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

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Commit 6471384af2 ("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>
This commit is contained in:
Zi Yan 2024-10-11 11:03:04 -04:00 committed by Andrew Morton
parent 773ee2cda5
commit 5708d96da2
4 changed files with 23 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
include/linux/highmem.h
View File

@ -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

8
mm/huge_memory.c
View File

@ -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()

6
mm/internal.h
View File

@ -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,

10
mm/memory.c
View File

@ -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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