On 19/05/2023 00:19, Yu Zhao wrote:
> On Thu, May 18, 2023 at 5:07 AM Ryan Roberts <ryan.roberts@xxxxxxx> wrote:
>>
>> It is racy to non-atomically read a pte, then clear the young bit, then
>> write it back as this could discard dirty information. Further, it is
>> bad practice to directly set a pte entry within a table. Instead
>> clearing young must go through the arch-provided helper,
>> ptep_test_and_clear_young() to ensure it is modified atomically and to
>> give the arch code visibility and allow it to check (and potentially
>> modify) the operation.
>>
>> Fixes: 46c3a0accdc4 ("mm/damon/vaddr: separate commonly usable functions")
>
> This should be a separate patch, since it's independent from what the
> series tries to do.
>
> And that patch should cc stable, since it fixes user data corruption.
Fair point. The first 3 patches are fixes for issues I found during the
conversion. So if you're ok with it, I'll split into 2 series; the first 3
patches in the first, and the conversion to ptep_deref() (or ptep_get(), as per
your comments in the other thread) in the second. I guess the whole first series
should go to stable.
Let me know if you disagree.
>
>> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
>> Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
>> ---
>> mm/damon/ops-common.c | 16 ++++++----------
>> mm/damon/ops-common.h | 4 ++--
>> mm/damon/paddr.c | 4 ++--
>> mm/damon/vaddr.c | 4 ++--
>> 4 files changed, 12 insertions(+), 16 deletions(-)
>>
>> diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
>> index cc63cf953636..acc264b97903 100644
>> --- a/mm/damon/ops-common.c
>> +++ b/mm/damon/ops-common.c
>> @@ -37,7 +37,7 @@ struct folio *damon_get_folio(unsigned long pfn)
>> return folio;
>> }
>>
>> -void damon_ptep_mkold(pte_t *pte, struct mm_struct *mm, unsigned long addr)
>> +void damon_ptep_mkold(pte_t *pte, struct vm_area_struct *vma, unsigned long addr)
>> {
>> bool referenced = false;
>> struct folio *folio = damon_get_folio(pte_pfn(*pte));
>> @@ -45,13 +45,11 @@ void damon_ptep_mkold(pte_t *pte, struct mm_struct *mm, unsigned long addr)
>> if (!folio)
>> return;
>>
>> - if (pte_young(*pte)) {
>> + if (ptep_test_and_clear_young(vma, addr, pte))
>> referenced = true;
>> - *pte = pte_mkold(*pte);
>> - }
>>
>> #ifdef CONFIG_MMU_NOTIFIER
>> - if (mmu_notifier_clear_young(mm, addr, addr + PAGE_SIZE))
>> + if (mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE))
>> referenced = true;
>> #endif /* CONFIG_MMU_NOTIFIER */
>
> Use ptep_clear_young_notify(). Similar below.
This looks sensible but I'd like clarification from SeongJae: Are you happy for
me to do this refactoring as part of the patch?
Thanks,
Ryan
