linux-kernel - Re: [PATCH v3] mm: thp: fix flags for pmd migration when split

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Date:   Thu, 13 Dec 2018 18:24:57 +0800
From:   Peter Xu <peterx@...hat.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     linux-kernel@...r.kernel.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        Dave Jiang <dave.jiang@...el.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Souptick Joarder <jrdr.linux@...il.com>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Zi Yan <zi.yan@...rutgers.edu>, linux-mm@...ck.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v3] mm: thp: fix flags for pmd migration when split

On Thu, Dec 13, 2018 at 12:59:42PM +0300, Kirill A. Shutemov wrote:
> 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@...hat.com>
> > CC: Andrew Morton <akpm@...ux-foundation.org>
> > CC: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> > CC: Matthew Wilcox <willy@...radead.org>
> > CC: Michal Hocko <mhocko@...e.com>
> > CC: Dave Jiang <dave.jiang@...el.com>
> > CC: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
> > CC: Souptick Joarder <jrdr.linux@...il.com>
> > CC: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
> > CC: Zi Yan <zi.yan@...rutgers.edu>
> > CC: linux-mm@...ck.org
> > CC: linux-kernel@...r.kernel.org
> > Signed-off-by: Peter Xu <peterx@...hat.com>
> 
> Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> 
> Stable?

Sorry I missed the reply from Zi.  I think it should be:

CC: linux-stable <stable@...r.kernel.org> # 4.14+

Thanks,

-- 
Peter Xu