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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Michal Hocko <mhocko@kernel.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        David Daney <david.daney@cavium.com>,
        David Miller <davem@davemloft.net>,
        "H. Peter Anvin" <hpa@zytor.com>, Hugh Dickins <hughd@google.com>,
        Ingo Molnar <mingo@kernel.org>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Nitin Gupta <nitin.m.gupta@oracle.com>,
        Ralf Baechle <ralf@linux-mips.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vineet Gupta <vgupta@synopsys.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Sasha Levin <alexander.levin@microsoft.com>
Subject: [PATCH 4.4 051/268] asm-generic: provide generic_pmdp_establish()
Date:   Mon, 28 May 2018 12:00:25 +0200
Message-Id: <20180528100207.739905012@linuxfoundation.org>
In-Reply-To: <20180528100202.045206534@linuxfoundation.org>
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4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

[ Upstream commit c58f0bb77ed8bf93dfdde762b01cb67eebbdfc29 ]

Patch series "Do not lose dirty bit on THP pages", v4.

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

The bug can lead to data loss, but the race window is tiny and I haven't
seen any reports that suggested that it happens in reality.  So I don't
think it worth sending it to stable.

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() that returns previous value.

If generic implementation of pmdp_invalidate() is used, architecture
needs to provide atomic pmdp_estabish().

pmdp_estabish() is not used out-side generic implementation of
pmdp_invalidate() so far, but I think this can change in the future.

This patch (of 12):

This is an implementation of pmdp_establish() that is only suitable for
an architecture that doesn't have hardware dirty/accessed bits.  In this
case we can't race with CPU which sets these bits and non-atomic
approach is fine.

Link: http://lkml.kernel.org/r/20171213105756.69879-2-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Daney <david.daney@cavium.com>
Cc: David Miller <davem@davemloft.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Nitin Gupta <nitin.m.gupta@oracle.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 include/asm-generic/pgtable.h |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -237,6 +237,21 @@ extern void pgtable_trans_huge_deposit(s
 extern pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp);
 #endif
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+/*
+ * This is an implementation of pmdp_establish() that is only suitable for an
+ * architecture that doesn't have hardware dirty/accessed bits. In this case we
+ * can't race with CPU which sets these bits and non-atomic aproach is fine.
+ */
+static inline pmd_t generic_pmdp_establish(struct vm_area_struct *vma,
+		unsigned long address, pmd_t *pmdp, pmd_t pmd)
+{
+	pmd_t old_pmd = *pmdp;
+	set_pmd_at(vma->vm_mm, address, pmdp, pmd);
+	return old_pmd;
+}
+#endif
+
 #ifndef __HAVE_ARCH_PMDP_INVALIDATE
 extern void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
 			    pmd_t *pmdp);