linux-kernel - Re: [PATCH v1 2/3] mm/gup: use gup_can_follow

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Message-ID: <0aba2bfc-9f10-2fb1-1858-d8eb04b5d52e@redhat.com>
Date:   Wed, 31 Aug 2022 21:25:22 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     John Hubbard <jhubbard@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Alistair Popple <apopple@...dia.com>
Subject: Re: [PATCH v1 2/3] mm/gup: use gup_can_follow_protnone() also in
 GUP-fast

>>>> 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