From: Andrew Morton <akpm@linux-foundation.org>
To: jglisse@redhat.com
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Ralph Campbell <rcampbell@nvidia.com>
Subject: Re: [PATCH] mm/migrate: properly preserve write attribute in special migrate entry
Date: Tue, 3 Apr 2018 15:30:46 -0700 [thread overview]
Message-ID: <20180403153046.88cae4ab18646e8e23a648ce@linux-foundation.org> (raw)
In-Reply-To: <20180402023506.12180-1-jglisse@redhat.com>
On Sun, 1 Apr 2018 22:35:06 -0400 jglisse@redhat.com wrote:
> From: Ralph Campbell <rcampbell@nvidia.com>
>
> Use of pte_write(pte) is only valid for present pte, the common code
> which set the migration entry can be reach for both valid present
> pte and special swap entry (for device memory). Fix the code to use
> the mpfn value which properly handle both cases.
>
> On x86 this did not have any bad side effect because pte write bit
> is below PAGE_BIT_GLOBAL and thus special swap entry have it set to
> 0 which in turn means we were always creating read only special
> migration entry.
Does this mean that the patch only affects behaviour of non-x86 systems?
> So once migration did finish we always write protected the CPU page
> table entry (moreover this is only an issue when migrating from device
> memory to system memory). End effect is that CPU write access would
> fault again and restore write permission.
That sounds a bit serious. Was a -stable backport considered?
next prev parent reply other threads:[~2018-04-03 22:30 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-02 2:35 [PATCH] mm/migrate: properly preserve write attribute in special migrate entry jglisse
2018-04-03 22:30 ` Andrew Morton [this message]
2018-04-03 23:03 ` Jerome Glisse
2018-04-03 23:45 ` Andrew Morton
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