diff mbox series

[v4,03/10] mm/gup: fail get_user_pages for LONGTERM dev coherent type

Message ID 20220127030949.19396-4-alex.sierra@amd.com (mailing list archive)
State New
Headers show
Series Add MEMORY_DEVICE_COHERENT for coherent device memory mapping | expand

Commit Message

Sierra Guiza, Alejandro (Alex) Jan. 27, 2022, 3:09 a.m. UTC
Avoid long term pinning for Coherent device type pages. This could
interfere with their own device memory manager. For now, we are just
returning error for PIN_LONGTERM Coherent device type pages. Eventually,
these type of pages will get migrated to system memory, once the device
migration pages support is added.

Signed-off-by: Alex Sierra <alex.sierra@amd.com>
---
 mm/gup.c | 7 +++++++
 1 file changed, 7 insertions(+)

Comments

Alistair Popple Jan. 28, 2022, 2:36 a.m. UTC | #1
On Thursday, 27 January 2022 2:09:42 PM AEDT Alex Sierra wrote:
> Avoid long term pinning for Coherent device type pages. This could
> interfere with their own device memory manager. For now, we are just
> returning error for PIN_LONGTERM Coherent device type pages. Eventually,
> these type of pages will get migrated to system memory, once the device
> migration pages support is added.
> 
> Signed-off-by: Alex Sierra <alex.sierra@amd.com>
> ---
>  mm/gup.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 886d6148d3d0..5291d7221826 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1720,6 +1720,12 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
>  		 * If we get a movable page, since we are going to be pinning
>  		 * these entries, try to move them out if possible.
>  		 */
> +		if (is_dev_private_or_coherent_page(head)) {
> +			WARN_ON_ONCE(is_device_private_page(head));
> +			ret = -EFAULT;
> +			goto unpin_pages;
> +		}
> +
>  		if (!is_pinnable_page(head)) {
>  			if (PageHuge(head)) {
>  				if (!isolate_huge_page(head, &movable_page_list))
> @@ -1750,6 +1756,7 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
>  	if (list_empty(&movable_page_list) && !isolation_error_count)
>  		return nr_pages;
>  
> +unpin_pages:
>  	if (gup_flags & FOLL_PIN) {
>  		unpin_user_pages(pages, nr_pages);
>  	} else {
 
If there is a mix of ZONE_MOVABLE and device pages the return value (ret) will
be subsequently lost here:

        if (!list_empty(&movable_page_list)) {
                ret = migrate_pages(&movable_page_list, alloc_migration_target,
                                    NULL, (unsigned long)&mtc, MIGRATE_SYNC,
                                    MR_LONGTERM_PIN, NULL);
                if (ret && !list_empty(&movable_page_list))
                        putback_movable_pages(&movable_page_list);
        }

Which won't actually cause any problems, but it will lead to the GUP getting
retried unnecessarily. I do still intend to address this with a series to
migrate pages instead though, so I think this is ok for now as it's an unlikely
corner case anyway. Therefore feel tree to add the below when you repost:

Reviewed-by: Alistair Poppple <apopple@nvidia.com>
diff mbox series

Patch

diff --git a/mm/gup.c b/mm/gup.c
index 886d6148d3d0..5291d7221826 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1720,6 +1720,12 @@  static long check_and_migrate_movable_pages(unsigned long nr_pages,
 		 * If we get a movable page, since we are going to be pinning
 		 * these entries, try to move them out if possible.
 		 */
+		if (is_dev_private_or_coherent_page(head)) {
+			WARN_ON_ONCE(is_device_private_page(head));
+			ret = -EFAULT;
+			goto unpin_pages;
+		}
+
 		if (!is_pinnable_page(head)) {
 			if (PageHuge(head)) {
 				if (!isolate_huge_page(head, &movable_page_list))
@@ -1750,6 +1756,7 @@  static long check_and_migrate_movable_pages(unsigned long nr_pages,
 	if (list_empty(&movable_page_list) && !isolation_error_count)
 		return nr_pages;
 
+unpin_pages:
 	if (gup_flags & FOLL_PIN) {
 		unpin_user_pages(pages, nr_pages);
 	} else {