Hi José
Am 03.07.26 um 11:00 schrieb José Expósito:
Hi Thomas,
Thanks for your review.
On Fri, Jul 03, 2026 at 08:53:30AM +0200, Thomas Zimmermann wrote:
Hi
Am 03.07.26 um 08:34 schrieb José Expósito:
Two drm_gem_shmem KUnit tests, drm_gem_shmem_test_get_pages_sgt() and
drm_gem_shmem_test_purge(), intermittently fail on ppc64le and s390x CI
with a DMA address overflow warning followed by -EIO:
DMA addr 0x00000001130b0000+65536 overflow (mask ffffffff, bus limit 0).
Expected sgt is not error, but is: -5
Both tests call `drm_gem_shmem_get_pages_sgt()`, which internally pins
backing pages and DMA-maps them via `dma_map_sgtable()`. The DMA mapping
path is:
drm_gem_shmem_test_purge()
drm_gem_shmem_get_pages_sgt()
drm_gem_shmem_get_pages_sgt_locked() [drm_gem_shmem_helper.c]
dma_map_sgtable() [mapping.c]
__dma_map_sg_attrs()
dma_direct_map_sg() [direct.c]
dma_direct_map_phys() [kernel/dma/direct.h]
dma_capable() Checks addr against DMA mask
-> FAILS: addr > 0xFFFFFFFF
KUnit devices are initialized with a 32-bit DMA mask
(`DMA_BIT_MASK(32)`) in `lib/kunit/device.c`. On systems where the kernel
allocates backing pages at physical addresses above 4GB, `dma_capable()`
returns false because the address exceeds the 32-bit mask. The `dma_set_mask()`
function updates `*dev->dma_mask` to the given value; setting it to
`DMA_BIT_MASK(64)` allows any physical address to pass the check.
The failure is intermittent because pages may or may not be allocated
above 4GB on any given run depend on memory pressure.
A third test in the same suite, `drm_gem_shmem_test_obj_create_private`,
already calls `dma_set_mask(drm_dev->dev, DMA_BIT_MASK(64))` before its
DMA mapping. This series applies the same fix to the two remaining tests.
Instead of doing whack-a-mole, is it possible to move the existing fix from
drm_gem_shmem_test_obj_create_private() to _test_init at [1] ? The DMA mask
would then be the same on all tests. [1]
https://elixir.bootlin.com/linux/v7.1.2/source/drivers/gpu/drm/tests/drm_gem_shmem_test.c#L359
Yes, I think it is possible. However, this is an intermittent failure that
I couldn't reproduce locally and I tried to reduce as much as possible the
risk of regression limitting the change to the 2 affected tests.
I'm afraid I don't have enough knoledge about GEM's internals to know if moving
the fix to the init function could introduce unwanted side-effects in the other
tests. If you think it'd be safe, I'll trust you and move it.
Please do. I don't see why it should not work, and it's an easy revert
it doesn't.
Best regards
Thomas
Jose
PS - Next week I'll be away from keyboard, so any change would need to wait a
bit
Best regards Thomas
José Expósito (2):
drm/tests: shmem: Set DMA mask to 64-bit in
drm_gem_shmem_test_get_pages_sgt
drm/tests: shmem: Set DMA mask to 64-bit in drm_gem_shmem_test_purge
drivers/gpu/drm/tests/drm_gem_shmem_test.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)
