mm: avoid zeroing user movable page twice with init_on_alloc=1

Commit 6471384af2a6 ("mm: security: introduce init_on_alloc=1 and
init_on_free=1 boot options") forces allocated page to be zeroed in
post_alloc_hook() when init_on_alloc=1.

For order-0 folios, if arch does not define
vma_alloc_zeroed_movable_folio(), the default implementation again zeros
the page return from the buddy allocator.  So the page is zeroed twice.
Fix it by passing __GFP_ZERO instead to avoid double page zeroing.  At the
moment, s390,arm64,x86,alpha,m68k are not impacted since they define their
own vma_alloc_zeroed_movable_folio().

For >0 order folios (mTHP and PMD THP), folio_zero_user() is called to
zero the folio again.  Fix it by calling folio_zero_user() only if
init_on_alloc is set.  All arch are impacted.

Add alloc_zeroed() helper to encapsulate the init_on_alloc check.

[ziy@nvidia.com: comment fixes, per David]
Link: https://lkml.kernel.org/r/97DB52E1-C594-49B5-9736-89AC302FAB01@nvidia.com
Link: https://lkml.kernel.org/r/20241011150304.709590-1-ziy@nvidia.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index bec9bd715acf91cb41988464669635794f9bcfa8..6e452bd8e7e364946764e0da3d5363ee2e109349 100644 (file)
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -224,13 +224,7 @@ static inline
 struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
                                   unsigned long vaddr)
 {
-       struct folio *folio;
-
-       folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, vaddr);
-       if (folio)
-               clear_user_highpage(&folio->page, vaddr);
-
-       return folio;
+       return vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, 0, vma, vaddr);
 }
 #endif
 

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 387c046a389e73182a2c38b8a0f3d9b06763255d..73194aa0544cec00d43f3d91c1b4f02dbaac51f6 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1162,7 +1162,13 @@ static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
        }
        folio_throttle_swaprate(folio, gfp);
 
-       folio_zero_user(folio, addr);
+       /*
+       * When a folio is not zeroed during allocation (__GFP_ZERO not used),
+       * folio_zero_user() is used to make sure that the page corresponding
+       * to the faulting address will be hot in the cache after zeroing.
+       */
+       if (!alloc_zeroed())
+               folio_zero_user(folio, addr);
        /*
         * The memory barrier inside __folio_mark_uptodate makes sure that
         * folio_zero_user writes become visible before the set_pmd_at()

diff --git a/mm/internal.h b/mm/internal.h
index fc2f523258a368d3654682fd2a9518ee75d61a41..c743c2b21dbacb4d47068a2de18d9f350cb73f4e 100644 (file)
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1276,6 +1276,12 @@ void touch_pud(struct vm_area_struct *vma, unsigned long addr,
 void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
               pmd_t *pmd, bool write);
 
+static inline bool alloc_zeroed(void)
+{
+       return static_branch_maybe(CONFIG_INIT_ON_ALLOC_DEFAULT_ON,
+                       &init_on_alloc);
+}
+
 enum {
        /* mark page accessed */
        FOLL_TOUCH = 1 << 16,

diff --git a/mm/memory.c b/mm/memory.c
index c51bc45a70099533afccb982553d6072dca278cc..68e57b33363b4e8e83e4f1dcc13c287159458168 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4719,7 +4719,15 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
                                goto next;
                        }
                        folio_throttle_swaprate(folio, gfp);
-                       folio_zero_user(folio, vmf->address);
+                       /*
+                        * When a folio is not zeroed during allocation
+                        * (__GFP_ZERO not used), folio_zero_user() is used
+                        * to make sure that the page corresponding to the
+                        * faulting address will be hot in the cache after
+                        * zeroing.
+                        */
+                       if (!alloc_zeroed())
+                               folio_zero_user(folio, vmf->address);
                        return folio;
                }
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