Re: [PATCH v2] drm/tests: shmem: Set DMA mask to 64-bit in drm_gem_shmem

[Thomas Zimmermann <tzimmermann@suse.de>]

Am 03.07.26 um 16:27 schrieb José Expósito:
> From: José Expósito <jose.exposito@redhat.com>
>
> drm_gem_shmem_test_purge [1] and drm_gem_shmem_test_get_pages_sgt [2]
> intermittently fail on ppc64le and s390x CI systems with a DMA address
> overflow:
>
>    DMA addr 0x0000000100307000+4096 overflow (mask ffffffff, bus limit 0)
>    WARNING: kernel/dma/direct.h:114 dma_direct_map_sg+0x778/0x920
>
>    drm_gem_shmem_test_purge: ASSERTION FAILED at
>      drivers/gpu/drm/tests/drm_gem_shmem_test.c:330
>      Expected sgt is not error, but is: -5
>
> The call chain leading to the failure is:
>
>    drm_gem_shmem_test_purge() / drm_gem_shmem_test_get_pages_sgt()
>      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
>
> The root cause is that KUnit devices are initialized with a 32-bit DMA
> mask (DMA_BIT_MASK(32)) in lib/kunit/device.c. On ppc64le and s390x
> systems with physical memory above 4GB, page allocations can land at
> addresses that exceed this mask. When drm_gem_shmem_get_pages_sgt()
> attempts to DMA-map these pages via dma_map_sgtable(), the DMA layer
> rejects the mapping because the physical address overflows the 32-bit
> mask.
>
> The failure is intermittent because pages may or may not be allocated
> above 4GB on any given run depend on memory pressure.
>
> Fix by setting a 64-bit DMA mask on the device before calling
> drm_gem_shmem_get_pages_sgt() for all tests, following the same pattern
> already used in drm_gem_shmem_test_obj_create_private().
>
> [1] https://s3.amazonaws.com/arr-cki-prod-trusted-artifacts/trusted-artifacts/2643976103/test_s390x/15128551935/artifacts/jobwatch/logs/recipes/21561049/tasks/220716793/results/1014626315/logs/dmesg.log
> [2] https://s3.amazonaws.com/arr-cki-prod-trusted-artifacts/trusted-artifacts/2643976103/test_ppc64le/15128551933/artifacts/jobwatch/logs/recipes/21561041/tasks/220716705/results/1014628163/logs/dmesg.log
>
> Fixes: 93032ae634d4 ("drm/test: add a test suite for GEM objects backed by shmem")
> Closes: https://datawarehouse.cki-project.org/issue/5345
> Closes: https://datawarehouse.cki-project.org/issue/3184
> Assisted-by: Claude:claude-4.6-opus
> Signed-off-by: José Expósito <jose.exposito@redhat.com>
>
> ---
>
> v2:
>
>    - Move fix to drm_gem_shmem_test_init() (Thomas Zimmermann)
>    - Link to v1: https://lore.kernel.org/dri-devel/20260703063517.6346-1-jose.exposito89@gmail.com/
> ---
>   drivers/gpu/drm/tests/drm_gem_shmem_test.c | 17 +++++++++--------
>   1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/tests/drm_gem_shmem_test.c b/drivers/gpu/drm/tests/drm_gem_shmem_test.c
> index 44a190109249..6e6b4f4902c2 100644
> --- a/drivers/gpu/drm/tests/drm_gem_shmem_test.c
> +++ b/drivers/gpu/drm/tests/drm_gem_shmem_test.c
> @@ -94,14 +94,6 @@ static void drm_gem_shmem_test_obj_create_private(struct kunit *test)
>   
>   	sg_init_one(sgt->sgl, buf, TEST_SIZE);
>   
> -	/*
> -	 * Set the DMA mask to 64-bits and map the sgtables
> -	 * otherwise drm_gem_shmem_free will cause a warning
> -	 * on debug kernels.
> -	 */
> -	ret = dma_set_mask(drm_dev->dev, DMA_BIT_MASK(64));
> -	KUNIT_ASSERT_EQ(test, ret, 0);
> -
>   	ret = dma_map_sgtable(drm_dev->dev, sgt, DMA_BIDIRECTIONAL, 0);
>   	KUNIT_ASSERT_EQ(test, ret, 0);
>   
> @@ -352,11 +344,20 @@ static int drm_gem_shmem_test_init(struct kunit *test)
>   {
>   	struct device *dev;
>   	struct drm_device *drm_dev;
> +	int ret;
>   
>   	/* Allocate a parent device */
>   	dev = drm_kunit_helper_alloc_device(test);
>   	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, dev);
>   
> +	/*
> +	 * Set the DMA mask to 64-bits and map the sgtables
> +	 * otherwise drm_gem_shmem_free will cause a warning
> +	 * on debug kernels.
> +	 */
> +	ret = dma_set_mask(dev, DMA_BIT_MASK(64));
> +	KUNIT_ASSERT_EQ(test, ret, 0);
> +

The comment sounds a bit off, but still

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>

>   	/*
>   	 * The DRM core will automatically initialize the GEM core and create
>   	 * a DRM Memory Manager object which provides an address space pool

-- 
--
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)