On 7/4/22 15:33, Christian König wrote: > Am 30.06.22 um 01:06 schrieb Dmitry Osipenko: >> On 6/29/22 11:43, Thomas Hellström (Intel) wrote: >>> On 6/29/22 10:22, Dmitry Osipenko wrote: >>>> On 6/29/22 09:40, Thomas Hellström (Intel) wrote: >>>>> On 5/27/22 01:50, Dmitry Osipenko wrote: >>>>>> Drivers that use drm_gem_mmap() and drm_gem_mmap_obj() helpers don't >>>>>> handle imported dma-bufs properly, which results in mapping of >>>>>> something >>>>>> else than the imported dma-buf. For example, on NVIDIA Tegra we get a >>>>>> hard >>>>>> lockup when userspace writes to the memory mapping of a dma-buf that >>>>>> was >>>>>> imported into Tegra's DRM GEM. >>>>>> >>>>>> To fix this bug, move mapping of imported dma-bufs to >>>>>> drm_gem_mmap_obj(). >>>>>> Now mmaping of imported dma-bufs works properly for all DRM drivers. >>>>> Same comment about Fixes: as in patch 1, >>>>>> Cc: stable@xxxxxxxxxxxxxxx >>>>>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> >>>>>> --- >>>>>> drivers/gpu/drm/drm_gem.c | 3 +++ >>>>>> drivers/gpu/drm/drm_gem_shmem_helper.c | 9 --------- >>>>>> drivers/gpu/drm/tegra/gem.c | 4 ++++ >>>>>> 3 files changed, 7 insertions(+), 9 deletions(-) >>>>>> >>>>>> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c >>>>>> index 86d670c71286..7c0b025508e4 100644 >>>>>> --- a/drivers/gpu/drm/drm_gem.c >>>>>> +++ b/drivers/gpu/drm/drm_gem.c >>>>>> @@ -1038,6 +1038,9 @@ int drm_gem_mmap_obj(struct drm_gem_object >>>>>> *obj, >>>>>> unsigned long obj_size, >>>>>> if (obj_size < vma->vm_end - vma->vm_start) >>>>>> return -EINVAL; >>>>>> + if (obj->import_attach) >>>>>> + return dma_buf_mmap(obj->dma_buf, vma, 0); >>>>> If we start enabling mmaping of imported dma-bufs on a majority of >>>>> drivers in this way, how do we ensure that user-space is not blindly >>>>> using the object mmap without calling the needed DMA_BUF_IOCTL_SYNC >>>>> which is needed before and after cpu access of mmap'ed dma-bufs? >>>>> >>>>> I was under the impression (admittedly without looking) that the few >>>>> drivers that actually called into dma_buf_mmap() had some private >>>>> user-mode driver code in place that ensured this happened. >>>> Since it's a userspace who does the mapping, then it should be a >>>> responsibility of userspace to do all the necessary syncing. >>> Sure, but nothing prohibits user-space to ignore the syncing thinking >>> "It works anyway", testing those drivers where the syncing is a NOP. And >>> when a driver that finally needs syncing is tested it's too late to fix >>> all broken user-space. >>> >>>> I'm not >>>> sure whether anyone in userspace really needs to map imported dma-bufs >>>> in practice. Nevertheless, this use-case is broken and should be fixed >>>> by either allowing to do the mapping or prohibiting it. >>>> >>> Then I'd vote for prohibiting it, at least for now. And for the future >>> moving forward we could perhaps revisit the dma-buf need for syncing, >>> requiring those drivers that actually need it to implement emulated >>> coherent memory which can be done not too inefficiently (vmwgfx being >>> one example). >> Alright, I'll change it to prohibit the mapping. This indeed should be a >> better option. > > Oh, yes please. But I would expect that some people start screaming. > > Over time I've got tons of TTM patches because people illegally tried to > mmap() imported DMA-bufs in their driver. > > Anyway this is probably the right thing to do and we can work on fixing > the fallout later on. I already sent out the patch [1] that prohibits the mapping. Would be great if you all could take a look and give a r-b, thanks in advance. [1] https://patchwork.freedesktop.org/patch/492148/ -- Best regards, Dmitry
