From: Peter Xu peterx@redhat.com Subject: mm: thp: fix flags for pmd migration when split

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.

Link: http://lkml.kernel.org/r/20181213051510.20306-1-peterx@redhat.com Signed-off-by: Peter Xu peterx@redhat.com Reviewed-by: Konstantin Khlebnikov khlebnikov@yandex-team.ru Reviewed-by: William Kucharski william.kucharski@oracle.com Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Andrea Arcangeli aarcange@redhat.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: stable@vger.kernel.org [4.14+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/huge_memory.c | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-)

--- a/mm/huge_memory.c~mm-thp-fix-flags-for-pmd-migration-when-split +++ a/mm/huge_memory.c @@ -2144,23 +2144,25 @@ static void __split_huge_pmd_locked(stru */ old_pmd = pmdp_invalidate(vma, haddr, pmd);

-#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION pmd_migration = is_pmd_migration_entry(old_pmd); - if (pmd_migration) { + if (unlikely(pmd_migration)) { swp_entry_t entry;

entry = pmd_to_swp_entry(old_pmd); page = pfn_to_page(swp_offset(entry)); - } else -#endif + write = is_write_migration_entry(entry); + young = false; + soft_dirty = pmd_swp_soft_dirty(old_pmd); + } else { page = pmd_page(old_pmd); + if (pmd_dirty(old_pmd)) + SetPageDirty(page); + write = pmd_write(old_pmd); + young = pmd_young(old_pmd); + soft_dirty = pmd_soft_dirty(old_pmd); + } VM_BUG_ON_PAGE(!page_count(page), page); page_ref_add(page, HPAGE_PMD_NR - 1); - if (pmd_dirty(old_pmd)) - SetPageDirty(page); - write = pmd_write(old_pmd); - young = pmd_young(old_pmd); - soft_dirty = pmd_soft_dirty(old_pmd);

/* * Withdraw the table only after we mark the pmd entry invalid. _