linux-kernel - [HELP-NEEDED, PATCH 0/3] Do not loose dirty bit on THP pages

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Message-Id: <20170614135143.25068-1-kirill.shutemov@linux.intel.com>
Date:   Wed, 14 Jun 2017 16:51:40 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vineet Gupta <vgupta@...opsys.com>,
        Russell King <linux@...linux.org.uk>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        "David S. Miller" <davem@...emloft.net>,
        Heiko Carstens <heiko.carstens@...ibm.com>
Cc:     "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [HELP-NEEDED, PATCH 0/3] Do not loose dirty bit on THP pages

Hi,

Vlastimil noted that pmdp_invalidate() is not atomic and we can loose
dirty and access bits if CPU sets them after pmdp dereference, but
before set_pmd_at().

The bug doesn't lead to user-visible misbehaviour in current kernel, but
fixing this would be critical for future work on THP: both huge-ext4 and THP
swap out rely on proper dirty tracking.

Unfortunately, there's no way to address the issue in a generic way. We need to
fix all architectures that support THP one-by-one.

All architectures that have THP supported have to provide atomic
pmdp_invalidate(). If generic implementation of pmdp_invalidate() is used,
architecture needs to provide atomic pmdp_mknonpresent().

I've fixed the issue for x86, but I need help with the rest.

So far THP is supported on 8 architectures. Power and S390 already provides
atomic pmdp_invalidate(). x86 is fixed by this patches, so 5 architectures
left:

 - arc;
 - arm;
 - arm64;
 - mips;
 - sparc -- it has custom pmdp_invalidate(), but it's racy too;

Please, help me with them.

Kirill A. Shutemov (3):
  x86/mm: Provide pmdp_mknotpresent() helper
  mm: Do not loose dirty and access bits in pmdp_invalidate()
  mm, thp: Do not loose dirty bit in __split_huge_pmd_locked()

 arch/x86/include/asm/pgtable-3level.h | 17 +++++++++++++++++
 arch/x86/include/asm/pgtable.h        | 13 +++++++++++++
 mm/huge_memory.c                      | 13 +++++++++----
 mm/pgtable-generic.c                  |  3 +--
 4 files changed, 40 insertions(+), 6 deletions(-)

-- 
2.11.0