linux-kernel - Re: [PATCH v4 1/4] mm/migrate_device.c: Flush TLB while holding PTL

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Message-ID: <YxJpIwPn0FGOka0C@xz-m1.local>
Date:   Fri, 2 Sep 2022 16:35:47 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Alistair Popple <apopple@...dia.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        Nadav Amit <nadav.amit@...il.com>,
        huang ying <huang.ying.caritas@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "Sierra Guiza, Alejandro (Alex)" <alex.sierra@....com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Jason Gunthorpe <jgg@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        David Hildenbrand <david@...hat.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Matthew Wilcox <willy@...radead.org>,
        Karol Herbst <kherbst@...hat.com>,
        Lyude Paul <lyude@...hat.com>, Ben Skeggs <bskeggs@...hat.com>,
        Logan Gunthorpe <logang@...tatee.com>, paulus@...abs.org,
        linuxppc-dev@...ts.ozlabs.org,
        "Huang, Ying" <ying.huang@...el.com>, stable@...r.kernel.org
Subject: Re: [PATCH v4 1/4] mm/migrate_device.c: Flush TLB while holding PTL

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@...dia.com>
> Reported-by: Nadav Amit <nadav.amit@...il.com>
> Reviewed-by: "Huang, Ying" <ying.huang@...el.com>
> Fixes: 8c3328f1f36a ("mm/migrate: migrate_vma() unmap page from vma while collecting pages")
> Cc: stable@...r.kernel.org

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

-- 
Peter Xu