[PATCH] mm: teach mincore_hugetlb about pte markers

[PATCH] mm: teach mincore_hugetlb about pte markers

[James Houghton]

By checking huge_pte_none(), we incorrectly classify PTE markers as
"present". Instead, check huge_pte_none_mostly(), classifying PTE
markers the same as if the PTE were completely blank.

PTE markers, unlike other kinds of swap entries, don't reference any
physical page and don't indicate that a physical page was mapped
previously. As such, treat them as non-present for the sake of
mincore().

Fixes: 5c041f5d1f23 ("mm: teach core mm about pte markers")
Signed-off-by: James Houghton <jthoughton@google.com>
---
 mm/mincore.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/mincore.c b/mm/mincore.c
index cd69b9db0081..d359650b0f75 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -33,7 +33,7 @@ static int mincore_hugetlb(pte_t *pte, unsigned long hmask, unsigned long addr,
 	 * Hugepages under user process are always in RAM and never
 	 * swapped out, but theoretically it needs to be checked.
 	 */
-	present = pte && !huge_pte_none(huge_ptep_get(pte));
+	present = pte && !huge_pte_none_mostly(huge_ptep_get(pte));
 	for (; addr != end; vec++, addr += PAGE_SIZE)
 		*vec = present;
 	walk->private = vec;
-- 
2.40.0.rc0.216.gc4246ad0f0-goog

Re: [PATCH] mm: teach mincore_hugetlb about pte markers

[Peter Xu]

On Thu, Mar 02, 2023 at 10:24:04PM +0000, James Houghton wrote:
> By checking huge_pte_none(), we incorrectly classify PTE markers as
> "present". Instead, check huge_pte_none_mostly(), classifying PTE
> markers the same as if the PTE were completely blank.
> 
> PTE markers, unlike other kinds of swap entries, don't reference any
> physical page and don't indicate that a physical page was mapped
> previously. As such, treat them as non-present for the sake of
> mincore().
> 
> Fixes: 5c041f5d1f23 ("mm: teach core mm about pte markers")
> Signed-off-by: James Houghton <jthoughton@google.com>

Acked-by: Peter Xu <peterx@redhat.com>

Thanks, James.

-- 
Peter Xu

Re: [PATCH] mm: teach mincore_hugetlb about pte markers

[Andrew Morton]

On Thu, 2 Mar 2023 17:32:48 -0500 Peter Xu <peterx@redhat.com> wrote:

> On Thu, Mar 02, 2023 at 10:24:04PM +0000, James Houghton wrote:
> > By checking huge_pte_none(), we incorrectly classify PTE markers as
> > "present". Instead, check huge_pte_none_mostly(), classifying PTE
> > markers the same as if the PTE were completely blank.
> > 
> > PTE markers, unlike other kinds of swap entries, don't reference any
> > physical page and don't indicate that a physical page was mapped
> > previously. As such, treat them as non-present for the sake of
> > mincore().
> > 
> > Fixes: 5c041f5d1f23 ("mm: teach core mm about pte markers")
> > Signed-off-by: James Houghton <jthoughton@google.com>
> 
> Acked-by: Peter Xu <peterx@redhat.com>
> 

I think I'll add cc:stable to this. 

Re: [PATCH] mm: teach mincore_hugetlb about pte markers

[David Hildenbrand]

On 02.03.23 23:24, James Houghton wrote:
> By checking huge_pte_none(), we incorrectly classify PTE markers as
> "present". Instead, check huge_pte_none_mostly(), classifying PTE
> markers the same as if the PTE were completely blank.
> 
> PTE markers, unlike other kinds of swap entries, don't reference any
> physical page and don't indicate that a physical page was mapped
> previously. As such, treat them as non-present for the sake of
> mincore().
> 
> Fixes: 5c041f5d1f23 ("mm: teach core mm about pte markers")
> Signed-off-by: James Houghton <jthoughton@google.com>
> ---
>   mm/mincore.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/mincore.c b/mm/mincore.c
> index cd69b9db0081..d359650b0f75 100644
> --- a/mm/mincore.c
> +++ b/mm/mincore.c
> @@ -33,7 +33,7 @@ static int mincore_hugetlb(pte_t *pte, unsigned long hmask, unsigned long addr,
>   	 * Hugepages under user process are always in RAM and never
>   	 * swapped out, but theoretically it needs to be checked.
>   	 */
> -	present = pte && !huge_pte_none(huge_ptep_get(pte));
> +	present = pte && !huge_pte_none_mostly(huge_ptep_get(pte));
>   	for (; addr != end; vec++, addr += PAGE_SIZE)
>   		*vec = present;
>   	walk->private = vec;

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb