Am 11.10.24 um 17:03 schrieb Zi Yan:
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.
Added alloc_zeroed() helper to encapsulate the init_on_alloc check.
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
include/linux/highmem.h | 8 +-------
mm/huge_memory.c | 3 ++-
mm/internal.h | 6 ++++++
mm/memory.c | 3 ++-
4 files changed, 11 insertions(+), 9 deletions(-)
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index bec9bd715acf..6e452bd8e7e3 100644
--- 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 82f464865570..5dcbea96edb7 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1176,7 +1176,8 @@ static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
}
folio_throttle_swaprate(folio, gfp);
- folio_zero_user(folio, addr);
+ if (!alloc_zeroed())
+ folio_zero_user(folio, addr);
It might be reasonable to spell out why we are not using GFP_ZERO somewhere,
something like
/*
* We are not using __GFP_ZERO because folio_zero_user() will make sure that the
* page corresponding to the faulting address will be hot in the cache.
*/
Sth. like that maybe.
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
--
Cheers,
David / dhildenb
