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@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?

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

CC: linux-stable stable@vger.kernel.org # 4.14+

Thanks,