Nouveau - Jan 2025 - [PATCH v1 07/12] mm/page_vma_mapped: device-private entries are not migration entries

It's unclear why they would be considered migration entries; they are
not.

Likely we'll never really trigger that case in practice, because
migration (including folio split) of a folio that has device-private
entries is never started, as we would detect "additional references":
device-private entries adjust the mapcount, but not the refcount.

Fixes: b756a3b5e7ea ("mm: device exclusive memory access")
Signed-off-by: David Hildenbrand <david at redhat.com>
---
 mm/page_vma_mapped.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 81839a9e74f1..32679be22d30 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -111,8 +111,7 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw)
 			return false;
 		entry = pte_to_swp_entry(ptent);
 
-		if (!is_migration_entry(entry) &&
-		    !is_device_exclusive_entry(entry))
+		if (!is_migration_entry(entry))
 			return false;
 
 		pfn = swp_offset_pfn(entry);
-- 
2.48.1

On Wed, Jan 29, 2025 at 12:54:05PM +0100, David Hildenbrand
wrote:
> It's unclear why they would be considered migration entries; they are
> not.
Yeah, I agree that doesn't seem right. I suspect I was initially modelling
device exclusive entries similar to migration entries but obviously went too
far. So thanks for fixing:

Reviewed-by: Alistair Popple <apopple at nvidia.com>
> Likely we'll never really trigger that case in practice, because
> migration (including folio split) of a folio that has device-private
> entries is never started, as we would detect "additional
references":
> device-private entries adjust the mapcount, but not the refcount.
> 
> Fixes: b756a3b5e7ea ("mm: device exclusive memory access")
> Signed-off-by: David Hildenbrand <david at redhat.com>
> ---
>  mm/page_vma_mapped.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
> index 81839a9e74f1..32679be22d30 100644
> --- a/mm/page_vma_mapped.c
> +++ b/mm/page_vma_mapped.c
> @@ -111,8 +111,7 @@ static bool check_pte(struct page_vma_mapped_walk
*pvmw)
>  			return false;
>  		entry = pte_to_swp_entry(ptent);
>  
> -		if (!is_migration_entry(entry) &&
> -		    !is_device_exclusive_entry(entry))
> +		if (!is_migration_entry(entry))
>  			return false;
>  
>  		pfn = swp_offset_pfn(entry);
> -- 
> 2.48.1
>