linux-kernel - Re: [PATCH v1 0/2] mm/hugetlb: uffd-wp fixes for hugetlb_change

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Date:   Thu, 22 Dec 2022 16:28:10 -0500
From:   Peter Xu <peterx@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Miaohe Lin <linmiaohe@...wei.com>
Subject: Re: [PATCH v1 0/2] mm/hugetlb: uffd-wp fixes for
 hugetlb_change_protection()

On Thu, Dec 22, 2022 at 04:17:22PM -0500, Peter Xu wrote:
> On Thu, Dec 22, 2022 at 09:55:09PM +0100, David Hildenbrand wrote:
> > Playing with virtio-mem and background snapshots (using uffd-wp) on
> > hugetlb in QEMU, I managed to trigger a VM_BUG_ON(). Looking into the
> > details, hugetlb_change_protection() seems to not handle uffd-wp correctly
> > in all cases.
> > 
> > Patch #1 fixes my test case. I don't have reproducers for patch #2, as
> > it requires running into migration entries.
> > 
> > I did not yet check in detail yet if !hugetlb code requires similar care.

Ah I should have left a message here but I forgot - afaict shmem is all fine.

> > 
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Mike Kravetz <mike.kravetz@...cle.com>
> > Cc: Peter Xu <peterx@...hat.com>
> > Cc: Muchun Song <muchun.song@...ux.dev>
> > Cc: Miaohe Lin <linmiaohe@...wei.com>
> > 
> > David Hildenbrand (2):
> >   mm/hugetlb: fix PTE marker handling in hugetlb_change_protection()
> >   mm/hugetlb: fix uffd-wp handling for migration entries in
> >     hugetlb_change_protection()
> 
> Reviewed-by: Peter Xu <peterx@...hat.com>
> 
> Thanks, David.
> 
> -- 
> Peter Xu

-- 
Peter Xu