[PATCH v1 04/15] mm: add device coherent checker to remove migration pte

[Sierra Guiza, Alejandro (Alex)]

@apopple at nvidia.com Could you please check this patch? It's somehow related to migrate_device_page() for long term device coherent pages.

Regards,
Alex Sierra
> -----Original Message-----
> From: amd-gfx <amd-gfx-bounces at lists.freedesktop.org> On Behalf Of Alex
> Sierra
> Sent: Thursday, May 5, 2022 4:34 PM
> To: jgg at nvidia.com
> Cc: rcampbell at nvidia.com; willy at infradead.org; david at redhat.com;
> Kuehling, Felix <Felix.Kuehling at amd.com>; apopple at nvidia.com; amd-
> gfx at lists.freedesktop.org; linux-xfs at vger.kernel.org; linux-mm at kvack.org;
> jglisse at redhat.com; dri-devel at lists.freedesktop.org; akpm at linux-
> foundation.org; linux-ext4 at vger.kernel.org; hch at lst.de
> Subject: [PATCH v1 04/15] mm: add device coherent checker to remove
> migration pte
> 
> During remove_migration_pte(), entries for device coherent type pages that
> were not created through special migration ptes, ignore _PAGE_RW flag. This
> path can be found at migrate_device_page(), where valid vma is not
> required. In this case, migrate_vma_collect_pmd() is not called and special
> migration ptes are not set.
> 
> Signed-off-by: Alex Sierra <alex.sierra at amd.com>
> ---
>  mm/migrate.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c index
> 6c31ee1e1c9b..e18ddee56f37 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -206,7 +206,8 @@ static bool remove_migration_pte(struct folio *folio,
>  		 * Recheck VMA as permissions can change since migration
> started
>  		 */
>  		entry = pte_to_swp_entry(*pvmw.pte);
> -		if (is_writable_migration_entry(entry))
> +		if (is_writable_migration_entry(entry) ||
> +		    is_device_coherent_page(pfn_to_page(pvmw.pfn)))
>  			pte = maybe_mkwrite(pte, vma);
>  		else if (pte_swp_uffd_wp(*pvmw.pte))
>  			pte = pte_mkuffd_wp(pte);
> --
> 2.32.0