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Fri, 03 Jul 2026 07:30:13 -0700 (PDT) Date: Fri, 3 Jul 2026 16:30:12 +0200 From: =?iso-8859-1?Q?Jos=E9_Exp=F3sito?= To: Thomas Zimmermann Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, maarten.lankhorst@linux.intel.com, mripard@kernel.org, airlied@gmail.com, simona@ffwll.ch, boris.brezillon@collabora.com, kees@kernel.org Subject: Re: [PATCH 0/2] drm/tests: shmem: Fix intermittent DMA overflow on ppc64le/s390x Message-ID: References: <20260703063517.6346-1-jose.exposito89@gmail.com> <285af006-f403-4c3d-8cd6-e0318c188b85@suse.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <285af006-f403-4c3d-8cd6-e0318c188b85@suse.de> On Fri, Jul 03, 2026 at 12:32:18PM +0200, Thomas Zimmermann wrote: > 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. I just sent v2 with the suggested change. I run the test in several architectures and I didn't run into any issue: https://lore.kernel.org/dri-devel/20260703142749.4099-1-jose.exposito89@gmail.com/ Thanks, Jose > > 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) > >