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Date: Thu, 13 Dec 2018 12:59:42 +0300
From: "Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: [PATCH v3] mm: thp: fix flags for pmd migration when split
Message-ID: <20181213095942.3y7lfdwndek6sja4@kshutemo-mobl1>
References: <20181213051510.20306-1-peterx@redhat.com>
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To: Peter Xu <peterx@redhat.com>
Cc: linux-kernel@vger.kernel.org, Andrea Arcangeli <aarcange@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Matthew Wilcox <willy@infradead.org>, Michal Hocko <mhocko@suse.com>, Dave Jiang <dave.jiang@intel.com>, "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>, Souptick Joarder <jrdr.linux@gmail.com>, Konstantin Khlebnikov <khlebnikov@yandex-team.ru>, Zi Yan <zi.yan@cs.rutgers.edu>, linux-mm@kvack.org

On Thu, Dec 13, 2018 at 01:15:10PM +0800, Peter Xu wrote:
> When splitting a huge migrating PMD, we'll transfer all the existing
> PMD bits and apply them again onto the small PTEs.  However we are
> fetching the bits unconditionally via pmd_soft_dirty(), pmd_write()
> or pmd_yound() while actually they don't make sense at all when it's
> a migration entry.  Fix them up.  Since at it, drop the ifdef together
> as not needed.
> 
> Note that if my understanding is correct about the problem then if
> without the patch there is chance to lose some of the dirty bits in
> the migrating pmd pages (on x86_64 we're fetching bit 11 which is part
> of swap offset instead of bit 2) and it could potentially corrupt the
> memory of an userspace program which depends on the dirty bit.
> 
> CC: Andrea Arcangeli <aarcange@redhat.com>
> CC: Andrew Morton <akpm@linux-foundation.org>
> CC: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> CC: Matthew Wilcox <willy@infradead.org>
> CC: Michal Hocko <mhocko@suse.com>
> CC: Dave Jiang <dave.jiang@intel.com>
> CC: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
> CC: Souptick Joarder <jrdr.linux@gmail.com>
> CC: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> CC: Zi Yan <zi.yan@cs.rutgers.edu>
> CC: linux-mm@kvack.org
> CC: linux-kernel@vger.kernel.org
> Signed-off-by: Peter Xu <peterx@redhat.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

Stable?

-- 
 Kirill A. Shutemov