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Message-ID: <78922f87-dc5c-4652-a5c3-869d1bca1d88@arm.com>
Date: Wed, 6 Aug 2025 22:49:46 +0530
From: Dev Jain <dev.jain@....com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: akpm@...ux-foundation.org, 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,
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,
syzbot+57bcc752f0df8bb1365c@...kaller.appspotmail.com
Subject: Re: [PATCH mm-hotfixes-unstable] mm: Pass page directly instead of
using folio_page
On 06/08/25 10:10 pm, Lorenzo Stoakes wrote:
> On Wed, Aug 06, 2025 at 08:26:11PM +0530, Dev Jain wrote:
>> 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>
> This looks reasonable, fixes the problem and compiles/works on my machine so:
>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Thanks.
>
> This badly needs refactoring as 13 parameters being passed to a function is
Which function are you talking about?
> ridiculous, but we can do that later.
>
> Let's get this in as a hotfix asap.
>
>> ---
>> 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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