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. > > > > 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. BR, -R > Regards, > Christian. > > > > > Overall, it still questionable to me whether it's worthwhile to allow > > the mmaping of imported GEMs since only Panfrost/Lima can do it out of > > all drivers and h/w that I tested. Feels like drivers that can do the > > mapping have it just because they can and not because they need. > > >
