@[email protected] 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 <[email protected]> On Behalf Of Alex
> Sierra
> Sent: Thursday, May 5, 2022 4:34 PM
> To: [email protected]
> Cc: [email protected]; [email protected]; [email protected];
> Kuehling, Felix <[email protected]>; [email protected]; amd-
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; akpm@linux-
> foundation.org; [email protected]; [email protected]
> 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 <[email protected]>
> ---
> 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
"Sierra Guiza, Alejandro (Alex)" <[email protected]> writes:
> @[email protected] 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 <[email protected]> On Behalf Of Alex
>> Sierra
>> Sent: Thursday, May 5, 2022 4:34 PM
>> To: [email protected]
>> Cc: [email protected]; [email protected]; [email protected];
>> Kuehling, Felix <[email protected]>; [email protected]; amd-
>> [email protected]; [email protected]; [email protected];
>> [email protected]; [email protected]; akpm@linux-
>> foundation.org; [email protected]; [email protected]
>> 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.
It's true that we don't call migrate_vma_collect_pmd() for
migrate_device_page(), but this doesn't imply migration entries are not
created. We still call migrate_vma_unmap() which calls try_to_migrate()
to install migration entries.
When we have a vma migrate_vma_collect_pmd() is a fast path for the
common case a page is only mapped once. So migrate_vma_collect_pmd()
should fairly closely match try_to_migrate_one(). I did experiment
locally with removing the fast path to simplify the code, but it does
provide a meaningful performance improvement so I abandoned it.
I think you're running into the problem addressed by
https://lkml.kernel.org/r/[email protected]
but for DEVICE_COHERENT pages.
Based on that I think the approach below is wrong. You should update
try_to_migrate_one() to deal with DEVICE_COHERENT pages. It would make
sense to do that as part of patch 1 in this series.
The problem is that try_to_migrate_one() assumes folio_is_zone_device()
implies it is a DEVICE_PRIVATE page due to the check in
try_to_migrate().
>> Signed-off-by: Alex Sierra <[email protected]>
>> ---
>> 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