Re: [PATCH v7 2/2] drm/gem: Don't map imported GEMs

[Dmitry Osipenko]

Hello Thomas,

On 6/30/22 23:15, Thomas Hellström (Intel) wrote:
> Hi, Dmitry,
> 
> On 6/30/22 22:04, 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. 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.
>>
>> Majority of DRM drivers prohibit mapping of the imported GEM objects.
>> Mapping of imported GEMs require special care from userspace since it
>> should sync dma-buf because mapping coherency of the exporter device may
>> not match the DRM device. Let's prohibit the mapping for all DRM drivers
>> for consistency.
>>
>> Cc: stable@xxxxxxxxxxxxxxx
>> Suggested-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
> 
> This might break drivers whose obj->funcs->mmap() callback already
> handles this case, and has userspace that does the right thing.

The drm-shmem helper should be the only that maps imported GEMs
properly, but drivers that use drm-shmem already prohibit to map
imported GEMs. Okay, I'll try to re-check once again to be sure.

> I think the disabling must be checked on a per-driver basis to avoid
> that; in particular drivers that already call dma_buf_mmap() should be
> able to continue doing this.
> 
> Also the Fixes: review comment remains,

This should've been broken forever, don't think that we have a fixes tag
here. I looked thought all my previous patches and added the Fixes
wherever was possible. If I really missed something, then please let me
know.

-- 
Best regards,
Dmitry