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

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Date:   Thu, 01 Sep 2022 17:55:58 +1000
From:   Alistair Popple <apopple@...dia.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Peter Xu <peterx@...hat.com>, 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>
Subject: Re: [PATCH v1 2/3] mm/gup: use gup_can_follow_protnone() also in
 GUP-fast


David Hildenbrand <david@...hat.com> writes:

>>>>> 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,
>>

Thanks for the heads up. I'm still digesting this thread but I do plan
on fixing that up in my series which I hope to post an updated version
of tomorrow.

> 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.

Yeah, probably best if we can rebase this on my fix-up series.

> Thanks!