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Subject[PATCH] VM, x86, PAT: Change implementation of is_linear_pfn_mapping

Use of vma->vm_pgoff to identify the pfnmaps that are fully
mapped at mmap time is broke. vm_pgoff is set by generic mmap
code even for cases where drivers are setting up the mappings
at the fault time.

The problem was originally reported here.
http://marc.info/?l=linux-kernel&m=123383810628583&w=2

Change is_linear_pfn_mapping logic to overload VM_NONLINEAR
flag along with VM_PFNMAP to mean full PFNMAP setup at mmap
time.

Acked-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha>@intel.com>
---
arch/x86/mm/pat.c | 5 +++--
include/linux/mm.h | 8 +++++++-
mm/memory.c | 6 ++++--
3 files changed, 14 insertions(+), 5 deletions(-)
diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 2ed3715..640339e 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -677,10 +677,11 @@ static int reserve_pfn_range(u64 paddr, unsigned long size, pgprot_t *vma_prot,
is_ram = pat_pagerange_is_ram(paddr, paddr + size);

/*
- * reserve_pfn_range() doesn't support RAM pages.
+ * reserve_pfn_range() doesn't support RAM pages. Maintain the current
+ * behavior with RAM pages by returning success.
*/
if (is_ram != 0)
- return -EINVAL;
+ return 0;

ret = reserve_memtype(paddr, paddr + size, want_flags, &flags);
if (ret)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 065cdf8..6c3fc3a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -127,6 +127,12 @@ extern unsigned int kobjsize(const void *objp);
#define VM_SPECIAL (VM_IO | VM_DONTEXPAND | VM_RESERVED | VM_PFNMAP)

/*
+ * pfnmap vmas that are fully mapped at mmap time (not mapped on fault).
+ * Used by x86 PAT to identify such PFNMAP mappings and optimize their handling.
+ */
+#define VM_PFNMAP_AT_MMAP (VM_NONLINEAR | VM_PFNMAP)
+
+/*
* mapping from the currently active vm_flags protection bits (the
* low four bits) to a page protection mask..
*/
@@ -145,7 +151,7 @@ extern pgprot_t protection_map[16];
*/
static inline int is_linear_pfn_mapping(struct vm_area_struct *vma)
{
- return ((vma->vm_flags & VM_PFNMAP) && vma->vm_pgoff);
+ return ((vma->vm_flags & VM_PFNMAP_AT_MMAP) == VM_PFNMAP_AT_MMAP);
}

static inline int is_pfn_mapping(struct vm_area_struct *vma)
diff --git a/mm/memory.c b/mm/memory.c
index 05fab3b..e6aced9 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1675,9 +1675,10 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
* behaviour that some programs depend on. We mark the "original"
* un-COW'ed pages by matching them up with "vma->vm_pgoff".
*/
- if (addr == vma->vm_start && end == vma->vm_end)
+ if (addr == vma->vm_start && end == vma->vm_end) {
vma->vm_pgoff = pfn;
- else if (is_cow_mapping(vma->vm_flags))
+ vma->vm_flags |= VM_PFNMAP_AT_MMAP;
+ } else if (is_cow_mapping(vma->vm_flags))
return -EINVAL;

vma->vm_flags |= VM_IO | VM_RESERVED | VM_PFNMAP;
@@ -1689,6 +1690,7 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
* needed from higher level routine calling unmap_vmas
*/
vma->vm_flags &= ~(VM_IO | VM_RESERVED | VM_PFNMAP);
+ vma->vm_flags &= ~VM_PFNMAP_AT_MMAP;
return -EINVAL;
}

--
1.6.0.6


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