/r/20220131162940.210846-1-david@redhat.com
[2] https://lkml.kernel.org/r/20211217113049.23850-1-david@redhat.com
[3] https://lore.kernel.org/r/3ae33b08-d9ef-f846-56fb-645e3b9b4c66@redhat.com
[4] https://bugzilla.kernel.org/show_bug.cgi?id=215616

This patch (of 17):

In case arch_unmap_one() fails, we already did a swap_duplicate().  let's
undo that properly via swap_free().

Link: https://lkml.kernel.org/r/20220428083441.37290-1-david@redhat.com
Link: https://lkml.kernel.org/r/20220428083441.37290-2-david@redhat.com
Fixes: ca827d55ebaa ("mm, swap: Add infrastructure for saving page metadata on swap")
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Khalid Aziz <khalid.aziz@oracle.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Jann Horn <jannh@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Nadav Amit <namit@vmware.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/damon/reclaim: fix the timer always stays active

The timer stays active even if the reclaim mechanism is never enabled.  It
is unnecessary overhead can be completely avoided by using
module_param_cb() for enabled flag.

Link: https://lkml.kernel.org/r/20220421125910.1052459-1-tuhailong@gmail.com
Signed-off-by: Hailong Tu <tuhailong@gmail.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/damon: remove unnecessary type castings

Remove unnecessary void* type castings.

Link: https://lkml.kernel.org/r/20220421153056.8474-1-yuzhe@nfschina.com
Signed-off-by: Yu Zhe <yuzhe@nfschina.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: liqiong <liqiong@nfschina.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/damon/core-test: add a kunit test case for ops registration

This commit adds a simple kunit test case for DAMON operations
registration feature.

Link: https://lkml.kernel.org/r/20220419122225.290518-1-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

damon: vaddr-test: tweak code to make the logic clearer

Move these two lines into the damon_for_each_region loop, it is always for
testing the last region.  And also avoid to use a list iterator 'r'
outside the loop which is considered harmful[1].

[1]:  https://lkml.org/lkml/2022/2/17/1032

Link: https://lkml.kernel.org/r/20220328115252.31675-1-xiam0nd.tong@gmail.com
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

selftests: cgroup: add a selftest for memory.reclaim

Add a new test for memory.reclaim that verifies that the interface
correctly reclaims memory as intended, from both anon and file pages.

Link: https://lkml.kernel.org/r/20220425190040.2475377-5-yosryahmed@google.com
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Chen Wandun <chenwandun@huawei.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Michal Koutn" <mkoutny@suse.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Vaibhav Jain <vaibhav@linux.ibm.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Zefan Li <lizefan.x@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

selftests: cgroup: fix alloc_anon_noexit() instantly freeing memory

Currently, alloc_anon_noexit() calls alloc_anon() which instantly frees
the allocated memory. alloc_anon_noexit() is usually used with
cg_run_nowait() to run a process in the background that allocates
memory. It makes sense for the background process to keep the memory
allocated and not instantly free it (otherwise there is no point of
running it in the background).

Link: https://lkml.kernel.org/r/20220425190040.2475377-4-yosryahmed@google.com
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Chen Wandun <chenwandun@huawei.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Michal Koutn" <mkoutny@suse.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Vaibhav Jain <vaibhav@linux.ibm.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Zefan Li <lizefan.x@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

selftests: cgroup: return -errno from cg_read()/cg_write() on failure

Currently, cg_read()/cg_write() returns 0 on success and -1 on failure.
Modify them to return the -errno on failure.

Link: https://lkml.kernel.org/r/20220425190040.2475377-3-yosryahmed@google.com
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Chen Wandun <chenwandun@huawei.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Michal Koutn" <mkoutny@suse.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Vaibhav Jain <vaibhav@linux.ibm.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Zefan Li <lizefan.x@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

memcg: introduce per-memcg reclaim interface

This patch series adds a memory.reclaim proactive reclaim interface.
The rationale behind the interface and how it works are in the first
patch.

This patch (of 4):

Introduce a memcg interface to trigger memory reclaim on a memory cgroup.

Use case: Proactive Reclaim
---------------------------

A userspace proactive reclaimer can continuously probe the memcg to
reclaim a small amount of memory.  This gives more accurate and up-to-date
workingset estimation as the LRUs are continuously sorted and can
potentially provide more deterministic memory overcommit behavior.  The
memory overcommit controller can provide more proactive response to the
changing behavior of the running applications instead of being reactive.

A userspace reclaimer's purpose in this case is not a complete replacement
for kswapd or direct reclaim, it is to proactively identify memory savings
opportunities and reclaim some amount of cold pages set by the policy to
free up the memory for more demanding jobs or scheduling new jobs.

A user space proactive reclaimer is used in Google data centers.
Additionally, Meta's TMO paper recently referenced a very similar
interface used for user space proactive reclaim:
https://dl.acm.org/doi/pdf/10.1145/3503222.3507731

Benefits of a user space reclaimer:
-----------------------------------

1) More flexible on who should be charged for the cpu of the memory
   reclaim.  For proactive reclaim, it makes more sense to be centralized.

2) More flexible on dedicating the resources (like cpu).  The memory
   overcommit controller can balance the cost between the cpu usage and
   the memory reclaimed.

3) Provides a way to the applications to keep their LRUs sorted, so,
   under memory pressure better reclaim candidates are selected.  This
   also gives more accurate and uptodate notion of working set for an
   application.

Why memory.high is not enough?
------------------------------

- memory.high can be used to trigger reclaim in a memcg and can
  potentially be used for proactive reclaim.  However there is a big
  downside in using memory.high.  It can potentially introduce high
  reclaim stalls in the target application as the allocations from the
  processes or the threads of the application can hit the temporary
  memory.high limit.

- Userspace proactive reclaimers usually use feedback loops to decide
  how much memory to proactively reclaim from a workload.  The metrics
  used for this are usually either refaults or PSI, and these metrics will
  become messy if the application gets throttled by hitting the high
  limit.

- memory.high is a stateful interface, if the userspace proactive
  reclaimer crashes for any reason while triggering reclaim it can leave
  the application in a bad state.

- If a workload is rapidly expanding, setting memory.high to proactively
  reclaim memory can result in actually reclaiming more memory than
  intended.

The benefits of such interface and shortcomings of existing interface were
further discussed in this RFC thread:
https://lore.kernel.org/linux-mm/5df21376-7dd1-bf81-8414-32a73cea45dd@google.com/

Interface:
----------

Introducing a very simple memcg interface 'echo 10M > memory.reclaim' to
trigger reclaim in the target memory cgroup.

The interface is introduced as a nested-keyed file to allow for future
optional arguments to be easily added to configure the behavior of
reclaim.

Possible Extensions:
--------------------

- This interface can be extended with an additional parameter or flags
  to allow specifying one or more types of memory to reclaim from (e.g.
  file, anon, ..).

- The interface can also be extended with a node mask to reclaim from
  specific nodes. This has use cases for reclaim-based demotion in memory
  tiering systens.

- A similar per-node interface can also be added to support proactive
  reclaim and reclaim-based demotion in systems without memcg.

- Add a timeout parameter to make it easier for user space to call the
  interface without worrying about being blocked for an undefined amount
  of time.

For now, let's keep things simple by adding the basic functionality.

[yosryahmed@google.com: worked on versions v2 onwards, refreshed to
current master, updated commit message based on recent
discussions and use cases]
Link: https://lkml.kernel.org/r/20220425190040.2475377-1-yosryahmed@google.com
Link: https://lkml.kernel.org/r/20220425190040.2475377-2-yosryahmed@google.com
Signed-off-by: Shakeel Butt <shakeelb@google.com>
Co-developed-by: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Wei Xu <weixugc@google.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Zefan Li <lizefan.x@bytedance.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Chen Wandun <chenwandun@huawei.com>
Cc: Vaibhav Jain <vaibhav@linux.ibm.com>
Cc: "Michal Koutn" <mkoutny@suse.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

zram: add a huge_idle writeback mode

Today it's only possible to write back as a page, idle, or huge.  A user
might want to writeback pages which are huge and idle first as these idle
pages do not require decompression and make a good first pass for
writeback.

Idle writeback specifically has the advantage that a refault is unlikely
given that the page has been swapped for some amount of time without being
refaulted.

Huge writeback has the advantage that you're guaranteed to get the maximum
benefit from a single page writeback, that is, you're reclaiming one full
page of memory.  Pages which are compressed in zram being written back
result in some benefit which is always less than a page size because of
the fact that it was compressed.

The primary use of this is for minimizing refaults in situations where the
device has to be sensitive to storage endurance.  On ChromeOS we have
devices with slow eMMC and repeated writes and refaults can negatively
affect performance and endurance.

Link: https://lkml.kernel.org/r/20220322215821.1196994-1-bgeffon@google.com
Signed-off-by: Brian Geffon <bgeffon@google.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_alloc: simplify update of pgdat in wake_all_kswapds

There is no need to update last_pgdat for each zone, only update
last_pgdat when iterating the first zone of a node.

Link: https://lkml.kernel.org/r/20220322115635.2708989-1-chenwandun@huawei.com
Signed-off-by: Chen Wandun <chenwandun@huawei.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

kasan: mark KASAN_VMALLOC flags as kasan_vmalloc_flags_t

Fix sparse warning:

mm/kasan/shadow.c:496:15: warning: restricted kasan_vmalloc_flags_t degrades to integer

Link: https://lkml.kernel.org/r/52d8fccdd3a48d4bdfd0ff522553bac2a13f1579.1649351254.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reported-by: kernel test robot <lkp@intel.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

kasan: fix sleeping function called from invalid context on RT kernel

BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46
in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 1, name: swapper/0
preempt_count: 1, expected: 0
...........
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.17.1-rt16-yocto-preempt-rt #22
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009),
BIOS rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x60/0x8c
dump_stack+0x10/0x12
 __might_resched.cold+0x13b/0x173
rt_spin_lock+0x5b/0xf0
 ___cache_free+0xa5/0x180
qlist_free_all+0x7a/0x160
per_cpu_remove_cache+0x5f/0x70
smp_call_function_many_cond+0x4c4/0x4f0
on_each_cpu_cond_mask+0x49/0xc0
kasan_quarantine_remove_cache+0x54/0xf0
kasan_cache_shrink+0x9/0x10
kmem_cache_shrink+0x13/0x20
acpi_os_purge_cache+0xe/0x20
acpi_purge_cached_objects+0x21/0x6d
acpi_initialize_objects+0x15/0x3b
acpi_init+0x130/0x5ba
do_one_initcall+0xe5/0x5b0
kernel_init_freeable+0x34f/0x3ad
kernel_init+0x1e/0x140
ret_from_fork+0x22/0x30

When the kmem_cache_shrink() was called, the IPI was triggered, the
___cache_free() is called in IPI interrupt context, the local-lock or
spin-lock will be acquired.  On PREEMPT_RT kernel, these locks are
replaced with sleepbale rt-spinlock, so the above problem is triggered.
Fix it by moving the qlist_free_allfrom() from IPI interrupt context to
task context when PREEMPT_RT is enabled.

[akpm@linux-foundation.org: reduce ifdeffery]
Link: https://lkml.kernel.org/r/20220401134649.2222485-1-qiang1.zhang@intel.com
Signed-off-by: Zqiang <qiang1.zhang@intel.com>
Acked-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: hugetlb: add missing cache flushing in hugetlb_unshare_all_pmds()

Missed calling flush_cache_range() before removing the sharing PMD
entrires, otherwise data consistence issue may be occurred on some
architectures whose caches are strict and require a virtual>physical
translation to exist for a virtual address.  Thus add it.

Now no architectures enabling PMD sharing will be affected, since they do
not have a VIVT cache.  That means this issue can not be happened in
practice so far.

Link: https://lkml.kernel.org/r/47441086affcabb6ecbe403173e9283b0d904b38.1650956489.git.baolin.wang@linux.alibaba.com
Link: https://lkml.kernel.org/r/419b0e777c9e6d1454dcd906e0f5b752a736d335.1650781755.git.baolin.wang@linux.alibaba.com
Fixes: 6dfeaff93be1 ("hugetlb/userfaultfd: unshare all pmds for hugetlbfs when register wp")
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/khugepaged: use vma_is_anonymous

Clean up the vma->vm_ops usage.  Use vma_is_anonymous instead of
vma->vm_ops to make it more understandable.

Link: https://lkml.kernel.org/r/20220424071642.3234971-1-xu.xin16@zte.com.cn
Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: use for_each_online_node and node_online instead of open coding

Use more generic functions to deal with issues related to online nodes.
The changes will make the code simplified.

Link: https://lkml.kernel.org/r/20220429030218.644635-1-liupeng256@huawei.com
Signed-off-by: Peng Liu <liupeng256@huawei.com>
Suggested-by: Davidlohr Bueso <dave@stgolabs.net>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

hugetlb: fix return value of __setup handlers

When __setup() return '0', using invalid option values causes the entire
kernel boot option string to be reported as Unknown.  Hugetlb calls
__setup() and will return '0' when set invalid parameter string.

The following phenomenon is observed:
 cmdline:
  hugepagesz=1Y hugepages=1
 dmesg:
  HugeTLB: unsupported hugepagesz=1Y
  HugeTLB: hugepages=1 does not follow a valid hugepagesz, ignoring
  Unknown kernel command line parameters "hugepagesz=1Y hugepages=1"

Since hugetlb will print warning/error information before return for
invalid parameter string, just use return '1' to avoid print again.

Link: https://lkml.kernel.org/r/20220413032915.251254-4-liupeng256@huawei.com
Signed-off-by: Peng Liu <liupeng256@huawei.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Liu Yuntao <liuyuntao10@huawei.com>
Cc: Zhenguo Yao <yaozhenguo1@gmail.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

hugetlb: fix hugepages_setup when deal with pernode

Hugepages can be specified to pernode since "hugetlbfs: extend the
definition of hugepages parameter to support node allocation", but the
following problem is observed.

Confusing behavior is observed when both 1G and 2M hugepage is set
after "numa=off".
 cmdline hugepage settings:
  hugepagesz=1G hugepages=0:3,1:3
  hugepagesz=2M hugepages=0:1024,1:1024
 results:
  HugeTLB registered 1.00 GiB page size, pre-allocated 0 pages
  HugeTLB registered 2.00 MiB page size, pre-allocated 1024 pages

Furthermore, confusing behavior can be also observed when an invalid node
behind a valid node.  To fix this, never allocate any typical hugepage
when an invalid parameter is received.

Link: https://lkml.kernel.org/r/20220413032915.251254-3-liupeng256@huawei.com
Fixes: b5389086ad7b ("hugetlbfs: extend the definition of hugepages parameter to support node allocation")
Signed-off-by: Peng Liu <liupeng256@huawei.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Liu Yuntao <liuyuntao10@huawei.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Zhenguo Yao <yaozhenguo1@gmail.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

hugetlb: fix wrong use of nr_online_nodes

Patch series "hugetlb: Fix some incorrect behavior", v3.

This series fix three bugs of hugetlb:
1) Invalid use of nr_online_nodes;
2) Inconsistency between 1G hugepage and 2M hugepage;
3) Useless information in dmesg.

This patch (of 4):

Certain systems are designed to have sparse/discontiguous nodes.  In this
case, nr_online_nodes can not be used to walk through numa node.  Also, a
valid node may be greater than nr_online_nodes.

However, in hugetlb, it is assumed that nodes are contiguous.

For sparse/discontiguous nodes, the current code may treat a valid node
as invalid, and will fail to allocate all hugepages on a valid node that
"nid >= nr_online_nodes".

As David suggested:

if (tmp >= nr_online_nodes)
goto invalid;

Just imagine node 0 and node 2 are online, and node 1 is offline.
Assuming that "node < 2" is valid is wrong.

Recheck all the places that use nr_online_nodes, and repair them one by
one.

[liupeng256@huawei.com: v4]
Link: https://lkml.kernel.org/r/20220416103526.3287348-1-liupeng256@huawei.com
Link: https://lkml.kernel.org/r/20220413032915.251254-1-liupeng256@huawei.com
Link: https://lkml.kernel.org/r/20220413032915.251254-2-liupeng256@huawei.com
Fixes: 4178158ef8ca ("hugetlbfs: fix issue of preallocation of gigantic pages can't work")
Fixes: b5389086ad7b ("hugetlbfs: extend the definition of hugepages parameter to support node allocation")
Fixes: e79ce9832316 ("hugetlbfs: fix a truncation issue in hugepages parameter")
Fixes: f9317f77a6e0 ("hugetlb: clean up potential spectre issue warnings")
Signed-off-by: Peng Liu <liupeng256@huawei.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Zhenguo Yao <yaozhenguo1@gmail.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Liu Yuntao <liuyuntao10@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/base/memory: fix an unlikely reference counting issue in __add_memory_block()

__add_memory_block() calls both put_device() and device_unregister() when
storing the memory block into the xarray.  This is incorrect because
xarray doesn't take an additional reference and device_unregister()
already calls put_device().

Triggering the issue looks really unlikely and its only effect should be
to log a spurious warning about a ref counted issue.

Link: https://lkml.kernel.org/r/d44c63d78affe844f020dc02ad6af29abc448fc4.1650611702.git.christophe.jaillet@wanadoo.fr
Fixes: 4fb6eabf1037 ("drivers/base/memory.c: cache memory blocks in xarray to accelerate lookup")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Scott Cheloha <cheloha@linux.vnet.ibm.com>
Cc: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: compaction: make sure highest is above the min_pfn

It's not guaranteed that highest will be above the min_pfn.  If highest is
below the min_pfn, migrate_pfn and free_pfn can meet prematurely and lead
to some useless work.  Make sure highest is above min_pfn to avoid making
a futile effort.

Link: https://lkml.kernel.org/r/20220418141253.24298-13-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Charan Teja Kalla <charante@codeaurora.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Pintu Kumar <pintu@codeaurora.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: compaction: simplify the code in __compact_finished

Since commit efe771c7603b ("mm, compaction: always finish scanning of a
full pageblock"), compaction will always finish scanning a pageblock.  And
migrate_pfn is assured to align with pageblock_nr_pages when we reach
here.  So we will always return COMPACT_SUCCESS if a suitable fallback is
found due to the below IS_ALIGNED check of migrate_pfn.  Simplify the code
to make this clear and improve the readability.  No functional change
intended.

Link: https://lkml.kernel.org/r/20220418141253.24298-12-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Charan Teja Kalla <charante@codeaurora.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Pintu Kumar <pintu@codeaurora.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: compaction: make compaction_zonelist_suitable return false when COMPACT_SUCCESS

When compact_result indicates that the allocation should now succeed, i.e.
compact_result = COMPACT_SUCCESS, compaction_zonelist_suitable should
return false because there is no need to do compaction now.

Link: https://lkml.kernel.org/r/20220418141253.24298-11-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Charan Teja Kalla <charante@codeaurora.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Pintu Kumar <pintu@codeaurora.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: compaction: avoid possible NULL pointer dereference in kcompactd_cpu_online

It's possible that kcompactd_run could fail to run kcompactd for a hot
added node and leave pgdat->kcompactd as NULL.  So pgdat->kcompactd should
be checked here to avoid possible NULL pointer dereference.

Link: https://lkml.kernel.org/r/20220418141253.24298-10-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Charan Teja Kalla <charante@codeaurora.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Pintu Kumar <pintu@codeaurora.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: compaction: clean up comment about async compaction in isolate_migratepages

Since commit 282722b0d258 ("mm, compaction: restrict async compaction to
pageblocks of same migratetype"), async direct compaction is restricted to
scan the pageblocks of same migratetype.  Correct the comment accordingly.

Link: https://lkml.kernel.org/r/20220418141253.24298-9-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Charan Teja Kalla <charante@codeaurora.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Pintu Kumar <pintu@codeaurora.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: compaction: use helper compound_nr in isolate_migratepages_block

Use helper compound_nr to make use of compound_nr when CONFIG_64BIT and
simplify the code a bit.

Link: https://lkml.kernel.org/r/20220418141253.24298-8-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Charan Teja Kalla <charante@codeaurora.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Pintu Kumar <pintu@codeaurora.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: compaction: use COMPACT_CLUSTER_MAX in compaction.c

Always use COMPACT_CLUSTER_MAX here as we're doing the compaction.  Minor
improvements in readability.

Link: https://lkml.kernel.org/r/20220418141253.24298-7-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Charan Teja Kalla <charante@codeaurora.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Pintu Kumar <pintu@codeaurora.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: compaction: clean up comment about suitable migration target recheck

checked_pageblock is already removed and suitable_migration_target is not
rechecked under the zone lock since commit f8224aa5a0a4 ("mm, compaction:
do not recheck suitable_migration_target under lock").  Correct the
comment accordingly.

Link: https://lkml.kernel.org/r/20220418141253.24298-6-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Charan Teja Kalla <charante@codeaurora.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Pintu Kumar <pintu@codeaurora.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: compaction: clean up comment for sched contention

Since commit cf66f0700c8f ("mm, compaction: do not consider a need to
reschedule as contention"), async compaction won't abort when scheduling
is needed.  Correct the relevant comment accordingly.

Link: https://lkml.kernel.org/r/20220418141253.24298-5-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Charan Teja Kalla <charante@codeaurora.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Pintu Kumar <pintu@codeaurora.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: compaction: remove unneeded assignment to isolate_start_pfn

isolate_start_pfn is unused when cc->nr_freepages !  = 0.  Otherwise
cc->free_pfn will overwrite it unconditionally.  So we should remove this
unneeded and somewhat misleading assignment.

Link: https://lkml.kernel.org/r/20220418141253.24298-4-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Charan Teja Kalla <charante@codeaurora.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Pintu Kumar <pintu@codeaurora.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: compaction: remove unneeded pfn update

pfn is unused in this do while loop. Remove the unneeded pfn update.

Link: https://lkml.kernel.org/r/20220418141253.24298-3-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Charan Teja Kalla <charante@codeaurora.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Pintu Kumar <pintu@codeaurora.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: compaction: remove unneeded return value of kcompactd_run

Patch series "A few cleanup and fixup patches for compaction".

This series contains a few patches to clean up some obsolete comment,
remove unneeded return value and so on.  Also we fix the possible NULL
pointer dereference.  More details can be found in the respective
changelogs.

This patch (of 12):

The return value of kcompactd_run() is unused now.  Clean it up.

Link: https://lkml.kernel.org/r/20220418141253.24298-1-linmiaohe@huawei.com
Link: https://lkml.kernel.org/r/20220418141253.24298-2-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc; Mel Gorman <mgorman@techsingularity.net>
Cc: David Hildenbrand <david@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Pintu Kumar <pintu@codeaurora.org>
Cc: Charan Teja Kalla <charante@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/vmstat: add events for ksm cow

Users may use ksm by calling madvise(, , MADV_MERGEABLE) when they want to
save memory, it's a tradeoff by suffering delay on ksm cow.  Users can get
to know how much memory ksm saved by reading
/sys/kernel/mm/ksm/pages_sharing, but they don't know what's the costs of
ksm cow, and this is important of some delay sensitive tasks.

So add ksm cow events to help users evaluate whether or how to use ksm.
Also update Documentation/admin-guide/mm/ksm.rst with new added events.

Link: https://lkml.kernel.org/r/20220331035616.2390805-1-yang.yang29@zte.com.cn
Signed-off-by: Yang Yang <yang.yang29@zte.com.cn>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: xu xin <xu.xin16@zte.com.cn>
Reviewed-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Saravanan D <saravanand@fb.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

ksm: count ksm merging pages for each process

Some applications or containers want to use KSM by calling madvise() to
advise areas of address space to be MERGEABLE.  But they may not know
which applications are more likely to cause real merges in the
deployment.  If this patch is applied, it helps them know their
corresponding number of merged pages, and then optimize their app code.

As current KSM only counts the number of KSM merging pages(e.g.
ksm_pages_sharing and ksm_pages_shared) of the whole system, we cannot see
the more fine-grained KSM merging, for the upper application optimization,
the merging area cannot be set easily according to the KSM page merging
probability of each process.  Therefore, it is necessary to add extra
statistical means so that the upper level users can know the detailed KSM
merging information of each process.

We add a new proc file named as ksm_merging_pages under /proc/<pid>/ to
indicate the involved ksm merging pages of this process.

[akpm@linux-foundation.org: fix comment typo, remove BUG_ON()s]
Link: https://lkml.kernel.org/r/20220325082318.2352853-1-xu.xin16@zte.com.cn
Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Yang Yang <yang.yang29@zte.com.cn>
Reviewed-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Reported-by: Zeal Robot <zealci@zte.com.cn>
Cc: Kees Cook <keescook@chromium.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Ohhoon Kwon <ohoono.kwon@samsung.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Stephen Brennan <stephen.s.brennan@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Feng Tang <feng.tang@intel.com>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Cc: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Cc: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/swapops.h: remove stub for non_swap_entry()

The stub for non_swap_entry() may not help much, because MAX_SWAPFILES has
already contained all the information to decide whether a swap entry is
real swap entry or pesudo ones (migrations, ...).

There can be some performance influences on non_swap_entry() with below
conditions all met:

  !CONFIG_MIGRATION && !CONFIG_MEMORY_FAILURE && !CONFIG_DEVICE_PRIVATE

But that's definitely not the major config most machines will use, at the
meantime it's already in a slow path of swap entry (being parsed from a
swap pte), so IMHO it shouldn't be a major issue.  Also according to the
analysis from Alistair, somehow the stub didn't do the job right [1].

To make the code cleaner, let's drop the stub.

[1] https://lore.kernel.org/lkml/8735ihbw6g.fsf@nvdebian.thelocal/

Note: the uffd-wp shmem & hugetlbfs series will need this patch to make
sure swap entries work as expected with below config as spotted by
Alistair:

  !CONFIG_MIGRATION &&
  !CONFIG_MEMORY_FAILURE &&
  !CONFIG_DEVICE_PRIVATE &&
  CONFIG_PTE_MARKER

(PS: this config should mostly never gonna happen, though, afaict..)

Link: https://lkml.kernel.org/r/20220413191147.66645-1-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_alloc: reuse tail struct pages for compound devmaps

Currently memmap_init_zone_device() ends up initializing 32768 pages when
it only needs to initialize 128 given tail page reuse.  That number is
worse with 1GB compound pages, 262144 instead of 128.  Update
memmap_init_zone_device() to skip redundant initialization, detailed
below.

When a pgmap @vmemmap_shift is set, all pages are mapped at a given huge
page alignment and use compound pages to describe them as opposed to a
struct per 4K.

With @vmemmap_shift > 0 and when struct pages are stored in ram (!altmap)
most tail pages are reused.  Consequently, the amount of unique struct
pages is a lot smaller than the total amount of struct pages being mapped.

The altmap path is left alone since it does not support memory savings
based on compound pages devmap.

Link: https://lkml.kernel.org/r/20220420155310.9712-6-joao.m.martins@oracle.com
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/sparse-vmemmap: improve memory savings for compound devmaps

A compound devmap is a dev_pagemap with @vmemmap_shift > 0 and it means
that pages are mapped at a given huge page alignment and utilize uses
compound pages as opposed to order-0 pages.

Take advantage of the fact that most tail pages look the same (except the
first two) to minimize struct page overhead.  Allocate a separate page for
the vmemmap area which contains the head page and separate for the next 64
pages.  The rest of the subsections then reuse this tail vmemmap page to
initialize the rest of the tail pages.

Sections are arch-dependent (e.g.  on x86 it's 64M, 128M or 512M) and when
initializing compound devmap with big enough @vmemmap_shift (e.g.  1G PUD)
it may cross multiple sections.  The vmemmap code needs to consult @pgmap
so that multiple sections that all map the same tail data can refer back
to the first copy of that data for a given gigantic page.

On compound devmaps with 2M align, this mechanism lets 6 pages be saved
out of the 8 necessary PFNs necessary to set the subsection's 512 struct
pages being mapped.  On a 1G compound devmap it saves 4094 pages.

Altmap isn't supported yet, given various restrictions in altmap pfn
allocator, thus fallback to the already in use vmemmap_populate().  It is
worth noting that altmap for devmap mappings was there to relieve the
pressure of inordinate amounts of memmap space to map terabytes of pmem.
With compound pages the motivation for altmaps for pmem gets reduced.

Link: https://lkml.kernel.org/r/20220420155310.9712-5-joao.m.martins@oracle.com
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/hugetlb_vmemmap: move comment block to Documentation/vm

In preparation for device-dax for using hugetlbfs compound page tail
deduplication technique, move the comment block explanation into a common
place in Documentation/vm.

Link: https://lkml.kernel.org/r/20220420155310.9712-4-joao.m.martins@oracle.com
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Suggested-by: Dan Williams <dan.j.williams@intel.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/sparse-vmemmap: refactor core of vmemmap_populate_basepages() to helper

In preparation for describing a memmap with compound pages, move the
actual pte population logic into a separate function
vmemmap_populate_address() and have a new helper vmemmap_populate_range()
walk through all base pages it needs to populate.

While doing that, change the helper to use a pte_t* as return value,
rather than an hardcoded errno of 0 or -ENOMEM.

Link: https://lkml.kernel.org/r/20220420155310.9712-3-joao.m.martins@oracle.com
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/sparse-vmemmap: add a pgmap argument to section activation

Patch series "sparse-vmemmap: memory savings for compound devmaps (device-dax)", v9.

This series minimizes 'struct page' overhead by pursuing a similar
approach as Muchun Song series "Free some vmemmap pages of hugetlb page"
(now merged since v5.14), but applied to devmap with @vmemmap_shift
(device-dax).

The vmemmap dedpulication original idea (already used in HugeTLB) is to
reuse/deduplicate tail page vmemmap areas, particular the area which only
describes tail pages.  So a vmemmap page describes 64 struct pages, and
the first page for a given ZONE_DEVICE vmemmap would contain the head page
and 63 tail pages.  The second vmemmap page would contain only tail pages,
and that's what gets reused across the rest of the subsection/section.
The bigger the page size, the bigger the savings (2M hpage -> save 6
vmemmap pages; 1G hpage -> save 4094 vmemmap pages).

This is done for PMEM /specifically only/ on device-dax configured
namespaces, not fsdax.  In other words, a devmap with a @vmemmap_shift.

In terms of savings, per 1Tb of memory, the struct page cost would go down
with compound devmap:

* with 2M pages we lose 4G instead of 16G (0.39% instead of 1.5% of
  total memory)

* with 1G pages we lose 40MB instead of 16G (0.0014% instead of 1.5% of
  total memory)

The series is mostly summed up by patch 4, and to summarize what the
series does:

Patches 1 - 3: Minor cleanups in preparation for patch 4.  Move the very
nice docs of hugetlb_vmemmap.c into a Documentation/vm/ entry.

Patch 4: Patch 4 is the one that takes care of the struct page savings
(also referred to here as tail-page/vmemmap deduplication).  Much like
Muchun series, we reuse the second PTE tail page vmemmap areas across a
given @vmemmap_shift On important difference though, is that contrary to
the hugetlbfs series, there's no vmemmap for the area because we are
late-populating it as opposed to remapping a system-ram range.  IOW no
freeing of pages of already initialized vmemmap like the case for
hugetlbfs, which greatly simplifies the logic (besides not being
arch-specific).  altmap case unchanged and still goes via the
vmemmap_populate().  Also adjust the newly added docs to the device-dax
case.

[Note that device-dax is still a little behind HugeTLB in terms of
savings.  I have an additional simple patch that reuses the head vmemmap
page too, as a follow-up.  That will double the savings and namespaces
initialization.]

Patch 5: Initialize fewer struct pages depending on the page size with
DRAM backed struct pages -- because fewer pages are unique and most tail
pages (with bigger vmemmap_shift).

    NVDIMM namespace bootstrap improves from ~268-358 ms to
    ~80-110/<1ms on 128G NVDIMMs with 2M and 1G respectivally.  And struct
    page needed capacity will be 3.8x / 1071x smaller for 2M and 1G
    respectivelly.  Tested on x86 with 1.5Tb of pmem (including pinning,
    and RDMA registration/deregistration scalability with 2M MRs)

This patch (of 5):

In support of using compound pages for devmap mappings, plumb the pgmap
down to the vmemmap_populate implementation.  Note that while altmap is
retrievable from pgmap the memory hotplug code passes altmap without
pgmap[*], so both need to be independently plumbed.

So in addition to @altmap, pass @pgmap to sparse section populate
functions namely:

sparse_add_section
  section_activate
    populate_section_memmap
          __populate_section_memmap

Passing @pgmap allows __populate_section_memmap() to both fetch the
vmemmap_shift in which memmap metadata is created for and also to let
sparse-vmemmap fetch pgmap ranges to co-relate to a given section and pick
whether to just reuse tail pages from past onlined sections.

While at it, fix the kdoc for @altmap for sparse_add_section().

[*] https://lore.kernel.org/linux-mm/20210319092635.6214-1-osalvador@suse.de/

Link: https://lkml.kernel.org/r/20220420155310.9712-1-joao.m.martins@oracle.com
Link: https://lkml.kernel.org/r/20220420155310.9712-2-joao.m.martins@oracle.com
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: hugetlb_vmemmap: cleanup CONFIG_HUGETLB_PAGE_FREE_VMEMMAP*

The word of "free" is not expressive enough to express the feature of
optimizing vmemmap pages associated with each HugeTLB, rename this keywork
to "optimize".  In this patch , cheanup configs to make code more
expressive.

Link: https://lkml.kernel.org/r/20220404074652.68024-4-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: hugetlb_vmemmap: cleanup hugetlb_free_vmemmap_enabled*

The word of "free" is not expressive enough to express the feature of
optimizing vmemmap pages associated with each HugeTLB, rename this keywork
to "optimize".  In this patch , cheanup the static key and
hugetlb_free_vmemmap_enabled() to make code more expressive.

Link: https://lkml.kernel.org/r/20220404074652.68024-3-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm: hugetlb_vmemmap: cleanup hugetlb_vmemmap related functions

Patch series "cleanup hugetlb_vmemmap".

The word of "free" is not expressive enough to express the feature of
optimizing vmemmap pages associated with each HugeTLB, rename this keywork
to "optimize" is more clear.  In this series, cheanup related codes to
make it more clear and expressive.  This is suggested by David.

This patch (of 3):

The word of "free" is not expressive enough to express the feature of
optimizing vmemmap pages associated with each HugeTLB, rename this keywork
to "optimize".  And some function names are prefixed with "huge_page"
instead of "hugetlb", it is easily to be confused with THP.  In this
patch, cheanup related functions to make code more clear and expressive.

Link: https://lkml.kernel.org/r/20220404074652.68024-1-songmuchun@bytedance.com
Link: https://lkml.kernel.org/r/20220404074652.68024-2-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_alloc.c: calc the right pfn if page size is not 4K

Previous 0x100000 is used to check the 4G limit in
find_zone_movable_pfns_for_nodes().  This is right in x86 because the page
size can only be 4K.  But 16K and 64K are available in arm64.  So replace
it with PHYS_PFN(SZ_4G).

Link: https://lkml.kernel.org/r/20220414101314.1250667-8-mawupeng1@huawei.com
Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mremap: avoid unneeded do_munmap call

When old_len == new_len, do_munmap will return -EINVAL due to len == 0.
This errno will be simply ignored because of old_len != new_len check.  So
it is unnecessary to call do_munmap when old_len == new_len because
nothing is actually done.

Link: https://lkml.kernel.org/r/20220401081023.37080-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mremap: use helper mlock_future_check()

Use helper mlock_future_check() to check whether it's safe to resize the
locked_vm to simplify the code.  Minor readability improvement.

Link: https://lkml.kernel.org/r/20220322112004.27380-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mmap: drop arch_vm_get_page_pgprot()

There are no platforms left which use arch_vm_get_page_prot(). Just drop
generic arch_vm_get_page_prot().

Link: https://lkml.kernel.org/r/20220414062125.609297-8-anshuman.khandual@arm.com
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mmap: drop arch_filter_pgprot()

There are no platforms left which subscribe ARCH_HAS_FILTER_PGPROT.  Hence
drop generic arch_filter_pgprot() and also config ARCH_HAS_FILTER_PGPROT.

Link: https://lkml.kernel.org/r/20220414062125.609297-7-anshuman.khandual@arm.com
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

x86/mm: enable ARCH_HAS_VM_GET_PAGE_PROT

This defines and exports a platform specific custom vm_get_page_prot() via
subscribing ARCH_HAS_VM_GET_PAGE_PROT.  This also unsubscribes from config
ARCH_HAS_FILTER_PGPROT, after dropping off arch_filter_pgprot() and
arch_vm_get_page_prot().

Link: https://lkml.kernel.org/r/20220414062125.609297-6-anshuman.khandual@arm.com
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: David S. Miller <davem@davemloft.net>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

sparc/mm: enable ARCH_HAS_VM_GET_PAGE_PROT

This defines and exports a platform specific custom vm_get_page_prot() via
subscribing ARCH_HAS_VM_GET_PAGE_PROT.  It localizes
arch_vm_get_page_prot() as sparc_vm_get_page_prot() and moves near
vm_get_page_prot().

Link: https://lkml.kernel.org/r/20220414062125.609297-5-anshuman.khandual@arm.com
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Acked-by: David S. Miller <davem@davemloft.net>
Reviewed-by: Khalid Aziz <khalid.aziz@oracle.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arm64/mm: enable ARCH_HAS_VM_GET_PAGE_PROT

This defines and exports a platform specific custom vm_get_page_prot() via
subscribing ARCH_HAS_VM_GET_PAGE_PROT. It localizes arch_vm_get_page_prot()
and moves it near vm_get_page_prot().

Link: https://lkml.kernel.org/r/20220414062125.609297-4-anshuman.khandual@arm.com
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

powerpc/mm: enable ARCH_HAS_VM_GET_PAGE_PROT

This defines and exports a platform specific custom vm_get_page_prot() via
subscribing ARCH_HAS_VM_GET_PAGE_PROT.  While here, this also localizes
arch_vm_get_page_prot() as __vm_get_page_prot() and moves it near
vm_get_page_prot().

Link: https://lkml.kernel.org/r/20220414062125.609297-3-anshuman.khandual@arm.com
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mmap: add new config ARCH_HAS_VM_GET_PAGE_PROT

Patch series "mm/mmap: Drop arch_vm_get_page_prot() and arch_filter_pgprot()", v7.

protection_map[] is an array based construct that translates given
vm_flags combination.  This array contains page protection map, which is
populated by the platform via [__S000 ..  __S111] and [__P000 ..  __P111]
exported macros.  Primary usage for protection_map[] is for
vm_get_page_prot(), which is used to determine page protection value for a
given vm_flags.  vm_get_page_prot() implementation, could again call
platform overrides arch_vm_get_page_prot() and arch_filter_pgprot().  Some
platforms override protection_map[] that was originally built with
__SXXX/__PXXX with different runtime values.

Currently there are multiple layers of abstraction i.e __SXXX/__PXXX
macros , protection_map[], arch_vm_get_page_prot() and
arch_filter_pgprot() built between the platform and generic MM, finally
defining vm_get_page_prot().

Hence this series proposes to drop later two abstraction levels and
instead just move the responsibility of defining vm_get_page_prot() to the
platform (still utilizing generic protection_map[] array) itself making it
clean and simple.

This first introduces ARCH_HAS_VM_GET_PAGE_PROT which enables the
platforms to define custom vm_get_page_prot().  This starts converting
platforms that define the overrides arch_filter_pgprot() or
arch_vm_get_page_prot() which enables for those constructs to be dropped
off completely.

The series has been inspired from an earlier discuss with Christoph Hellwig

https://lore.kernel.org/all/1632712920-8171-1-git-send-email-anshuman.khandual@arm.com/

This patch (of 7):

Add a new config ARCH_HAS_VM_GET_PAGE_PROT, which when subscribed enables
a given platform to define its own vm_get_page_prot() but still utilizing
the generic protection_map[] array.

Link: https://lkml.kernel.org/r/20220414062125.609297-1-anshuman.khandual@arm.com
Link: https://lkml.kernel.org/r/20220414062125.609297-2-anshuman.khandual@arm.com
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mmap.c: use helper mlock_future_check()

Use helper mlock_future_check() to check whether it's safe to enlarge the
locked_vm to simplify the code.  Minor readability improvement.

Link: https://lkml.kernel.org/r/20220402032231.64974-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mmap: clarify protection_map[] indices

protection_map[] maps vm_flags access combinations into page protection
value as defined by the platform via __PXXX and __SXXX macros.  The array
indices in protection_map[], represents vm_flags access combinations but
it's not very intuitive to derive.  This makes it clear and explicit.

Link: https://lkml.kernel.org/r/20220404031840.588321-3-anshuman.khandual@arm.com
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/debug_vm_pgtable: drop protection_map[] usage

Patch series "mm: protection_map[] cleanups".

This patch (of 2):

Although protection_map[] contains the platform defined page protection
map for a given vm_flags combination, vm_get_page_prot() is the right
interface to use.  This will also reduce dependency on protection_map[]
which is going to be dropped off completely later on.

Link: https://lkml.kernel.org/r/20220404031840.588321-1-anshuman.khandual@arm.com
Link: https://lkml.kernel.org/r/20220404031840.588321-2-anshuman.khandual@arm.com
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mmu_gather: limit free batch count and add schedule point in tlb_batch_pages_flush

free a large list of pages maybe cause rcu_sched starved on
non-preemptible kernels.  howerver free_unref_page_list maybe can't
cond_resched as it maybe called in interrupt or atomic context, especially
can't detect atomic context in CONFIG_PREEMPTION=n.

The issue is detected in guest with kvm cpu 200% overcommit, however I
didn't see the warning in the host with the same application.  I'm sure
that the patch is needed for guest kernel, but no sure for host.

To reproduce, set up two virtual machines in one host machine, per vm has
the same number cpu and half memory of host.  the run ltpstress.sh in per
vm, then will see rcu stall warning.kernel is preempt disabled, append
kernel command 'preempt=none' if enable dynamic preempt .  It could
detected in loongson machine(32 core, 128G mem) and ProLiant DL380
Gen9(x86 E5-2680, 28 core, 64G mem)

tlb flush batch count depends on PAGE_SIZE, it's too large if PAGE_SIZE >
4K, here limit free batch count with 512.  And add schedule point in
tlb_batch_pages_flush.

rcu: rcu_sched kthread starved for 5359 jiffies! g454793 f0x0
RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=19
[...]
Call Trace:
   free_unref_page_list+0x19c/0x270
   release_pages+0x3cc/0x498
   tlb_flush_mmu_free+0x44/0x70
   zap_pte_range+0x450/0x738
   unmap_page_range+0x108/0x240
   unmap_vmas+0x74/0xf0
   unmap_region+0xb0/0x120
   do_munmap+0x264/0x438
   vm_munmap+0x58/0xa0
   sys_munmap+0x10/0x20
   syscall_common+0x24/0x38

Link: https://lkml.kernel.org/r/20220317072857.2635262-1-wangjianxing@loongson.cn
Signed-off-by: Jianxing Wang <wangjianxing@loongson.cn>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mmap.c: use mmap_assert_write_locked() instead of open coding it

In case the lock is actually not held at this point.

Link: https://lkml.kernel.org/r/5827758.TJ1SttVevJ@mobilepool36.emlix.com
Signed-off-by: Rolf Eike Beer <eb@emlix.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

selftests: vm: fix shellcheck warnings in run_vmtests.sh

These might not be issues yet, but they make the script more fragile.
Also by fixing them we give a better example to future readers, who might
copy/paste or otherwise re-use snippets from our script.

- Use "read -r", since we don't ever want read to be interpreting '\'
  characters as escape sequences...
- Quote variables, to deal with spaces properly.
- Use $() instead of the older and harder-to-nest ``.
- Get rid of superfluous "$" prefixes inside arithmetic $(()).

Link: https://lkml.kernel.org/r/20220421224928.1848230-2-axelrasmussen@google.com
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

selftests: vm: refactor run_vmtests.sh to reduce boilerplate

Previously, each test printed out its own header, dealt with its own
return code, etc.  By just putting this standard stuff in a function, we
can delete > 300 lines from the script.

This also makes adding future tests easier. And, it gets rid of various
inconsistencies that already exist:

- Some tests correctly deal with ksft_skip, but others don't.
- Some tests just print the executable name, others print arguments, and
  yet others print some comment in the header.
- Most tests print out a header with two separator lines, but not the
  HMM smoke test or the memfd_secret test, which only print one.
- We had a redundant "exit" at the end, with all the boilerplate it's an
  easy oversight.

Link: https://lkml.kernel.org/r/20220421224928.1848230-1-axelrasmussen@google.com
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

selftests: vm: add test for Soft-Dirty PTE bit

This introduces three tests:

1) Sanity check soft dirty basic semantics: allocate area, clean,
   dirty, check if the SD bit is flipped.

2) Check VMA reuse: validate the VM_SOFTDIRTY usage

3) Check soft-dirty on huge pages

This was motivated by Will Deacon's fix commit 912efa17e512 ("mm: proc:
Invalidate TLB after clearing soft-dirty page state").  I was tracking the
same issue that he fixed, and this test would have caught it.

Link: https://lkml.kernel.org/r/20220420084036.4101604-2-usama.anjum@collabora.com
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Co-developed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Will Deacon <will@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>