linux-kernel - Re: [PATCH v2 2/2] mm/rmap: Fixup copying of soft dirty and uffd ptes

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Message-ID: <20200825144203.GA8235@xz-x1>
Date:   Tue, 25 Aug 2020 10:42:03 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Alistair Popple <alistair@...ple.id.au>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Ralph Campbell <rcampbell@...dia.com>, stable@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mm/rmap: Fixup copying of soft dirty and uffd ptes

On Tue, Aug 25, 2020 at 04:42:32PM +1000, Alistair Popple wrote:
> During memory migration a pte is temporarily replaced with a migration
> swap pte. Some pte bits from the existing mapping such as the soft-dirty
> and uffd write-protect bits are preserved by copying these to the
> temporary migration swap pte.
> 
> However these bits are not stored at the same location for swap and
> non-swap ptes. Therefore testing these bits requires using the
> appropriate helper function for the given pte type.
> 
> Unfortunately several code locations were found where the wrong helper
> function is being used to test soft_dirty and uffd_wp bits which leads
> to them getting incorrectly set or cleared during page-migration.
> 
> Fix these by using the correct tests based on pte type.
> 
> Fixes: a5430dda8a3a ("mm/migrate: support un-addressable ZONE_DEVICE page in migration")
> Fixes: 8c3328f1f36a ("mm/migrate: migrate_vma() unmap page from vma while collecting pages")
> Fixes: f45ec5ff16a7 ("userfaultfd: wp: support swap and page migration")
> Signed-off-by: Alistair Popple <alistair@...ple.id.au>
> Cc: stable@...r.kernel.org

Reviewed-by: Peter Xu <peterx@...hat.com>

-- 
Peter Xu