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. 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) > >
