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
