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Subject: Re: [PATCH] mm,do_huge_pmd_numa_page: remove unnecessary TLB flushing
 code
To:     "Huang, Ying" <ying.huang@intel.com>,
        Sean Christopherson <seanjc@google.com>
Cc:     Yang Shi <shy828301@gmail.com>, Zi Yan <ziy@nvidia.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Mel Gorman <mgorman@suse.de>,
        Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Hugh Dickins <hughd@google.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Michal Hocko <mhocko@suse.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        kvm list <kvm@vger.kernel.org>
References: <20210720065529.716031-1-ying.huang@intel.com>
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 <CAHbLzkp6LDLUK9TLM+geQM6+X6+toxAGi53UBd49Zm5xgc5aWQ@mail.gmail.com>
 <0D75A92F-E2AA-480C-9E9A-0B6EE7897757@nvidia.com>
 <CAHbLzkqZZEic7+H0ky9u+aKO5o_cF0N5xQ=JO2tMpc8jg8RcnQ@mail.gmail.com>
 <YPhAEcHOCZ5yII/T@google.com>
 <87lf5z9osl.fsf@yhuang6-desk2.ccr.corp.intel.com>
From:   Christian Borntraeger <borntraeger@de.ibm.com>
Message-ID: <572f1ddd-9ac6-fb09-9a24-1c667dbd1d03@de.ibm.com>
Date:   Thu, 22 Jul 2021 09:36:07 +0200
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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?