On 6/29/22 11:43, Thomas Hellström (Intel) wrote:
On 6/29/22 10:22, Dmitry Osipenko wrote:Alright, I'll change it to prohibit the mapping. This indeed should be a
On 6/29/22 09:40, Thomas Hellström (Intel) wrote:Sure, but nothing prohibits user-space to ignore the syncing thinking
On 5/27/22 01:50, Dmitry Osipenko wrote:Since it's a userspace who does the mapping, then it should be a
Drivers that use drm_gem_mmap() and drm_gem_mmap_obj() helpers don'tSame comment about Fixes: as in patch 1,
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.
Cc: stable@xxxxxxxxxxxxxxxIf we start enabling mmaping of imported dma-bufs on a majority of
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);
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.
responsibility of userspace to do all the necessary syncing.
"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 notThen I'd vote for prohibiting it, at least for now. And for the future
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.
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).
better option.