fs/proc/task_mmu.c | 1 - 1 file changed, 1 deletion(-)
pagemap_pmd_range_thp() warns if a non-present PMD is not a migration
entry. This became false once device-private entries at the PMD level were
added.
One can hit the warning by patching hmm-tests.c with the following:
diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
index e1c8a679a4cf3..7f0a3384f3c5f 100644
--- a/tools/testing/selftests/mm/hmm-tests.c
+++ b/tools/testing/selftests/mm/hmm-tests.c
@@ -209,6 +209,37 @@ static int hmm_dmirror_cmd(int fd,
return 0;
}
+static int hmm_read_self_pagemap(void *addr, unsigned long npages,
+ unsigned long page_size)
+{
+ const size_t entry_size = sizeof(uint64_t);
+ const off_t offset = ((uintptr_t)addr / page_size) * entry_size;
+ uint64_t *entries;
+ ssize_t nread;
+ int fd;
+
+ entries = malloc(npages * entry_size);
+ if (!entries)
+ return -ENOMEM;
+
+ fd = open("/proc/self/pagemap", O_RDONLY);
+ if (fd < 0) {
+ free(entries);
+ return -errno;
+ }
+
+ nread = pread(fd, entries, npages * entry_size, offset);
+ close(fd);
+ free(entries);
+
+ if (nread < 0)
+ return -errno;
+ if ((size_t)nread != npages * entry_size)
+ return -EIO;
+
+ return 0;
+}
+
static void hmm_buffer_free(struct hmm_buffer *buffer)
{
if (buffer == NULL)
@@ -2314,6 +2345,10 @@ TEST_F(hmm, migrate_anon_huge_fault)
ASSERT_EQ(ret, 0);
ASSERT_EQ(buffer->cpages, npages);
+ /* Exercise pagemap on a PMD device-private entry. */
+ ret = hmm_read_self_pagemap(buffer->ptr, npages, self->page_size);
+ ASSERT_EQ(ret, 0);
+
/* Check what the device read. */
for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
ASSERT_EQ(ptr[i], i);
Therefore, remove the stale migration-only assertion.
Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages")
Cc: stable@vger.kernel.org
Signed-off-by: Dev Jain <dev.jain@arm.com>
---
Applies on mm-unstable (404fb4f38e8f).
fs/proc/task_mmu.c | 1 -
1 file changed, 1 deletion(-)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 1e3a15bf46f4e..58938e62154d9 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -2129,7 +2129,6 @@ static int pagemap_pmd_range_thp(pmd_t *pmdp, unsigned long addr,
flags |= PM_SOFT_DIRTY;
if (pmd_swp_uffd_wp(pmd))
flags |= PM_UFFD_WP;
- VM_WARN_ON_ONCE(!pmd_is_migration_entry(pmd));
page = softleaf_to_page(entry);
}
--
2.43.0On Fri, May 29, 2026 at 11:17:03AM +0000, Dev Jain wrote:
> pagemap_pmd_range_thp() warns if a non-present PMD is not a migration
> entry. This became false once device-private entries at the PMD level were
> added.
>
> One can hit the warning by patching hmm-tests.c with the following:
>
> diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
> index e1c8a679a4cf3..7f0a3384f3c5f 100644
> --- a/tools/testing/selftests/mm/hmm-tests.c
> +++ b/tools/testing/selftests/mm/hmm-tests.c
> @@ -209,6 +209,37 @@ static int hmm_dmirror_cmd(int fd,
> return 0;
> }
>
> +static int hmm_read_self_pagemap(void *addr, unsigned long npages,
> + unsigned long page_size)
> +{
> + const size_t entry_size = sizeof(uint64_t);
> + const off_t offset = ((uintptr_t)addr / page_size) * entry_size;
> + uint64_t *entries;
> + ssize_t nread;
> + int fd;
> +
> + entries = malloc(npages * entry_size);
> + if (!entries)
> + return -ENOMEM;
> +
> + fd = open("/proc/self/pagemap", O_RDONLY);
> + if (fd < 0) {
> + free(entries);
> + return -errno;
> + }
> +
> + nread = pread(fd, entries, npages * entry_size, offset);
> + close(fd);
> + free(entries);
> +
> + if (nread < 0)
> + return -errno;
> + if ((size_t)nread != npages * entry_size)
> + return -EIO;
> +
> + return 0;
> +}
> +
> static void hmm_buffer_free(struct hmm_buffer *buffer)
> {
> if (buffer == NULL)
> @@ -2314,6 +2345,10 @@ TEST_F(hmm, migrate_anon_huge_fault)
> ASSERT_EQ(ret, 0);
> ASSERT_EQ(buffer->cpages, npages);
>
> + /* Exercise pagemap on a PMD device-private entry. */
> + ret = hmm_read_self_pagemap(buffer->ptr, npages, self->page_size);
> + ASSERT_EQ(ret, 0);
> +
> /* Check what the device read. */
> for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> ASSERT_EQ(ptr[i], i);
>
>
> Therefore, remove the stale migration-only assertion.
>
> Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages")
> Cc: stable@vger.kernel.org
> Signed-off-by: Dev Jain <dev.jain@arm.com>
LGTM,
Reviewed-by: Oscar Salvador (SUSE) <osalvador@kernel.org>
--
Oscar Salvador
SUSE Labs
On 5/29/26 13:17, Dev Jain wrote:
> pagemap_pmd_range_thp() warns if a non-present PMD is not a migration
> entry. This became false once device-private entries at the PMD level were
> added.
>
> One can hit the warning by patching hmm-tests.c with the following:
>
> diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
> index e1c8a679a4cf3..7f0a3384f3c5f 100644
> --- a/tools/testing/selftests/mm/hmm-tests.c
> +++ b/tools/testing/selftests/mm/hmm-tests.c
> @@ -209,6 +209,37 @@ static int hmm_dmirror_cmd(int fd,
> return 0;
> }
>
> +static int hmm_read_self_pagemap(void *addr, unsigned long npages,
> + unsigned long page_size)
> +{
> + const size_t entry_size = sizeof(uint64_t);
> + const off_t offset = ((uintptr_t)addr / page_size) * entry_size;
> + uint64_t *entries;
> + ssize_t nread;
> + int fd;
> +
> + entries = malloc(npages * entry_size);
> + if (!entries)
> + return -ENOMEM;
> +
> + fd = open("/proc/self/pagemap", O_RDONLY);
> + if (fd < 0) {
> + free(entries);
> + return -errno;
> + }
> +
> + nread = pread(fd, entries, npages * entry_size, offset);
> + close(fd);
> + free(entries);
> +
> + if (nread < 0)
> + return -errno;
> + if ((size_t)nread != npages * entry_size)
> + return -EIO;
> +
> + return 0;
> +}
> +
> static void hmm_buffer_free(struct hmm_buffer *buffer)
> {
> if (buffer == NULL)
> @@ -2314,6 +2345,10 @@ TEST_F(hmm, migrate_anon_huge_fault)
> ASSERT_EQ(ret, 0);
> ASSERT_EQ(buffer->cpages, npages);
>
> + /* Exercise pagemap on a PMD device-private entry. */
> + ret = hmm_read_self_pagemap(buffer->ptr, npages, self->page_size);
> + ASSERT_EQ(ret, 0);
> +
> /* Check what the device read. */
> for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> ASSERT_EQ(ptr[i], i);
>
>
> Therefore, remove the stale migration-only assertion.
>
> Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages")
> Cc: stable@vger.kernel.org
> Signed-off-by: Dev Jain <dev.jain@arm.com>
> ---
> Applies on mm-unstable (404fb4f38e8f).
>
> fs/proc/task_mmu.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 1e3a15bf46f4e..58938e62154d9 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -2129,7 +2129,6 @@ static int pagemap_pmd_range_thp(pmd_t *pmdp, unsigned long addr,
> flags |= PM_SOFT_DIRTY;
> if (pmd_swp_uffd_wp(pmd))
> flags |= PM_UFFD_WP;
> - VM_WARN_ON_ONCE(!pmd_is_migration_entry(pmd));
> page = softleaf_to_page(entry);
> }
>
The whole thp_migration_supported() guard is a bit shaky, right?
I guess device-private entries currently imply thp_migration_supported(), but
that thp_migration_supported() check is really questionable and should likely
just go away (else if -> else).
Staring at pte_to_pagemap_entry(), likely we'd also want
if (softleaf_has_pfn(entry))
page = softleaf_to_page(entry);
to prepare for PMD swap entries.
Anyhow, both are unrelated (can you send patches to clean it up?)
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
--
Cheers,
David
On Sun, May 31, 2026 at 09:11:53PM +0200, David Hildenbrand (Arm) wrote: > The whole thp_migration_supported() guard is a bit shaky, right? > > I guess device-private entries currently imply thp_migration_supported(), but > that thp_migration_supported() check is really questionable and should likely > just go away (else if -> else). > > Staring at pte_to_pagemap_entry(), likely we'd also want > > if (softleaf_has_pfn(entry)) > page = softleaf_to_page(entry); > > to prepare for PMD swap entries. Yes, that is what I was doing for non-present PMDs when implementing the new API [1]. [1] https://lore.kernel.org/linux-mm/20260525165528.184397-5-osalvador@suse.de/ -- Oscar Salvador SUSE Labs
On 01/06/26 12:41 am, David Hildenbrand (Arm) wrote:
> On 5/29/26 13:17, Dev Jain wrote:
>> pagemap_pmd_range_thp() warns if a non-present PMD is not a migration
>> entry. This became false once device-private entries at the PMD level were
>> added.
>>
>> One can hit the warning by patching hmm-tests.c with the following:
>>
>> diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
>> index e1c8a679a4cf3..7f0a3384f3c5f 100644
>> --- a/tools/testing/selftests/mm/hmm-tests.c
>> +++ b/tools/testing/selftests/mm/hmm-tests.c
>> @@ -209,6 +209,37 @@ static int hmm_dmirror_cmd(int fd,
>> return 0;
>> }
>>
>> +static int hmm_read_self_pagemap(void *addr, unsigned long npages,
>> + unsigned long page_size)
>> +{
>> + const size_t entry_size = sizeof(uint64_t);
>> + const off_t offset = ((uintptr_t)addr / page_size) * entry_size;
>> + uint64_t *entries;
>> + ssize_t nread;
>> + int fd;
>> +
>> + entries = malloc(npages * entry_size);
>> + if (!entries)
>> + return -ENOMEM;
>> +
>> + fd = open("/proc/self/pagemap", O_RDONLY);
>> + if (fd < 0) {
>> + free(entries);
>> + return -errno;
>> + }
>> +
>> + nread = pread(fd, entries, npages * entry_size, offset);
>> + close(fd);
>> + free(entries);
>> +
>> + if (nread < 0)
>> + return -errno;
>> + if ((size_t)nread != npages * entry_size)
>> + return -EIO;
>> +
>> + return 0;
>> +}
>> +
>> static void hmm_buffer_free(struct hmm_buffer *buffer)
>> {
>> if (buffer == NULL)
>> @@ -2314,6 +2345,10 @@ TEST_F(hmm, migrate_anon_huge_fault)
>> ASSERT_EQ(ret, 0);
>> ASSERT_EQ(buffer->cpages, npages);
>>
>> + /* Exercise pagemap on a PMD device-private entry. */
>> + ret = hmm_read_self_pagemap(buffer->ptr, npages, self->page_size);
>> + ASSERT_EQ(ret, 0);
>> +
>> /* Check what the device read. */
>> for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
>> ASSERT_EQ(ptr[i], i);
>>
>>
>
>
>> Therefore, remove the stale migration-only assertion.
>>
>> Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Dev Jain <dev.jain@arm.com>
>> ---
>> Applies on mm-unstable (404fb4f38e8f).
>>
>> fs/proc/task_mmu.c | 1 -
>> 1 file changed, 1 deletion(-)
>>
>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
>> index 1e3a15bf46f4e..58938e62154d9 100644
>> --- a/fs/proc/task_mmu.c
>> +++ b/fs/proc/task_mmu.c
>> @@ -2129,7 +2129,6 @@ static int pagemap_pmd_range_thp(pmd_t *pmdp, unsigned long addr,
>> flags |= PM_SOFT_DIRTY;
>> if (pmd_swp_uffd_wp(pmd))
>> flags |= PM_UFFD_WP;
>> - VM_WARN_ON_ONCE(!pmd_is_migration_entry(pmd));
>> page = softleaf_to_page(entry);
>> }
>>
>
> The whole thp_migration_supported() guard is a bit shaky, right?
I think if you remove this, then you will trigger a WARN_ON in softleaf_to_page(),
for the case of !CONFIG_ARCH_ENABLE_THP_MIGRATION.
>
> I guess device-private entries currently imply thp_migration_supported(), but
> that thp_migration_supported() check is really questionable and should likely
> just go away (else if -> else).
>
> Staring at pte_to_pagemap_entry(), likely we'd also want
>
> if (softleaf_has_pfn(entry))
> page = softleaf_to_page(entry);
>
> to prepare for PMD swap entries.
Correct, and this is done in
https://lore.kernel.org/all/20260427100553.2754667-4-usama.arif@linux.dev/
I think in addition to that, Usama can also remove the thp_migration_supported() check.
>
>
> Anyhow, both are unrelated (can you send patches to clean it up?)
>
> Acked-by: David Hildenbrand (Arm) <david@kernel.org>
>
On 6/1/26 06:56, Dev Jain wrote:
>
>
> On 01/06/26 12:41 am, David Hildenbrand (Arm) wrote:
>> On 5/29/26 13:17, Dev Jain wrote:
>>> pagemap_pmd_range_thp() warns if a non-present PMD is not a migration
>>> entry. This became false once device-private entries at the PMD level were
>>> added.
>>>
>>> One can hit the warning by patching hmm-tests.c with the following:
>>>
>>> diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
>>> index e1c8a679a4cf3..7f0a3384f3c5f 100644
>>> --- a/tools/testing/selftests/mm/hmm-tests.c
>>> +++ b/tools/testing/selftests/mm/hmm-tests.c
>>> @@ -209,6 +209,37 @@ static int hmm_dmirror_cmd(int fd,
>>> return 0;
>>> }
>>>
>>> +static int hmm_read_self_pagemap(void *addr, unsigned long npages,
>>> + unsigned long page_size)
>>> +{
>>> + const size_t entry_size = sizeof(uint64_t);
>>> + const off_t offset = ((uintptr_t)addr / page_size) * entry_size;
>>> + uint64_t *entries;
>>> + ssize_t nread;
>>> + int fd;
>>> +
>>> + entries = malloc(npages * entry_size);
>>> + if (!entries)
>>> + return -ENOMEM;
>>> +
>>> + fd = open("/proc/self/pagemap", O_RDONLY);
>>> + if (fd < 0) {
>>> + free(entries);
>>> + return -errno;
>>> + }
>>> +
>>> + nread = pread(fd, entries, npages * entry_size, offset);
>>> + close(fd);
>>> + free(entries);
>>> +
>>> + if (nread < 0)
>>> + return -errno;
>>> + if ((size_t)nread != npages * entry_size)
>>> + return -EIO;
>>> +
>>> + return 0;
>>> +}
>>> +
>>> static void hmm_buffer_free(struct hmm_buffer *buffer)
>>> {
>>> if (buffer == NULL)
>>> @@ -2314,6 +2345,10 @@ TEST_F(hmm, migrate_anon_huge_fault)
>>> ASSERT_EQ(ret, 0);
>>> ASSERT_EQ(buffer->cpages, npages);
>>>
>>> + /* Exercise pagemap on a PMD device-private entry. */
>>> + ret = hmm_read_self_pagemap(buffer->ptr, npages, self->page_size);
>>> + ASSERT_EQ(ret, 0);
>>> +
>>> /* Check what the device read. */
>>> for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
>>> ASSERT_EQ(ptr[i], i);
>>>
>>>
>>
>>
>>> Therefore, remove the stale migration-only assertion.
>>>
>>> Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages")
>>> Cc: stable@vger.kernel.org
>>> Signed-off-by: Dev Jain <dev.jain@arm.com>
>>> ---
>>> Applies on mm-unstable (404fb4f38e8f).
>>>
>>> fs/proc/task_mmu.c | 1 -
>>> 1 file changed, 1 deletion(-)
>>>
>>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
>>> index 1e3a15bf46f4e..58938e62154d9 100644
>>> --- a/fs/proc/task_mmu.c
>>> +++ b/fs/proc/task_mmu.c
>>> @@ -2129,7 +2129,6 @@ static int pagemap_pmd_range_thp(pmd_t *pmdp, unsigned long addr,
>>> flags |= PM_SOFT_DIRTY;
>>> if (pmd_swp_uffd_wp(pmd))
>>> flags |= PM_UFFD_WP;
>>> - VM_WARN_ON_ONCE(!pmd_is_migration_entry(pmd));
>>> page = softleaf_to_page(entry);
>>> }
>>>
>>
>> The whole thp_migration_supported() guard is a bit shaky, right?
>
> I think if you remove this, then you will trigger a WARN_ON in softleaf_to_page(),
> for the case of !CONFIG_ARCH_ENABLE_THP_MIGRATION.
Right, what I noted below.
Right now it's all a bit hacked on top of initial migration entry support.
>>
>> I guess device-private entries currently imply thp_migration_supported(), but
>> that thp_migration_supported() check is really questionable and should likely
>> just go away (else if -> else).
>>
>> Staring at pte_to_pagemap_entry(), likely we'd also want
>>
>> if (softleaf_has_pfn(entry))
>> page = softleaf_to_page(entry);
>>
>> to prepare for PMD swap entries.
>
> Correct, and this is done in
> https://lore.kernel.org/all/20260427100553.2754667-4-usama.arif@linux.dev/
>
> I think in addition to that, Usama can also remove the thp_migration_supported() check.
Yes, that one should go away.
--
Cheers,
David
On Fri, May 29, 2026 at 11:17:03AM +0000, Dev Jain wrote:
> pagemap_pmd_range_thp() warns if a non-present PMD is not a migration
> entry. This became false once device-private entries at the PMD level were
> added.
>
> One can hit the warning by patching hmm-tests.c with the following:
>
> diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
> index e1c8a679a4cf3..7f0a3384f3c5f 100644
> --- a/tools/testing/selftests/mm/hmm-tests.c
> +++ b/tools/testing/selftests/mm/hmm-tests.c
> @@ -209,6 +209,37 @@ static int hmm_dmirror_cmd(int fd,
> return 0;
> }
>
> +static int hmm_read_self_pagemap(void *addr, unsigned long npages,
> + unsigned long page_size)
> +{
> + const size_t entry_size = sizeof(uint64_t);
> + const off_t offset = ((uintptr_t)addr / page_size) * entry_size;
> + uint64_t *entries;
> + ssize_t nread;
> + int fd;
> +
> + entries = malloc(npages * entry_size);
> + if (!entries)
> + return -ENOMEM;
> +
> + fd = open("/proc/self/pagemap", O_RDONLY);
> + if (fd < 0) {
> + free(entries);
> + return -errno;
> + }
> +
> + nread = pread(fd, entries, npages * entry_size, offset);
> + close(fd);
> + free(entries);
> +
> + if (nread < 0)
> + return -errno;
> + if ((size_t)nread != npages * entry_size)
> + return -EIO;
> +
> + return 0;
> +}
> +
> static void hmm_buffer_free(struct hmm_buffer *buffer)
> {
> if (buffer == NULL)
> @@ -2314,6 +2345,10 @@ TEST_F(hmm, migrate_anon_huge_fault)
> ASSERT_EQ(ret, 0);
> ASSERT_EQ(buffer->cpages, npages);
>
> + /* Exercise pagemap on a PMD device-private entry. */
> + ret = hmm_read_self_pagemap(buffer->ptr, npages, self->page_size);
> + ASSERT_EQ(ret, 0);
> +
> /* Check what the device read. */
> for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> ASSERT_EQ(ptr[i], i);
Thanks for this!
though, hmm it really feels like you maybe want to add this as a test and
make this a series :)
Andrew is usually fine with adding tests as part of a fix I believe!
>
>
> Therefore, remove the stale migration-only assertion.
>
> Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages")
> Cc: stable@vger.kernel.org
> Signed-off-by: Dev Jain <dev.jain@arm.com>
The logic does seem sense, it does seem like something of an oversight here
and I can repro the assert (though I have to fix something else first on my
system, patch incoming for that...!)
> ---
> Applies on mm-unstable (404fb4f38e8f).
>
> fs/proc/task_mmu.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 1e3a15bf46f4e..58938e62154d9 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -2129,7 +2129,6 @@ static int pagemap_pmd_range_thp(pmd_t *pmdp, unsigned long addr,
> flags |= PM_SOFT_DIRTY;
> if (pmd_swp_uffd_wp(pmd))
> flags |= PM_UFFD_WP;
> - VM_WARN_ON_ONCE(!pmd_is_migration_entry(pmd));
> page = softleaf_to_page(entry);
> }
>
> --
> 2.43.0
>
Cheers, Lorenzo
On Fri, 29 May 2026 17:45:24 +0100 Lorenzo Stoakes <ljs@kernel.org> wrote: > > + /* Exercise pagemap on a PMD device-private entry. */ > > + ret = hmm_read_self_pagemap(buffer->ptr, npages, self->page_size); > > + ASSERT_EQ(ret, 0); > > + > > /* Check what the device read. */ > > for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i) > > ASSERT_EQ(ptr[i], i); > > Thanks for this! > > though, hmm it really feels like you maybe want to add this as a test and > make this a series :) yes please!
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