Device coherent pages represent memory on a coherently attached device such
as a GPU which is usually under the control of a driver. These pages should
not be pinned as the driver needs to be able to move pages as required.
Currently this is enforced by failing any attempt to pin a device coherent
page.
A similar problem exists for ZONE_MOVABLE pages. In that case though the
pages are migrated instead of causing failure. There is no reason the
kernel can't migrate device coherent pages so this series implements
migration for device coherent pages so the same strategy of migrate and pin
can be used.
This series depends on the series "Add MEMORY_DEVICE_COHERENT for coherent
device memory mapping"[1] and should apply cleanly on top of that.
[1] - https://lore.kernel.org/linux-mm/[email protected]/
Alex Sierra (1):
tools: add hmm gup test for long term pinned device pages
Alistair Popple (2):
migrate.c: Remove vma check in migrate_vma_setup()
mm/gup.c: Migrate device coherent pages when pinning instead of failing
mm/gup.c | 105 +++++++++++++++++++++++---
mm/migrate.c | 34 ++++----
tools/testing/selftests/vm/Makefile | 2 +-
tools/testing/selftests/vm/hmm-tests.c | 81 ++++++++++++++++++++-
4 files changed, 194 insertions(+), 28 deletions(-)
--
git-series 0.9.1
Currently any attempts to pin a device coherent page will fail. This is
because device coherent pages need to be managed by a device driver, and
pinning them would prevent a driver from migrating them off the device.
However this is no reason to fail pinning of these pages. These are
coherent and accessible from the CPU so can be migrated just like
pinning ZONE_MOVABLE pages. So instead of failing all attempts to pin
them first try migrating them out of ZONE_DEVICE.
Signed-off-by: Alistair Popple <[email protected]>
---
mm/gup.c | 105 ++++++++++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 95 insertions(+), 10 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index f596b93..2cbef54 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1834,6 +1834,60 @@ struct page *get_dump_page(unsigned long addr)
#ifdef CONFIG_MIGRATION
/*
+ * Migrates a device coherent page back to normal memory. Caller should have a
+ * reference on page which will be copied to the new page if migration is
+ * successful or dropped on failure.
+ */
+static struct page *migrate_device_page(struct page *page,
+ unsigned int gup_flags)
+{
+ struct page *dpage;
+ struct migrate_vma args;
+ unsigned long src_pfn, dst_pfn = 0;
+
+ lock_page(page);
+ src_pfn = migrate_pfn(page_to_pfn(page)) | MIGRATE_PFN_MIGRATE;
+ args.src = &src_pfn;
+ args.dst = &dst_pfn;
+ args.cpages = 1;
+ args.npages = 1;
+ args.vma = NULL;
+ migrate_vma_setup(&args);
+ if (!(src_pfn & MIGRATE_PFN_MIGRATE))
+ return NULL;
+
+ dpage = alloc_pages(GFP_USER | __GFP_NOWARN, 0);
+
+ /*
+ * get/pin the new page now so we don't have to retry gup after
+ * migrating. We already have a reference so this should never fail.
+ */
+ if (WARN_ON_ONCE(!try_grab_page(dpage, gup_flags))) {
+ __free_pages(dpage, 0);
+ dpage = NULL;
+ }
+
+ if (dpage) {
+ lock_page(dpage);
+ dst_pfn = migrate_pfn(page_to_pfn(dpage));
+ }
+
+ migrate_vma_pages(&args);
+ if (src_pfn & MIGRATE_PFN_MIGRATE)
+ copy_highpage(dpage, page);
+ migrate_vma_finalize(&args);
+ if (dpage && !(src_pfn & MIGRATE_PFN_MIGRATE)) {
+ if (gup_flags & FOLL_PIN)
+ unpin_user_page(dpage);
+ else
+ put_page(dpage);
+ dpage = NULL;
+ }
+
+ return dpage;
+}
+
+/*
* Check whether all pages are pinnable, if so return number of pages. If some
* pages are not pinnable, migrate them, and unpin all pages. Return zero if
* pages were migrated, or if some pages were not successfully isolated.
@@ -1861,15 +1915,40 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
continue;
prev_head = head;
/*
- * If we get a movable page, since we are going to be pinning
- * these entries, try to move them out if possible.
+ * Device coherent pages are managed by a driver and should not
+ * be pinned indefinitely as it prevents the driver moving the
+ * page. So when trying to pin with FOLL_LONGTERM instead try
+ * migrating page out of device memory.
*/
if (is_dev_private_or_coherent_page(head)) {
+ /*
+ * device private pages will get faulted in during gup
+ * so it shouldn't be possible to see one here.
+ */
WARN_ON_ONCE(is_device_private_page(head));
- ret = -EFAULT;
- goto unpin_pages;
+ WARN_ON_ONCE(PageCompound(head));
+
+ /*
+ * migration will fail if the page is pinned, so convert
+ * the pin on the source page to a normal reference.
+ */
+ if (gup_flags & FOLL_PIN) {
+ get_page(head);
+ unpin_user_page(head);
+ }
+
+ pages[i] = migrate_device_page(head, gup_flags);
+ if (!pages[i]) {
+ ret = -EBUSY;
+ break;
+ }
+ continue;
}
+ /*
+ * If we get a movable page, since we are going to be pinning
+ * these entries, try to move them out if possible.
+ */
if (!is_pinnable_page(head)) {
if (PageHuge(head)) {
if (!isolate_huge_page(head, &movable_page_list))
@@ -1897,16 +1976,22 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
* If list is empty, and no isolation errors, means that all pages are
* in the correct zone.
*/
- if (list_empty(&movable_page_list) && !isolation_error_count)
+ if (!ret && 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 {
- for (i = 0; i < nr_pages; i++)
+ for (i = 0; i < nr_pages; i++)
+ if (!pages[i])
+ continue;
+ else if (gup_flags & FOLL_PIN)
+ unpin_user_page(pages[i]);
+ else
put_page(pages[i]);
+
+ if (ret && !list_empty(&movable_page_list)) {
+ putback_movable_pages(&movable_page_list);
+ return ret;
}
+
if (!list_empty(&movable_page_list)) {
ret = migrate_pages(&movable_page_list, alloc_migration_target,
NULL, (unsigned long)&mtc, MIGRATE_SYNC,
--
git-series 0.9.1
Am 2022-02-01 um 02:05 schrieb Alistair Popple:
> Currently any attempts to pin a device coherent page will fail. This is
> because device coherent pages need to be managed by a device driver, and
> pinning them would prevent a driver from migrating them off the device.
>
> However this is no reason to fail pinning of these pages. These are
> coherent and accessible from the CPU so can be migrated just like
> pinning ZONE_MOVABLE pages. So instead of failing all attempts to pin
> them first try migrating them out of ZONE_DEVICE.
>
> Signed-off-by: Alistair Popple <[email protected]>
Thank you for working on this. I have two questions inline.
Other than that, patches 1 and 2 are
Acked-by: Felix Kuehling <[email protected]>
> ---
> mm/gup.c | 105 ++++++++++++++++++++++++++++++++++++++++++++++++++------
> 1 file changed, 95 insertions(+), 10 deletions(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index f596b93..2cbef54 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1834,6 +1834,60 @@ struct page *get_dump_page(unsigned long addr)
>
> #ifdef CONFIG_MIGRATION
> /*
> + * Migrates a device coherent page back to normal memory. Caller should have a
> + * reference on page which will be copied to the new page if migration is
> + * successful or dropped on failure.
> + */
> +static struct page *migrate_device_page(struct page *page,
> + unsigned int gup_flags)
> +{
> + struct page *dpage;
> + struct migrate_vma args;
> + unsigned long src_pfn, dst_pfn = 0;
> +
> + lock_page(page);
> + src_pfn = migrate_pfn(page_to_pfn(page)) | MIGRATE_PFN_MIGRATE;
> + args.src = &src_pfn;
> + args.dst = &dst_pfn;
> + args.cpages = 1;
> + args.npages = 1;
> + args.vma = NULL;
> + migrate_vma_setup(&args);
> + if (!(src_pfn & MIGRATE_PFN_MIGRATE))
> + return NULL;
> +
> + dpage = alloc_pages(GFP_USER | __GFP_NOWARN, 0);
Don't you need to check dpage for NULL before the try_grab_page call below?
> +
> + /*
> + * get/pin the new page now so we don't have to retry gup after
> + * migrating. We already have a reference so this should never fail.
> + */
> + if (WARN_ON_ONCE(!try_grab_page(dpage, gup_flags))) {
> + __free_pages(dpage, 0);
> + dpage = NULL;
> + }
> +
> + if (dpage) {
> + lock_page(dpage);
> + dst_pfn = migrate_pfn(page_to_pfn(dpage));
> + }
> +
> + migrate_vma_pages(&args);
> + if (src_pfn & MIGRATE_PFN_MIGRATE)
> + copy_highpage(dpage, page);
Can't dpage can be NULL here as well?
Regards,
Felix
> + migrate_vma_finalize(&args);
> + if (dpage && !(src_pfn & MIGRATE_PFN_MIGRATE)) {
> + if (gup_flags & FOLL_PIN)
> + unpin_user_page(dpage);
> + else
> + put_page(dpage);
> + dpage = NULL;
> + }
> +
> + return dpage;
> +}
> +
> +/*
> * Check whether all pages are pinnable, if so return number of pages. If some
> * pages are not pinnable, migrate them, and unpin all pages. Return zero if
> * pages were migrated, or if some pages were not successfully isolated.
> @@ -1861,15 +1915,40 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
> continue;
> prev_head = head;
> /*
> - * If we get a movable page, since we are going to be pinning
> - * these entries, try to move them out if possible.
> + * Device coherent pages are managed by a driver and should not
> + * be pinned indefinitely as it prevents the driver moving the
> + * page. So when trying to pin with FOLL_LONGTERM instead try
> + * migrating page out of device memory.
> */
> if (is_dev_private_or_coherent_page(head)) {
> + /*
> + * device private pages will get faulted in during gup
> + * so it shouldn't be possible to see one here.
> + */
> WARN_ON_ONCE(is_device_private_page(head));
> - ret = -EFAULT;
> - goto unpin_pages;
> + WARN_ON_ONCE(PageCompound(head));
> +
> + /*
> + * migration will fail if the page is pinned, so convert
> + * the pin on the source page to a normal reference.
> + */
> + if (gup_flags & FOLL_PIN) {
> + get_page(head);
> + unpin_user_page(head);
> + }
> +
> + pages[i] = migrate_device_page(head, gup_flags);
> + if (!pages[i]) {
> + ret = -EBUSY;
> + break;
> + }
> + continue;
> }
>
> + /*
> + * If we get a movable page, since we are going to be pinning
> + * these entries, try to move them out if possible.
> + */
> if (!is_pinnable_page(head)) {
> if (PageHuge(head)) {
> if (!isolate_huge_page(head, &movable_page_list))
> @@ -1897,16 +1976,22 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
> * If list is empty, and no isolation errors, means that all pages are
> * in the correct zone.
> */
> - if (list_empty(&movable_page_list) && !isolation_error_count)
> + if (!ret && 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 {
> - for (i = 0; i < nr_pages; i++)
> + for (i = 0; i < nr_pages; i++)
> + if (!pages[i])
> + continue;
> + else if (gup_flags & FOLL_PIN)
> + unpin_user_page(pages[i]);
> + else
> put_page(pages[i]);
> +
> + if (ret && !list_empty(&movable_page_list)) {
> + putback_movable_pages(&movable_page_list);
> + return ret;
> }
> +
> if (!list_empty(&movable_page_list)) {
> ret = migrate_pages(&movable_page_list, alloc_migration_target,
> NULL, (unsigned long)&mtc, MIGRATE_SYNC,
From: Alex Sierra <[email protected]>
The intention is to test device coherent type pages that have been
called through get user pages with PIN_LONGTERM flag set. These pages
should get migrated back to normal system memory.
Signed-off-by: Alex Sierra <[email protected]>
Signed-off-by: Alistair Popple <[email protected]>
---
tools/testing/selftests/vm/Makefile | 2 +-
tools/testing/selftests/vm/hmm-tests.c | 81 +++++++++++++++++++++++++++-
2 files changed, 82 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile
index 1607322..58c8427 100644
--- a/tools/testing/selftests/vm/Makefile
+++ b/tools/testing/selftests/vm/Makefile
@@ -142,7 +142,7 @@ $(OUTPUT)/mlock-random-test $(OUTPUT)/memfd_secret: LDLIBS += -lcap
$(OUTPUT)/gup_test: ../../../../mm/gup_test.h
-$(OUTPUT)/hmm-tests: local_config.h
+$(OUTPUT)/hmm-tests: local_config.h ../../../../mm/gup_test.h
# HMM_EXTRA_LIBS may get set in local_config.mk, or it may be left empty.
$(OUTPUT)/hmm-tests: LDLIBS += $(HMM_EXTRA_LIBS)
diff --git a/tools/testing/selftests/vm/hmm-tests.c b/tools/testing/selftests/vm/hmm-tests.c
index 84ec8c4..11b83a8 100644
--- a/tools/testing/selftests/vm/hmm-tests.c
+++ b/tools/testing/selftests/vm/hmm-tests.c
@@ -36,6 +36,7 @@
* in the usual include/uapi/... directory.
*/
#include "../../../../lib/test_hmm_uapi.h"
+#include "../../../../mm/gup_test.h"
struct hmm_buffer {
void *ptr;
@@ -60,6 +61,8 @@ enum {
#define NTIMES 10
#define ALIGN(x, a) (((x) + (a - 1)) & (~((a) - 1)))
+/* Just the flags we need, copied from mm.h: */
+#define FOLL_WRITE 0x01 /* check pte is writable */
FIXTURE(hmm)
{
@@ -1766,4 +1769,82 @@ TEST_F(hmm, exclusive_cow)
hmm_buffer_free(buffer);
}
+/*
+ * Test get user device pages through gup_test. Setting PIN_LONGTERM flag.
+ * This should trigger a migration back to system memory for both, private
+ * and coherent type pages.
+ * This test makes use of gup_test module. Make sure GUP_TEST_CONFIG is added
+ * to your configuration before you run it.
+ */
+TEST_F(hmm, hmm_gup_test)
+{
+ struct hmm_buffer *buffer;
+ struct gup_test gup;
+ int gup_fd;
+ unsigned long npages;
+ unsigned long size;
+ unsigned long i;
+ int *ptr;
+ int ret;
+ unsigned char *m;
+
+ gup_fd = open("/sys/kernel/debug/gup_test", O_RDWR);
+ if (gup_fd == -1)
+ SKIP(return, "Skipping test, could not find gup_test driver");
+
+ npages = 4;
+ ASSERT_NE(npages, 0);
+ size = npages << self->page_shift;
+
+ buffer = malloc(sizeof(*buffer));
+ ASSERT_NE(buffer, NULL);
+
+ buffer->fd = -1;
+ buffer->size = size;
+ buffer->mirror = malloc(size);
+ ASSERT_NE(buffer->mirror, NULL);
+
+ buffer->ptr = mmap(NULL, size,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS,
+ buffer->fd, 0);
+ ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+ /* Initialize buffer in system memory. */
+ for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+ ptr[i] = i;
+
+ /* Migrate memory to device. */
+ ret = hmm_migrate_sys_to_dev(self->fd, buffer, npages);
+ ASSERT_EQ(ret, 0);
+ ASSERT_EQ(buffer->cpages, npages);
+ /* Check what the device read. */
+ for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+ ASSERT_EQ(ptr[i], i);
+
+ gup.nr_pages_per_call = npages;
+ gup.addr = (unsigned long)buffer->ptr;
+ gup.gup_flags = FOLL_WRITE;
+ gup.size = size;
+ /*
+ * Calling gup_test ioctl. It will try to PIN_LONGTERM these device pages
+ * causing a migration back to system memory for both, private and coherent
+ * type pages.
+ */
+ if (ioctl(gup_fd, PIN_LONGTERM_BENCHMARK, &gup)) {
+ perror("ioctl on PIN_LONGTERM_BENCHMARK\n");
+ goto out_test;
+ }
+
+ /* Take snapshot to make sure pages have been migrated to sys memory */
+ ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_SNAPSHOT, buffer, npages);
+ ASSERT_EQ(ret, 0);
+ ASSERT_EQ(buffer->cpages, npages);
+ m = buffer->mirror;
+ for (i = 0; i < npages; i++)
+ ASSERT_EQ(m[i], HMM_DMIRROR_PROT_WRITE);
+out_test:
+ close(gup_fd);
+ hmm_buffer_free(buffer);
+}
TEST_HARNESS_MAIN
--
git-series 0.9.1
migrate_vma_setup() checks that a valid vma is passed so that the page
tables can be walked to find the pfns associated with a given address
range. However in some cases the pfns are already known, such as when
migrating device coherent pages during pin_user_pages() meaning a valid
vma isn't required.
Signed-off-by: Alistair Popple <[email protected]>
---
mm/migrate.c | 34 +++++++++++++++++-----------------
1 file changed, 17 insertions(+), 17 deletions(-)
diff --git a/mm/migrate.c b/mm/migrate.c
index d3cc358..31ba8ca 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2581,24 +2581,24 @@ int migrate_vma_setup(struct migrate_vma *args)
args->start &= PAGE_MASK;
args->end &= PAGE_MASK;
- if (!args->vma || is_vm_hugetlb_page(args->vma) ||
- (args->vma->vm_flags & VM_SPECIAL) || vma_is_dax(args->vma))
- return -EINVAL;
- if (nr_pages <= 0)
- return -EINVAL;
- if (args->start < args->vma->vm_start ||
- args->start >= args->vma->vm_end)
- return -EINVAL;
- if (args->end <= args->vma->vm_start || args->end > args->vma->vm_end)
- return -EINVAL;
if (!args->src || !args->dst)
return -EINVAL;
-
- memset(args->src, 0, sizeof(*args->src) * nr_pages);
- args->cpages = 0;
- args->npages = 0;
-
- migrate_vma_collect(args);
+ if (args->vma) {
+ if (is_vm_hugetlb_page(args->vma) ||
+ (args->vma->vm_flags & VM_SPECIAL) || vma_is_dax(args->vma))
+ return -EINVAL;
+ if (args->start < args->vma->vm_start ||
+ args->start >= args->vma->vm_end)
+ return -EINVAL;
+ if (args->end <= args->vma->vm_start || args->end > args->vma->vm_end)
+ return -EINVAL;
+
+ memset(args->src, 0, sizeof(*args->src) * nr_pages);
+ args->cpages = 0;
+ args->npages = 0;
+
+ migrate_vma_collect(args);
+ }
if (args->cpages)
migrate_vma_unmap(args);
@@ -2783,7 +2783,7 @@ void migrate_vma_pages(struct migrate_vma *migrate)
continue;
}
- if (!page) {
+ if (!page && migrate->vma) {
if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE))
continue;
if (!notified) {
--
git-series 0.9.1
On Wednesday, 2 February 2022 2:03:01 AM AEDT Felix Kuehling wrote:
>
> Am 2022-02-01 um 02:05 schrieb Alistair Popple:
> > Currently any attempts to pin a device coherent page will fail. This is
> > because device coherent pages need to be managed by a device driver, and
> > pinning them would prevent a driver from migrating them off the device.
> >
> > However this is no reason to fail pinning of these pages. These are
> > coherent and accessible from the CPU so can be migrated just like
> > pinning ZONE_MOVABLE pages. So instead of failing all attempts to pin
> > them first try migrating them out of ZONE_DEVICE.
> >
> > Signed-off-by: Alistair Popple <[email protected]>
>
> Thank you for working on this. I have two questions inline.
>
> Other than that, patches 1 and 2 are
>
> Acked-by: Felix Kuehling <[email protected]>
>
>
> > ---
> > mm/gup.c | 105 ++++++++++++++++++++++++++++++++++++++++++++++++++------
> > 1 file changed, 95 insertions(+), 10 deletions(-)
> >
> > diff --git a/mm/gup.c b/mm/gup.c
> > index f596b93..2cbef54 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -1834,6 +1834,60 @@ struct page *get_dump_page(unsigned long addr)
> >
> > #ifdef CONFIG_MIGRATION
> > /*
> > + * Migrates a device coherent page back to normal memory. Caller should have a
> > + * reference on page which will be copied to the new page if migration is
> > + * successful or dropped on failure.
> > + */
> > +static struct page *migrate_device_page(struct page *page,
> > + unsigned int gup_flags)
> > +{
> > + struct page *dpage;
> > + struct migrate_vma args;
> > + unsigned long src_pfn, dst_pfn = 0;
> > +
> > + lock_page(page);
> > + src_pfn = migrate_pfn(page_to_pfn(page)) | MIGRATE_PFN_MIGRATE;
> > + args.src = &src_pfn;
> > + args.dst = &dst_pfn;
> > + args.cpages = 1;
> > + args.npages = 1;
> > + args.vma = NULL;
> > + migrate_vma_setup(&args);
> > + if (!(src_pfn & MIGRATE_PFN_MIGRATE))
> > + return NULL;
> > +
> > + dpage = alloc_pages(GFP_USER | __GFP_NOWARN, 0);
>
> Don't you need to check dpage for NULL before the try_grab_page call below?
Yes, thanks for pointing that out. Will fix for v2.
> > +
> > + /*
> > + * get/pin the new page now so we don't have to retry gup after
> > + * migrating. We already have a reference so this should never fail.
> > + */
> > + if (WARN_ON_ONCE(!try_grab_page(dpage, gup_flags))) {
> > + __free_pages(dpage, 0);
> > + dpage = NULL;
> > + }
> > +
> > + if (dpage) {
> > + lock_page(dpage);
> > + dst_pfn = migrate_pfn(page_to_pfn(dpage));
> > + }
> > +
> > + migrate_vma_pages(&args);
> > + if (src_pfn & MIGRATE_PFN_MIGRATE)
> > + copy_highpage(dpage, page);
>
> Can't dpage can be NULL here as well?
No - migrate_vma_pages() will clear src_pfn & MIGRATE_PFN_MIGRATE if no
destination page is provided in dst_pfn.
> Regards,
> Felix
>
>
> > + migrate_vma_finalize(&args);
> > + if (dpage && !(src_pfn & MIGRATE_PFN_MIGRATE)) {
> > + if (gup_flags & FOLL_PIN)
> > + unpin_user_page(dpage);
> > + else
> > + put_page(dpage);
> > + dpage = NULL;
> > + }
> > +
> > + return dpage;
> > +}
> > +
> > +/*
> > * Check whether all pages are pinnable, if so return number of pages. If some
> > * pages are not pinnable, migrate them, and unpin all pages. Return zero if
> > * pages were migrated, or if some pages were not successfully isolated.
> > @@ -1861,15 +1915,40 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
> > continue;
> > prev_head = head;
> > /*
> > - * If we get a movable page, since we are going to be pinning
> > - * these entries, try to move them out if possible.
> > + * Device coherent pages are managed by a driver and should not
> > + * be pinned indefinitely as it prevents the driver moving the
> > + * page. So when trying to pin with FOLL_LONGTERM instead try
> > + * migrating page out of device memory.
> > */
> > if (is_dev_private_or_coherent_page(head)) {
> > + /*
> > + * device private pages will get faulted in during gup
> > + * so it shouldn't be possible to see one here.
> > + */
> > WARN_ON_ONCE(is_device_private_page(head));
> > - ret = -EFAULT;
> > - goto unpin_pages;
> > + WARN_ON_ONCE(PageCompound(head));
> > +
> > + /*
> > + * migration will fail if the page is pinned, so convert
> > + * the pin on the source page to a normal reference.
> > + */
> > + if (gup_flags & FOLL_PIN) {
> > + get_page(head);
> > + unpin_user_page(head);
> > + }
> > +
> > + pages[i] = migrate_device_page(head, gup_flags);
> > + if (!pages[i]) {
> > + ret = -EBUSY;
> > + break;
> > + }
> > + continue;
> > }
> >
> > + /*
> > + * If we get a movable page, since we are going to be pinning
> > + * these entries, try to move them out if possible.
> > + */
> > if (!is_pinnable_page(head)) {
> > if (PageHuge(head)) {
> > if (!isolate_huge_page(head, &movable_page_list))
> > @@ -1897,16 +1976,22 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
> > * If list is empty, and no isolation errors, means that all pages are
> > * in the correct zone.
> > */
> > - if (list_empty(&movable_page_list) && !isolation_error_count)
> > + if (!ret && 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 {
> > - for (i = 0; i < nr_pages; i++)
> > + for (i = 0; i < nr_pages; i++)
> > + if (!pages[i])
> > + continue;
> > + else if (gup_flags & FOLL_PIN)
> > + unpin_user_page(pages[i]);
> > + else
> > put_page(pages[i]);
> > +
> > + if (ret && !list_empty(&movable_page_list)) {
> > + putback_movable_pages(&movable_page_list);
> > + return ret;
> > }
> > +
> > if (!list_empty(&movable_page_list)) {
> > ret = migrate_pages(&movable_page_list, alloc_migration_target,
> > NULL, (unsigned long)&mtc, MIGRATE_SYNC,
>