[PATCH] mm: pagewalk: call pte_hole() for VM_PFNMAP during walk_page_range

[PATCH] mm: pagewalk: call pte_hole() for VM_PFNMAP during walk_page_range

[Shiraz Hashim]

walk_page_range silently skips vma having VM_PFNMAP set,
which leads to undesirable behaviour at client end (who
called walk_page_range). For example for pagemap_read,
when no callbacks are called against VM_PFNMAP vma,
pagemap_read may prepare pagemap data for next virtual
address range at wrong index.

Signed-off-by: Shiraz Hashim <shashim@codeaurora.org>
---
The fix is revised, based upon the suggestion here at
http://www.spinics.net/lists/linux-mm/msg83058.html

 mm/pagewalk.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index ad83195..b264bda 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -199,7 +199,10 @@ int walk_page_range(unsigned long addr, unsigned long end,
 			 */
 			if ((vma->vm_start <= addr) &&
 			    (vma->vm_flags & VM_PFNMAP)) {
-				next = vma->vm_end;
+				if (walk->pte_hole)
+					err = walk->pte_hole(addr, next, walk);
+				if (err)
+					break;
 				pgd = pgd_offset(walk->mm, next);
 				continue;
 			}
-- 
Shiraz Hashim

QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
member of the Code Aurora Forum, hosted by The Linux Foundation

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Re: [PATCH] mm: pagewalk: call pte_hole() for VM_PFNMAP during walk_page_range

[Naoya Horiguchi]

On Wed, Jan 21, 2015 at 11:43:13AM +0530, Shiraz Hashim wrote:
> walk_page_range silently skips vma having VM_PFNMAP set,
> which leads to undesirable behaviour at client end (who
> called walk_page_range). For example for pagemap_read,
> when no callbacks are called against VM_PFNMAP vma,
> pagemap_read may prepare pagemap data for next virtual
> address range at wrong index.
> 
> Signed-off-by: Shiraz Hashim <shashim@codeaurora.org>

Thank you!

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

> ---
> The fix is revised, based upon the suggestion here at
> http://www.spinics.net/lists/linux-mm/msg83058.html
> 
>  mm/pagewalk.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/pagewalk.c b/mm/pagewalk.c
> index ad83195..b264bda 100644
> --- a/mm/pagewalk.c
> +++ b/mm/pagewalk.c
> @@ -199,7 +199,10 @@ int walk_page_range(unsigned long addr, unsigned long end,
>  			 */
>  			if ((vma->vm_start <= addr) &&
>  			    (vma->vm_flags & VM_PFNMAP)) {
> -				next = vma->vm_end;
> +				if (walk->pte_hole)
> +					err = walk->pte_hole(addr, next, walk);
> +				if (err)
> +					break;
>  				pgd = pgd_offset(walk->mm, next);
>  				continue;
>  			}
> -- 
> Shiraz Hashim
> 
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
> member of the Code Aurora Forum, hosted by The Linux Foundation
> 
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> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
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Re: [PATCH] mm: pagewalk: call pte_hole() for VM_PFNMAP during walk_page_range

[Andrew Morton]

On Wed, 21 Jan 2015 11:43:13 +0530 Shiraz Hashim <shashim@codeaurora.org> wrote:

> walk_page_range silently skips vma having VM_PFNMAP set,
> which leads to undesirable behaviour at client end (who
> called walk_page_range). For example for pagemap_read,
> when no callbacks are called against VM_PFNMAP vma,
> pagemap_read may prepare pagemap data for next virtual
> address range at wrong index.

This changelog doesn't have enough information for me to be able to
work out whether a -stable backport is needed.  Please always describe
the user-visible effects of a bug.

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