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

[Kirill A. Shutemov]

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@xxxxxxxxxx>
> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> CC: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> CC: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> CC: Michal Hocko <mhocko@xxxxxxxx>
> CC: Dave Jiang <dave.jiang@xxxxxxxxx>
> CC: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> CC: Souptick Joarder <jrdr.linux@xxxxxxxxx>
> CC: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
> CC: Zi Yan <zi.yan@xxxxxxxxxxxxxx>
> CC: linux-mm@xxxxxxxxx
> CC: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>

Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

Stable?

-- 
 Kirill A. Shutemov