Re: [PATCH v8 2/2] drm/gem: Don't map imported GEMs

Daniel Vetter
2022-08-10T11:47:20Z

On Wed, Jul 06, 2022 at 10:02:07AM +0300, Dmitry Osipenko wrote:
> On 7/6/22 00:48, Rob Clark wrote:
> > On Tue, Jul 5, 2022 at 4:51 AM Christian König <christian.koenig@amd.com> wrote:
> >>
> >> Am 01.07.22 um 11:02 schrieb Dmitry Osipenko:
> >>> 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.
> >>>
> >>> Suggested-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> >>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> >>
> >> I'm pretty sure that this is the right approach, but it's certainly more
> >> than possible that somebody abused this already.
> >
> > I suspect that this is abused if you run deqp cts on android.. ie. all
> > winsys buffers are dma-buf imports from gralloc. And then when you
> > hit readpix...
> >
> > You might only hit this in scenarios with separate gpu and display (or
> > dGPU+iGPU) because self-imports are handled differently in
> > drm_gem_prime_import_dev().. and maybe not in cases where you end up
> > with a blit from tiled/compressed to linear.. maybe that narrows the
> > scope enough to just fix it in userspace?
>
> Given that that only drivers which use DRM-SHMEM potentially could've
> map imported dma-bufs (Panfrost, Lima) and they already don't allow to
> do that, I think we're good.

So can I have an ack from Rob here or are there still questions that this
might go boom?

Dmitry, since you have a bunch of patches merged now I think would also be
good to get commit rights so you can drive this more yourself. I've asked
Daniel Stone to help you out with getting that.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation