Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:37384 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725807AbeLUWaw (ORCPT ); Fri, 21 Dec 2018 17:30:52 -0500 Date: Fri, 21 Dec 2018 14:30:50 -0800 From: akpm@linux-foundation.org To: zi.yan@cs.rutgers.edu, willy@infradead.org, william.kucharski@oracle.com, stable@vger.kernel.org, mhocko@suse.com, kirill.shutemov@linux.intel.com, khlebnikov@yandex-team.ru, jrdr.linux@gmail.com, dave.jiang@intel.com, aneesh.kumar@linux.vnet.ibm.com, aarcange@redhat.com, peterx@redhat.com, akpm@linux-foundation.org, mm-commits@vger.kernel.org, torvalds@linux-foundation.org Subject: [patch 2/4] mm: thp: fix flags for pmd migration when split Message-ID: <20181221223050.z0fCv%akpm@linux-foundation.org> Sender: stable-owner@vger.kernel.org List-ID: From: Peter Xu 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 Reviewed-by: Konstantin Khlebnikov Reviewed-by: William Kucharski Acked-by: Kirill A. Shutemov Cc: Andrea Arcangeli Cc: Matthew Wilcox Cc: Michal Hocko Cc: Dave Jiang Cc: "Aneesh Kumar K.V" Cc: Souptick Joarder Cc: Konstantin Khlebnikov Cc: Zi Yan Cc: [4.14+] Signed-off-by: Andrew Morton --- 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. _