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Subject[tip:x86/mm] x86/mm/pat: Add untrack_pfn_moved for mremap
Commit-ID:  d9fe4fab11976e56b2e992980bf6ce948bdf02ac
Gitweb: http://git.kernel.org/tip/d9fe4fab11976e56b2e992980bf6ce948bdf02ac
Author: Toshi Kani <toshi.kani@hpe.com>
AuthorDate: Tue, 22 Dec 2015 17:54:23 -0700
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Tue, 5 Jan 2016 11:10:05 +0100

x86/mm/pat: Add untrack_pfn_moved for mremap

mremap() with MREMAP_FIXED on a VM_PFNMAP range causes the following
WARN_ON_ONCE() message in untrack_pfn().

WARNING: CPU: 1 PID: 3493 at arch/x86/mm/pat.c:985 untrack_pfn+0xbd/0xd0()
Call Trace:
[<ffffffff817729ea>] dump_stack+0x45/0x57
[<ffffffff8109e4b6>] warn_slowpath_common+0x86/0xc0
[<ffffffff8109e5ea>] warn_slowpath_null+0x1a/0x20
[<ffffffff8106a88d>] untrack_pfn+0xbd/0xd0
[<ffffffff811d2d5e>] unmap_single_vma+0x80e/0x860
[<ffffffff811d3725>] unmap_vmas+0x55/0xb0
[<ffffffff811d916c>] unmap_region+0xac/0x120
[<ffffffff811db86a>] do_munmap+0x28a/0x460
[<ffffffff811dec33>] move_vma+0x1b3/0x2e0
[<ffffffff811df113>] SyS_mremap+0x3b3/0x510
[<ffffffff817793ee>] entry_SYSCALL_64_fastpath+0x12/0x71

MREMAP_FIXED moves a pfnmap from old vma to new vma. untrack_pfn() is
called with the old vma after its pfnmap page table has been removed,
which causes follow_phys() to fail. The new vma has a new pfnmap to
the same pfn & cache type with VM_PAT set. Therefore, we only need to
clear VM_PAT from the old vma in this case.

Add untrack_pfn_moved(), which clears VM_PAT from a given old vma.
move_vma() is changed to call this function with the old vma when
VM_PFNMAP is set. move_vma() then calls do_munmap(), and untrack_pfn()
is a no-op since VM_PAT is cleared.

Reported-by: Stas Sergeev <stsp@list.ru>
Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/1450832064-10093-2-git-send-email-toshi.kani@hpe.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/mm/pat.c | 10 ++++++++++
include/asm-generic/pgtable.h | 10 +++++++++-
mm/mremap.c | 4 ++++
3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 188e3e0..1aca073 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -992,6 +992,16 @@ void untrack_pfn(struct vm_area_struct *vma, unsigned long pfn,
vma->vm_flags &= ~VM_PAT;
}

+/*
+ * untrack_pfn_moved is called, while mremapping a pfnmap for a new region,
+ * with the old vma after its pfnmap page table has been removed. The new
+ * vma has a new pfnmap to the same pfn & cache type with VM_PAT set.
+ */
+void untrack_pfn_moved(struct vm_area_struct *vma)
+{
+ vma->vm_flags &= ~VM_PAT;
+}
+
pgprot_t pgprot_writecombine(pgprot_t prot)
{
return __pgprot(pgprot_val(prot) |
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 14b0ff32..3a6803c 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -569,7 +569,7 @@ static inline int track_pfn_copy(struct vm_area_struct *vma)
}

/*
- * untrack_pfn_vma is called while unmapping a pfnmap for a region.
+ * untrack_pfn is called while unmapping a pfnmap for a region.
* untrack can be called for a specific region indicated by pfn and size or
* can be for the entire vma (in which case pfn, size are zero).
*/
@@ -577,6 +577,13 @@ static inline void untrack_pfn(struct vm_area_struct *vma,
unsigned long pfn, unsigned long size)
{
}
+
+/*
+ * untrack_pfn_moved is called while mremapping a pfnmap for a new region.
+ */
+static inline void untrack_pfn_moved(struct vm_area_struct *vma)
+{
+}
#else
extern int track_pfn_remap(struct vm_area_struct *vma, pgprot_t *prot,
unsigned long pfn, unsigned long addr,
@@ -586,6 +593,7 @@ extern int track_pfn_insert(struct vm_area_struct *vma, pgprot_t *prot,
extern int track_pfn_copy(struct vm_area_struct *vma);
extern void untrack_pfn(struct vm_area_struct *vma, unsigned long pfn,
unsigned long size);
+extern void untrack_pfn_moved(struct vm_area_struct *vma);
#endif

#ifdef __HAVE_COLOR_ZERO_PAGE
diff --git a/mm/mremap.c b/mm/mremap.c
index c25bc62..de824e7 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -319,6 +319,10 @@ static unsigned long move_vma(struct vm_area_struct *vma,
hiwater_vm = mm->hiwater_vm;
vm_stat_account(mm, vma->vm_flags, vma->vm_file, new_len>>PAGE_SHIFT);

+ /* Tell pfnmap has moved from this vma */
+ if (unlikely(vma->vm_flags & VM_PFNMAP))
+ untrack_pfn_moved(vma);
+
if (do_munmap(mm, old_addr, old_len) < 0) {
/* OOM: unable to split vma, just get accounts right */
vm_unacct_memory(excess >> PAGE_SHIFT);

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