On 8/23/22 19:47, Rob Clark wrote: > On Tue, Aug 23, 2022 at 3:01 AM Christian König > <ckoenig.leichtzumerken@xxxxxxxxx> wrote: >> >> Am 22.08.22 um 19:26 schrieb Dmitry Osipenko: >>> On 8/16/22 22:55, Dmitry Osipenko wrote: >>>> On 8/16/22 15:03, Christian König wrote: >>>>> Am 16.08.22 um 13:44 schrieb Dmitry Osipenko: >>>>>> [SNIP] >>>>>>> The other complication I noticed is that we don't seem to keep around >>>>>>> the fd after importing to a GEM handle. And I could imagine that >>>>>>> doing so could cause issues with too many fd's. So I guess the best >>>>>>> thing is to keep the status quo and let drivers that cannot mmap >>>>>>> imported buffers just fail mmap? >>>>>> That actually should be all the drivers excluding those that use >>>>>> DRM-SHMEM because only DRM-SHMEM uses dma_buf_mmap(), that's why it >>>>>> works for Panfrost. I'm pretty sure mmaping of imported GEMs doesn't >>>>>> work for the MSM driver, isn't it? >>>>>> >>>>>> Intel and AMD drivers don't allow to map the imported dma-bufs. Both >>>>>> refuse to do the mapping. >>>>>> >>>>>> Although, AMDGPU "succeeds" to do the mapping using >>>>>> AMDGPU_GEM_DOMAIN_GTT, but then touching the mapping causes bus fault, >>>>>> hence mapping actually fails. I think it might be the AMDGPU >>>>>> driver/libdrm bug, haven't checked yet. >>>>> That's then certainly broken somehow. Amdgpu should nerve ever have >>>>> allowed to mmap() imported DMA-bufs and the last time I check it didn't. >>>> I'll take a closer look. So far I can only tell that it's a kernel >>>> driver issue because once I re-applied this "Don't map imported GEMs" >>>> patch, AMDGPU began to refuse mapping AMDGPU_GEM_DOMAIN_GTT. >>>> >>>>>> So we're back to the point that neither of DRM drivers need to map >>>>>> imported dma-bufs and this was never tested. In this case this patch is >>>>>> valid, IMO. >>>> Actually, I'm now looking at Etnaviv and Nouveau and seems they should >>>> map imported dma-buf properly. I know that people ran Android on >>>> Etnaviv. So maybe devices with a separated GPU/display need to map >>>> imported display BO for Android support. Wish somebody who ran Android >>>> on one of these devices using upstream drivers could give a definitive >>>> answer. I may try to test Nouveau later on. >>>> >>> Nouveau+Intel combo doesn't work because of [1] that says: >>> >>> "Refuse to fault imported pages. This should be handled (if at all) by >>> redirecting mmap to the exporter." >>> >>> [1] >>> https://elixir.bootlin.com/linux/v5.19/source/drivers/gpu/drm/ttm/ttm_bo_vm.c#L154 >>> >>> Interestingly, I noticed that there are IGT tests which check prime >>> mmaping of Nouveau+Intel [2] (added 9 years ago), but they fail as well, >>> as expected. The fact that IGT has such tests is interesting because it >>> suggests that the mapping worked in the past. It's also surprising that >>> nobody cared to fix the failing tests. For the reference, I checked >>> v5.18 and today's linux-next. >>> >>> [2] >>> https://gitlab.freedesktop.org/drm/igt-gpu-tools/-/blob/master/tests/prime_nv_test.c#L132 >>> >>> Starting subtest: nv_write_i915_cpu_mmap_read >>> Received signal SIGBUS. >>> Stack trace: >>> #0 [fatal_sig_handler+0x163] >>> #1 [__sigaction+0x50] >>> #2 [__igt_unique____real_main354+0x406] >>> #3 [main+0x23] >>> #4 [__libc_start_call_main+0x80] >>> #5 [__libc_start_main+0x89] >>> #6 [_start+0x25] >>> Subtest nv_write_i915_cpu_mmap_read: CRASH (0,005s) >>> >>> Starting subtest: nv_write_i915_gtt_mmap_read >>> Received signal SIGBUS. >>> Stack trace: >>> #0 [fatal_sig_handler+0x163] >>> #1 [__sigaction+0x50] >>> #2 [__igt_unique____real_main354+0x33d] >>> #3 [main+0x23] >>> #4 [__libc_start_call_main+0x80] >>> #5 [__libc_start_main+0x89] >>> #6 [_start+0x25] >>> Subtest nv_write_i915_gtt_mmap_read: CRASH (0,004s) >>> >>> I'm curious about the Etnaviv driver because it uses own shmem >>> implementation and maybe it has a working mmaping of imported GEMs since >>> it imports the dma-buf pages into Entaviv BO. Although, it should be >>> risking to map pages using a different caching attributes (WC) from the >>> exporter, which is prohibited on ARM ad then one may try to map imported >>> udmabuf. I see now that Etnaviv uses dma_buf_mmap(), so it should be okay. >>> Apparently, the Intel DG TTM driver should be able to map imported >>> dma-buf because it sets TTM_TT_FLAG_EXTERNAL_MAPPABLE. >> >> Even with that flag set it is illegal to map the pages directly by an >> importer. >> >> If that ever worked then the only real solution is to redirect mmap() >> calls on importer BOs to dma_buf_mmap(). > > Yeah, I think this is the best option. Forcing userspace to hang on > to the fd just in case someone calls readpix would be pretty harsh. Actually, I proposed this couple months ago [1]. [1] https://patchwork.freedesktop.org/patch/487481/ What's not clear to me is how userspace is supposed to sync CPU accesses for imported GEMs. Either userspace need to use dma_buf_sync UAPI for dmabuf of imported GEM or importer driver should do that, or there is some other option? -- Best regards, Dmitry
