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 <[email protected]>
---
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;
+ }
+
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 {
--
2.32.0
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 <[email protected]>
> ---
> 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/[email protected]/
[1] https://lore.kernel.org/linux-mm/[email protected]/
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 <[email protected]>
> > ---
> > 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/[email protected]/
> [1] https://lore.kernel.org/linux-mm/[email protected]/
>