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SubjectRe: [PATCH] mm/damon: Validate if the pmd entry is present before accessing
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在 8/18/2022 10:41 AM, Muchun Song 写道:
>
>
>> On Aug 17, 2022, at 14:21, Baolin Wang <baolin.wang@linux.alibaba.com> wrote:
>>
>> The pmd_huge() is used to validate if the pmd entry is mapped by a huge
>> page, also including the case of non-present (migration or hwpoisoned)
>> pmd entry on arm64 or x86 architectures. Thus we should validate if it
>> is present before making the pmd entry old or getting young state,
>> otherwise we can not get the correct corresponding page.
>>
>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
>> ---
>> mm/damon/vaddr.c | 10 ++++++++++
>> 1 file changed, 10 insertions(+)
>>
>> diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
>> index 3c7b9d6..1d16c6c 100644
>> --- a/mm/damon/vaddr.c
>> +++ b/mm/damon/vaddr.c
>> @@ -304,6 +304,11 @@ static int damon_mkold_pmd_entry(pmd_t *pmd, unsigned long addr,
>>
>> if (pmd_huge(*pmd)) {
>> ptl = pmd_lock(walk->mm, pmd);
>> + if (!pmd_present(*pmd)) {
>
> Unluckily, we should use pte_present here. See commit c9d398fa23788. We can use
> huge_ptep_get() to get a hugetlb pte, so it’s better to put the check after
> pmd_huge.

IMO this is not the case for hugetlb, and the hugetlb case will be
handled by damon_mkold_hugetlb_entry(), which already used pte_present()
for hugetlb case.

>
> Cc Mike to make sure I am not missing something.
>
> Muchun,
> Thanks.
>
>> + spin_unlock(ptl);
>> + return 0;
>> + }
>> +
>> if (pmd_huge(*pmd)) {
>> damon_pmdp_mkold(pmd, walk->mm, addr);
>> spin_unlock(ptl);
>> @@ -431,6 +436,11 @@ static int damon_young_pmd_entry(pmd_t *pmd, unsigned long addr,
>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> if (pmd_huge(*pmd)) {
>> ptl = pmd_lock(walk->mm, pmd);
>> + if (!pmd_present(*pmd)) {
>> + spin_unlock(ptl);
>> + return 0;
>> + }
>> +
>> if (!pmd_huge(*pmd)) {
>> spin_unlock(ptl);
>> goto regular_page;
>> --
>> 1.8.3.1
>>
>>
>

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