diff mbox series

[v3,03/10] mm/gup: fail get_user_pages for LONGTERM dev coherent type

Message ID 20220110223201.31024-4-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. 10, 2022, 10:31 p.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

Joao Martins Jan. 20, 2022, 12:36 p.m. UTC | #1
On 1/10/22 22:31, 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..9c8a075d862d 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_device_page(head)) {
> +			WARN_ON_ONCE(is_device_private_page(head));
> +			ret = -EFAULT;
> +			goto unpin_pages;
> +		}
> +

Wouldn't be more efficient for you failing earlier instead of after all the pages are pinned?

Filesystem DAX suffers from a somewhat similar issue[0] -- albeit it's more related to
blocking FOLL_LONGTERM in gup-fast while gup-slow can still do it. Coherent devmap appears
to want to block it in all gup.

On another thread Jason was suggesting about having different pgmap::flags to capture
these special cases[1] instead of selecting what different pgmap types can do in various
different places.

[0] https://lore.kernel.org/linux-mm/6a18179e-65f7-367d-89a9-d5162f10fef0@oracle.com/
[1] https://lore.kernel.org/linux-mm/20211019160136.GH3686969@ziepe.ca/
Alistair Popple Jan. 20, 2022, 1:18 p.m. UTC | #2
On Thursday, 20 January 2022 11:36:21 PM AEDT Joao Martins wrote:
> On 1/10/22 22:31, 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..9c8a075d862d 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_device_page(head)) {
> > +			WARN_ON_ONCE(is_device_private_page(head));
> > +			ret = -EFAULT;
> > +			goto unpin_pages;
> > +		}
> > +
> 
> Wouldn't be more efficient for you failing earlier instead of after all the pages are pinned?

Rather than failing I think the plan is to migrate the device coherent pages
like we do for ZONE_MOVABLE, so leaving this here is a good place holder until
that is done. Currently we are missing some functionality required to do that
but I am hoping to post a series fixing that soon.

> Filesystem DAX suffers from a somewhat similar issue[0] -- albeit it's more related to
> blocking FOLL_LONGTERM in gup-fast while gup-slow can still do it. Coherent devmap appears
> to want to block it in all gup.
> 
> On another thread Jason was suggesting about having different pgmap::flags to capture
> these special cases[1] instead of selecting what different pgmap types can do in various
> different places.
> 
> [0] https://lore.kernel.org/linux-mm/6a18179e-65f7-367d-89a9-d5162f10fef0@oracle.com/
> [1] https://lore.kernel.org/linux-mm/20211019160136.GH3686969@ziepe.ca/
>
diff mbox series

Patch

diff --git a/mm/gup.c b/mm/gup.c
index 886d6148d3d0..9c8a075d862d 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_device_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 {