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. 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. -- Best regards, Dmitry
