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Date:   Fri, 2 Sep 2022 16:35:47 -0400
From:   Peter Xu <peterx@redhat.com>
To:     Alistair Popple <apopple@nvidia.com>
Cc:     linux-mm@kvack.org, akpm@linux-foundation.org,
        Nadav Amit <nadav.amit@gmail.com>,
        huang ying <huang.ying.caritas@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "Sierra Guiza, Alejandro (Alex)" <alex.sierra@amd.com>,
        Felix Kuehling <Felix.Kuehling@amd.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        John Hubbard <jhubbard@nvidia.com>,
        David Hildenbrand <david@redhat.com>,
        Ralph Campbell <rcampbell@nvidia.com>,
        Matthew Wilcox <willy@infradead.org>,
        Karol Herbst <kherbst@redhat.com>,
        Lyude Paul <lyude@redhat.com>, Ben Skeggs <bskeggs@redhat.com>,
        Logan Gunthorpe <logang@deltatee.com>, paulus@ozlabs.org,
        linuxppc-dev@lists.ozlabs.org,
        "Huang, Ying" <ying.huang@intel.com>, stable@vger.kernel.org
Subject: Re: [PATCH v4 1/4] mm/migrate_device.c: Flush TLB while holding PTL
Message-ID: <YxJpIwPn0FGOka0C@xz-m1.local>
References: <9f801e9d8d830408f2ca27821f606e09aa856899.1662078528.git-series.apopple@nvidia.com>
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On Fri, Sep 02, 2022 at 10:35:51AM +1000, Alistair Popple wrote:
> When clearing a PTE the TLB should be flushed whilst still holding the
> PTL to avoid a potential race with madvise/munmap/etc. For example
> consider the following sequence:
> 
>   CPU0                          CPU1
>   ----                          ----
> 
>   migrate_vma_collect_pmd()
>   pte_unmap_unlock()
>                                 madvise(MADV_DONTNEED)
>                                 -> zap_pte_range()
>                                 pte_offset_map_lock()
>                                 [ PTE not present, TLB not flushed ]
>                                 pte_unmap_unlock()
>                                 [ page is still accessible via stale TLB ]
>   flush_tlb_range()
> 
> In this case the page may still be accessed via the stale TLB entry
> after madvise returns. Fix this by flushing the TLB while holding the
> PTL.
> 
> Signed-off-by: Alistair Popple <apopple@nvidia.com>
> Reported-by: Nadav Amit <nadav.amit@gmail.com>
> Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
> Fixes: 8c3328f1f36a ("mm/migrate: migrate_vma() unmap page from vma while collecting pages")
> Cc: stable@vger.kernel.org

Acked-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu