[PATCH] fs/proc: smaps should avoid VM_PFNMAP areas

From: Cliff Wickman
Date: Mon Apr 29 2013 - 17:26:02 EST

/proc/<pid>/smaps should not be looking at VM_PFNMAP areas.

Certain tests in show_smap() (especially for huge pages) assume that the
mapped PFN's are backed with page structures. And this is not usually true
for VM_PFNMAP areas. This can result in panics on kernel page faults when
attempting to address those page structures.

VM_PFNMAP areas are used by
- graphics memory manager gpu/drm/drm_gem.c
- global reference unit sgi-gru/grufile.c
- sgi special memory char/mspec.c
- probably several out-of-tree modules

I'm copying everyone who has changed fs/proc/task_mmu.c recently, in case
of some reason to provide /proc/<pid>/smaps for these areas that I am not
aware of.

Signed-off-by: Cliff Wickman <cpw@xxxxxxx>
fs/proc/task_mmu.c | 3 +++
1 file changed, 3 insertions(+)

Index: linux/fs/proc/task_mmu.c
--- linux.orig/fs/proc/task_mmu.c
+++ linux/fs/proc/task_mmu.c
@@ -589,6 +589,9 @@ static int show_smap(struct seq_file *m,
.private = &mss,

+ if (vma->vm_flags & VM_PFNMAP)
+ return 0;
memset(&mss, 0, sizeof mss);
mss.vma = vma;
/* mmap_sem is held in m_start */
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