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SubjectRe: [PATCH] mm,do_huge_pmd_numa_page: remove unnecessary TLB flushing code
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On 22.07.21 02:26, Huang, Ying wrote:
> Sean Christopherson <seanjc@google.com> writes:
>>>
>>> Thanks, I think you are correct. By looking into commit 7066f0f933a1
>>> ("mm: thp: fix mmu_notifier in migrate_misplaced_transhuge_page()"),
>>> the tlb flush and mmu notifier invalidate were needed since the old
>>> numa fault implementation didn't change PTE to migration entry so it
>>> may cause data corruption due to the writes from GPU secondary MMU.
>>>
>>> The refactor does use the generic migration code which converts PTE to
>>> migration entry before copying data to the new page.
>>
>> That's my understanding as well, based on this blurb from commit 7066f0f933a1.
>>
>> The standard PAGE_SIZEd migrate_misplaced_page is less accelerated and
>> uses the generic migrate_pages which transitions the pte from
>> numa/protnone to a migration entry in try_to_unmap_one() and flushes TLBs
>> and all mmu notifiers there before copying the page.
>>
>> That analysis/justification for removing the invalidate_range() call should be
>> captured in the changelog. Confirmation from Andrea would be a nice bonus.
>
> When we flush CPU TLB for a page that may be shared with device/VM TLB,
> we will call MMU notifiers for the page to flush the device/VM TLB.
> Right? So when we replaced CPU TLB flushing in do_huge_pmd_numa_page()
> with that in try_to_migrate_one(), we will replace the MMU notifiers
> calling too. Do you agree?

Can someone write an updated commit messages that contains this information?

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