Messages in this thread | | | Date | Sun, 21 Aug 2022 13:54:37 +0800 | Subject | Re: [PATCH 0/3] Fix some issues when looking up hugetlb page | From | Baolin Wang <> |
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On 8/20/2022 8:08 AM, Mike Kravetz wrote: > On 08/19/22 18:12, Baolin Wang wrote: >> Hi, >> >> On ARM64 architecture, it can support CONT-PTE/PMD size hugetlb. When >> looking up hugetlb page by follow_page(), we will hold the incorrect >> pte/pmd lock for the CONT-PTE/PMD size hugetlb page, which will make >> the pte/pmd entry unstable even under the lock and cause some potential >> race issues. So considering the CONT-PTE/PMD size hugetlb, this patch set >> changes to use the correct function to get the correct pte/pmd entry lock >> to make the pte/pmd entry stable. > > Thank you for looking at this. > > I often get confused by arm64 CONT-PTE/PMD layout, so my understanding may be > wrong. Can we use the PMD page lock for locking both CONT-PTE and CONT-PMD > entries? Again, I may be confused by the CONT-* page table layout, but it > seems these would all be referenced via that same PMD page of the page table. > Or, perhaps CONT-PMD can span multiple PMD pages?
Good point. CONT-PMD can not span multiple PMD pages, so I think CONT-PMD can use PMD pagetable page lock, but CONT-PTE also can not span multiple PTE pagetable page lock, so I think CONT-PTE can use the PTE pagetable page lock to get a fine grained lock.
I will add CONT-PTE and CONT-PMD case in huge_pte_lockptr() in next version. Thanks for your comment.
> If we can use PMD page for locking, this would be much finer grain that > lock in the mm.
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