From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Will Deacon <will.deacon@arm.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
mark.rutland@arm.com, akpm@linux-foundation.org,
Punit.Agrawal@arm.com, mgorman@suse.de, steve.capper@arm.com
Subject: Re: [PATCH 3/3] mm: migrate: Stabilise page count when migrating transparent hugepages
Date: Thu, 8 Jun 2017 13:47:03 +0300 [thread overview]
Message-ID: <20170608104702.rqrczxh2wcyfril7@black.fi.intel.com> (raw)
In-Reply-To: <1496771916-28203-4-git-send-email-will.deacon@arm.com>
On Tue, Jun 06, 2017 at 06:58:36PM +0100, Will Deacon wrote:
> When migrating a transparent hugepage, migrate_misplaced_transhuge_page
> guards itself against a concurrent fastgup of the page by checking that
> the page count is equal to 2 before and after installing the new pmd.
>
> If the page count changes, then the pmd is reverted back to the original
> entry, however there is a small window where the new (possibly writable)
> pmd is installed and the underlying page could be written by userspace.
> Restoring the old pmd could therefore result in loss of data.
>
> This patch fixes the problem by freezing the page count whilst updating
> the page tables, which protects against a concurrent fastgup without the
> need to restore the old pmd in the failure case (since the page count can
> no longer change under our feet).
>
> Cc: Mel Gorman <mgorman@suse.de>
> Signed-off-by: Will Deacon <will.deacon@arm.com>
Looks correct to me.
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
--
Kirill A. Shutemov
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next prev parent reply other threads:[~2017-06-08 10:47 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-06 17:58 [PATCH 0/3] mm: huge pages: Misc fixes for issues found during fuzzing Will Deacon
2017-06-06 17:58 ` [PATCH 1/3] mm: numa: avoid waiting on freed migrated pages Will Deacon
2017-06-08 9:04 ` Vlastimil Babka
2017-06-08 10:31 ` Mark Rutland
2017-06-08 10:27 ` Kirill A. Shutemov
2017-06-06 17:58 ` [PATCH 2/3] mm/page_ref: Ensure page_ref_unfreeze is ordered against prior accesses Will Deacon
2017-06-08 9:38 ` Vlastimil Babka
2017-06-08 10:34 ` Will Deacon
2017-06-08 11:02 ` Vlastimil Babka
2017-06-08 10:40 ` Kirill A. Shutemov
2017-06-08 11:07 ` Vlastimil Babka
2017-06-08 11:24 ` Will Deacon
2017-06-08 12:16 ` Peter Zijlstra
2017-06-08 12:19 ` Peter Zijlstra
2017-06-08 12:50 ` Peter Zijlstra
2017-06-09 10:05 ` Will Deacon
2017-06-06 17:58 ` [PATCH 3/3] mm: migrate: Stabilise page count when migrating transparent hugepages Will Deacon
2017-06-08 10:47 ` Kirill A. Shutemov [this message]
2017-06-08 10:52 ` Vlastimil Babka
2017-06-08 12:07 ` Will Deacon
2017-06-09 8:25 ` zhong jiang
2017-06-09 9:16 ` zhong jiang
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