[PATCH v2] thp: use is_zero_pfn only after pte_present check

[PATCH v2] thp: use is_zero_pfn only after pte_present check

[Minchan Kim]

Use is_zero_pfn on pteval only after pte_present check on pteval
(It might be better idea to introduce is_zero_pte where checks
pte_present first). Otherwise, it could work with swap or
migration entry and if pte_pfn's result is equal to zero_pfn
by chance, we lose user's data in __collapse_huge_page_copy.
So if you're luck, the application is segfaulted and finally you
could see below message when the application is exit.

BUG: Bad rss-counter state mm:ffff88007f099300 idx:2 val:3

Cc: <stable@vger.kernel.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
Hello Greg,

This patch should go to -stable but when you will apply it
after merging of linus tree, it will be surely conflicted due
to userfaultfd part.

I want to know how to handle it.

Thanks.

 mm/huge_memory.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 4b06b8db9df2..bbac913f96bc 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2206,7 +2206,8 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 	for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
 	     _pte++, address += PAGE_SIZE) {
 		pte_t pteval = *_pte;
-		if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
+		if (pte_none(pteval) || (pte_present(pteval) &&
+				is_zero_pfn(pte_pfn(pteval)))) {
 			if (!userfaultfd_armed(vma) &&
 			    ++none_or_zero <= khugepaged_max_ptes_none)
 				continue;
-- 
1.9.1

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Re: [PATCH v2] thp: use is_zero_pfn only after pte_present check

[Greg Kroah-Hartman]

On Tue, Oct 13, 2015 at 11:38:38AM +0900, Minchan Kim wrote:
> Use is_zero_pfn on pteval only after pte_present check on pteval
> (It might be better idea to introduce is_zero_pte where checks
> pte_present first). Otherwise, it could work with swap or
> migration entry and if pte_pfn's result is equal to zero_pfn
> by chance, we lose user's data in __collapse_huge_page_copy.
> So if you're luck, the application is segfaulted and finally you
> could see below message when the application is exit.
> 
> BUG: Bad rss-counter state mm:ffff88007f099300 idx:2 val:3
> 
> Cc: <stable@vger.kernel.org>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
> Hello Greg,
> 
> This patch should go to -stable but when you will apply it
> after merging of linus tree, it will be surely conflicted due
> to userfaultfd part.
> 
> I want to know how to handle it.

You will get an automated email saying it didn't apply and then you
provide a backported version.  Or you send a properly backported version
to stable@vger.kernel.org before then, with the git commit id of the
patch in Linus's tree.

thanks,

greg k-h

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Re: [PATCH v2] thp: use is_zero_pfn only after pte_present check

[Minchan Kim]

On Mon, Oct 12, 2015 at 10:41:24PM -0700, Greg Kroah-Hartman wrote:
> On Tue, Oct 13, 2015 at 11:38:38AM +0900, Minchan Kim wrote:
> > Use is_zero_pfn on pteval only after pte_present check on pteval
> > (It might be better idea to introduce is_zero_pte where checks
> > pte_present first). Otherwise, it could work with swap or
> > migration entry and if pte_pfn's result is equal to zero_pfn
> > by chance, we lose user's data in __collapse_huge_page_copy.
> > So if you're luck, the application is segfaulted and finally you
> > could see below message when the application is exit.
> > 
> > BUG: Bad rss-counter state mm:ffff88007f099300 idx:2 val:3
> > 
> > Cc: <stable@vger.kernel.org>
> > Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > ---
> > Hello Greg,
> > 
> > This patch should go to -stable but when you will apply it
> > after merging of linus tree, it will be surely conflicted due
> > to userfaultfd part.
> > 
> > I want to know how to handle it.
> 
> You will get an automated email saying it didn't apply and then you
> provide a backported version.  Or you send a properly backported version
> to stable@vger.kernel.org before then, with the git commit id of the
> patch in Linus's tree.

Okay, I will send a right version when I received automatd email.
Thanks.

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Re: [PATCH v2] thp: use is_zero_pfn only after pte_present check

[Vlastimil Babka]

On 10/13/2015 04:38 AM, Minchan Kim wrote:
> Use is_zero_pfn on pteval only after pte_present check on pteval
> (It might be better idea to introduce is_zero_pte where checks
> pte_present first). Otherwise, it could work with swap or
> migration entry and if pte_pfn's result is equal to zero_pfn
> by chance, we lose user's data in __collapse_huge_page_copy.
> So if you're luck, the application is segfaulted and finally you
> could see below message when the application is exit.
>
> BUG: Bad rss-counter state mm:ffff88007f099300 idx:2 val:3
>
> Cc: <stable@vger.kernel.org>

More specific:
Cc: <stable@vger.kernel.org> # 4.1+
Fixes: ca0984caa823 ("mm: incorporate zero pages into transparent huge 
pages")

> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
> Hello Greg,
>
> This patch should go to -stable but when you will apply it
> after merging of linus tree, it will be surely conflicted due
> to userfaultfd part.
>
> I want to know how to handle it.
>
> Thanks.
>
>   mm/huge_memory.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 4b06b8db9df2..bbac913f96bc 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2206,7 +2206,8 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
>   	for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
>   	     _pte++, address += PAGE_SIZE) {
>   		pte_t pteval = *_pte;
> -		if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
> +		if (pte_none(pteval) || (pte_present(pteval) &&
> +				is_zero_pfn(pte_pfn(pteval)))) {
>   			if (!userfaultfd_armed(vma) &&
>   			    ++none_or_zero <= khugepaged_max_ptes_none)
>   				continue;
>

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Re: [PATCH v2] thp: use is_zero_pfn only after pte_present check

[Minchan Kim]

On Tue, Oct 13, 2015 at 09:28:23AM +0200, Vlastimil Babka wrote:
> On 10/13/2015 04:38 AM, Minchan Kim wrote:
> >Use is_zero_pfn on pteval only after pte_present check on pteval
> >(It might be better idea to introduce is_zero_pte where checks
> >pte_present first). Otherwise, it could work with swap or
> >migration entry and if pte_pfn's result is equal to zero_pfn
> >by chance, we lose user's data in __collapse_huge_page_copy.
> >So if you're luck, the application is segfaulted and finally you
> >could see below message when the application is exit.
> >
> >BUG: Bad rss-counter state mm:ffff88007f099300 idx:2 val:3
> >
> >Cc: <stable@vger.kernel.org>
> 
> More specific:
> Cc: <stable@vger.kernel.org> # 4.1+
> Fixes: ca0984caa823 ("mm: incorporate zero pages into transparent
> huge pages")
> 
> >Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> 
> Acked-by: Vlastimil Babka <vbabka@suse.cz>

Thanks for the detail and review, Vlastimil.

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