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Message-Id: <20250806145611.3962-1-dev.jain@arm.com>
Date: Wed, 6 Aug 2025 20:26:11 +0530
From: Dev Jain <dev.jain@....com>
To: akpm@...ux-foundation.org
Cc: ryan.roberts@....com,
david@...hat.com,
willy@...radead.org,
linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
catalin.marinas@....com,
will@...nel.org,
Liam.Howlett@...cle.com,
lorenzo.stoakes@...cle.com,
vbabka@...e.cz,
jannh@...gle.com,
anshuman.khandual@....com,
peterx@...hat.com,
joey.gouly@....com,
ioworker0@...il.com,
baohua@...nel.org,
kevin.brodsky@....com,
quic_zhenhuah@...cinc.com,
christophe.leroy@...roup.eu,
yangyicong@...ilicon.com,
linux-arm-kernel@...ts.infradead.org,
hughd@...gle.com,
yang@...amperecomputing.com,
ziy@...dia.com,
Dev Jain <dev.jain@....com>,
syzbot+57bcc752f0df8bb1365c@...kaller.appspotmail.com
Subject: [PATCH mm-hotfixes-unstable] mm: Pass page directly instead of using folio_page
In commit_anon_folio_batch(), we iterate over all pages pointed to by the
PTE batch. Therefore we need to know the first page of the batch;
currently we derive that via folio_page(folio, 0), but, that takes us
to the first (head) page of the folio instead - our PTE batch may lie
in the middle of the folio, leading to incorrectness.
Bite the bullet and throw away the micro-optimization of reusing the
folio in favour of code simplicity. Derive the page and the folio in
change_pte_range, and pass the page too to commit_anon_folio_batch to
fix the aforementioned issue.
Reported-by: syzbot+57bcc752f0df8bb1365c@...kaller.appspotmail.com
Fixes: cac1db8c3aad ("mm: optimize mprotect() by PTE batching")
Signed-off-by: Dev Jain <dev.jain@....com>
---
mm/mprotect.c | 23 ++++++++++-------------
1 file changed, 10 insertions(+), 13 deletions(-)
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 78bded7acf79..113b48985834 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -120,9 +120,8 @@ static int mprotect_folio_pte_batch(struct folio *folio, pte_t *ptep,
static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr,
pte_t oldpte, pte_t *pte, int target_node,
- struct folio **foliop)
+ struct folio *folio)
{
- struct folio *folio = NULL;
bool ret = true;
bool toptier;
int nid;
@@ -131,7 +130,6 @@ static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr,
if (pte_protnone(oldpte))
goto skip;
- folio = vm_normal_folio(vma, addr, oldpte);
if (!folio)
goto skip;
@@ -173,7 +171,6 @@ static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr,
folio_xchg_access_time(folio, jiffies_to_msecs(jiffies));
skip:
- *foliop = folio;
return ret;
}
@@ -231,10 +228,9 @@ static int page_anon_exclusive_sub_batch(int start_idx, int max_len,
* retrieve sub-batches.
*/
static void commit_anon_folio_batch(struct vm_area_struct *vma,
- struct folio *folio, unsigned long addr, pte_t *ptep,
+ struct folio *folio, struct page *first_page, unsigned long addr, pte_t *ptep,
pte_t oldpte, pte_t ptent, int nr_ptes, struct mmu_gather *tlb)
{
- struct page *first_page = folio_page(folio, 0);
bool expected_anon_exclusive;
int sub_batch_idx = 0;
int len;
@@ -251,7 +247,7 @@ static void commit_anon_folio_batch(struct vm_area_struct *vma,
}
static void set_write_prot_commit_flush_ptes(struct vm_area_struct *vma,
- struct folio *folio, unsigned long addr, pte_t *ptep,
+ struct folio *folio, struct page *page, unsigned long addr, pte_t *ptep,
pte_t oldpte, pte_t ptent, int nr_ptes, struct mmu_gather *tlb)
{
bool set_write;
@@ -270,7 +266,7 @@ static void set_write_prot_commit_flush_ptes(struct vm_area_struct *vma,
/* idx = */ 0, set_write, tlb);
return;
}
- commit_anon_folio_batch(vma, folio, addr, ptep, oldpte, ptent, nr_ptes, tlb);
+ commit_anon_folio_batch(vma, folio, page, addr, ptep, oldpte, ptent, nr_ptes, tlb);
}
static long change_pte_range(struct mmu_gather *tlb,
@@ -305,15 +301,19 @@ static long change_pte_range(struct mmu_gather *tlb,
const fpb_t flags = FPB_RESPECT_SOFT_DIRTY | FPB_RESPECT_WRITE;
int max_nr_ptes = (end - addr) >> PAGE_SHIFT;
struct folio *folio = NULL;
+ struct page *page;
pte_t ptent;
+ page = vm_normal_page(vma, addr, oldpte);
+ if (page)
+ folio = page_folio(page);
/*
* Avoid trapping faults against the zero or KSM
* pages. See similar comment in change_huge_pmd.
*/
if (prot_numa) {
int ret = prot_numa_skip(vma, addr, oldpte, pte,
- target_node, &folio);
+ target_node, folio);
if (ret) {
/* determine batch to skip */
@@ -323,9 +323,6 @@ static long change_pte_range(struct mmu_gather *tlb,
}
}
- if (!folio)
- folio = vm_normal_folio(vma, addr, oldpte);
-
nr_ptes = mprotect_folio_pte_batch(folio, pte, oldpte, max_nr_ptes, flags);
oldpte = modify_prot_start_ptes(vma, addr, pte, nr_ptes);
@@ -351,7 +348,7 @@ static long change_pte_range(struct mmu_gather *tlb,
*/
if ((cp_flags & MM_CP_TRY_CHANGE_WRITABLE) &&
!pte_write(ptent))
- set_write_prot_commit_flush_ptes(vma, folio,
+ set_write_prot_commit_flush_ptes(vma, folio, page,
addr, pte, oldpte, ptent, nr_ptes, tlb);
else
prot_commit_flush_ptes(vma, addr, pte, oldpte, ptent,
--
2.30.2
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