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. -- Best regards, Dmitry
