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From:   Muchun Song <songmuchun@bytedance.com>
Date:   Wed, 16 Feb 2022 14:16:13 +0800
Message-ID: <CAMZfGtVQYvqNcNLggUdnbL9oDuYgPhA40caTV2afwmtSgzJCRg@mail.gmail.com>
Subject: Re: [PATCH v5 5/7] mm: shmem: fix missing cache flush in shmem_mfill_atomic_pte()
To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, zi.yan@cs.rutgers.edu,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Lars Persson <lars.persson@axis.com>, Zi Yan <ziy@nvidia.com>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Xiongchun duan <duanxiongchun@bytedance.com>,
        Fam Zheng <fam.zheng@bytedance.com>
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On Wed, Feb 16, 2022 at 3:12 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 2/10/22 04:30, Muchun Song wrote:
> > The userfaultfd calls shmem_mfill_atomic_pte() which does not do any
> > cache flushing for the target page.  Then the target page will be mapped
> > to the user space with a different address (user address), which might
> > have an alias issue with the kernel address used to copy the data from the
> > user to.  Insert flush_dcache_page() in non-zero-page case.  And replace
> > clear_highpage() with clear_user_highpage() which already considers
> > the cache maintenance.
> >
> > Fixes: 8d1039634206 ("userfaultfd: shmem: add shmem_mfill_zeropage_pte for userfaultfd support")
> > Fixes: 4c27fe4c4c84 ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support")
> > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> > ---
> >  mm/shmem.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
>
> Thanks,
>
> It might have been better to combine this and the next patch.  When looking
> at this, I noted the 'fallback to copy_from_user outside mmap_lock' case needs
> to be addressed as well.  It is in the next patch.  No need to change.

I separate those changes into 2 patches since the fixed patch
is different. This patch is fixing linux 4.13 and later, while next
patch is fixing linux 4.2 and later. Maybe it is hard to backport
if combining those two patches.

>
> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>

Thanks Mike.