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Date:   Wed, 31 Aug 2022 21:25:22 +0200
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Subject: Re: [PATCH v1 2/3] mm/gup: use gup_can_follow_protnone() also in
 GUP-fast
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To:     Peter Xu <peterx@redhat.com>
Cc:     John Hubbard <jhubbard@nvidia.com>,
        Jason Gunthorpe <jgg@nvidia.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Hugh Dickins <hughd@google.com>,
        Alistair Popple <apopple@nvidia.com>
References: <20220825164659.89824-1-david@redhat.com>
 <20220825164659.89824-3-david@redhat.com>
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 <Yw5a1paQJ9MNdgmW@nvidia.com>
 <9ce3aaaa-71a6-5a81-16a3-36e6763feb91@redhat.com>
 <9a4fe603-950e-785b-6281-2e309256463f@nvidia.com>
 <68b38ac4-c680-b694-21a9-1971396d63b9@redhat.com>
 <Yw+KnRTrZ74qFUAA@xz-m1.local>
 <4d067a99-1112-3b3d-bedf-35c1124904fd@redhat.com>
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From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <Yw+nFBgnSH9WWYHv@xz-m1.local>
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>>>> diff --git a/mm/ksm.c b/mm/ksm.c
>>>> index d7526c705081..971cf923c0eb 100644
>>>> --- a/mm/ksm.c
>>>> +++ b/mm/ksm.c
>>>> @@ -1091,6 +1091,7 @@ static int write_protect_page(struct vm_area_struct *vma, struct page *page,
>>>>  			goto out_unlock;
>>>>  		}
>>>>  
>>>> +		/* See page_try_share_anon_rmap(): clear PTE first. */
>>>>  		if (anon_exclusive && page_try_share_anon_rmap(page)) {
>>>>  			set_pte_at(mm, pvmw.address, pvmw.pte, entry);
>>>>  			goto out_unlock;
>>>> diff --git a/mm/migrate_device.c b/mm/migrate_device.c
>>>> index 27fb37d65476..47e955212f15 100644
>>>> --- a/mm/migrate_device.c
>>>> +++ b/mm/migrate_device.c
>>>> @@ -193,20 +193,16 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
>>>>  			bool anon_exclusive;
>>>>  			pte_t swp_pte;
>>>>  
>>>
>>> flush_cache_page() missing here?
>>
>> Hmm, wouldn't that already be missing on the !anon path right now?
> 
> Yes, I think Alistair plans to fix it too in the other patchset.  So either
> this will rebase to that or it should fix it too.  Thanks,
> 

I'll include it in this patch for now, because by dropping it I would
make the situation "worse". But most probably we want a separate fix
upfront that we can properly backport to older kernels.

Thanks!

-- 
Thanks,

David / dhildenb