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SubjectRe: [PATCH v3] mm/pagewalk.c: walk_page_range should avoid VM_PFNMAP areas
On Wed, May 15, 2013 at 07:46:36AM -0500, Cliff Wickman wrote:
>
> /proc/<pid>/smaps and similar walks through a user page table should not
> be looking at VM_PFNMAP areas.
>
> v2:
> - moves the VM_BUG_ON out of the loop
> - adds the needed test for vma->vm_start <= addr
>
> v3 adds comments to make this clearer, as N. Horiguchi recommends:
> > I recommend that you check VM_PFNMAP in the possible callers' side.
> > But this patch seems to solve your problem, so with properly commenting
> > this somewhere, I do not oppose it.
>
> Certain tests in walk_page_range() (specifically split_huge_page_pmd())
> assume that all 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.
>
> There are a half dozen callers of walk_page_range() that walk through
> a task's entire page table (as N. Horiguchi pointed out). So rather than
> change all of them, this patch changes just walk_page_range() to ignore
> VM_PFNMAP areas.
>
> The logic of hugetlb_vma() is moved back into walk_page_range(), as we
> want to test any vma in the range.
>
> 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
> - and probably several out-of-tree modules
>
> I'm copying everyone who has changed this file recently, in case
> there is some reason that I am not aware of to provide
> /proc/<pid>/smaps|clear_refs|maps|numa_maps for these VM_PFNMAP areas.
>
> Signed-off-by: Cliff Wickman <cpw@sgi.com>

Thank you.

Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>


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