arm64: add support for sub-page faults user probing

arm64: add support for sub-page faults user probing

With MTE, even if the pte allows an access, a mismatched tag somewhere
within a page can still cause a fault.  Select ARCH_HAS_SUBPAGE_FAULTS if
MTE is enabled and implement probe_user_writeable().

Link: https://lkml.kernel.org/r/20211124192024.2408218-3-catalin.marinas@arm.com
Fixes: a48b73eca4ce ("btrfs: fix potential deadlock in the search ioctl")
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: David Sterba <dsterba@suse.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Will Deacon <will@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>