On Wed, Aug 10, 2022 at 12:26 PM Dmitry Osipenko
<dmitry.osipenko at collabora.com> wrote:>
> On 8/10/22 18:08, Rob Clark wrote:
> > On Wed, Aug 10, 2022 at 4:47 AM Daniel Vetter <daniel at
ffwll.ch> wrote:
> >>
> >> 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 K?nig
<christian.koenig at 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 Hellstr?m
<thomas.hellstrom at linux.intel.com>
> >>>>>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko
at 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.
> >
> > I *think* we'd be ok with this on msm, mostly just by dumb luck.
> > Because the dma-buf's we import will be self-import. I'm less
sure
> > about panfrost (src/panfrost/lib/pan_bo.c doesn't seem to have a
> > special path for imported dma-bufs either, and in that case they
won't
> > be self-imports.. but I guess no one has tried to run android cts on
> > panfrost).
>
> The last time I tried to mmap dma-buf imported to Panfrost didn't work
> because Panfrost didn't implement something needed for that. I'll
need
> to take a look again because can't recall what it was.
>
> > What about something less drastic to start, like (apologies for
> > hand-edited patch):
> >
> > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> > index 86d670c71286..fc9ec42fa0ab 100644
> > --- a/drivers/gpu/drm/drm_gem.c
> > +++ b/drivers/gpu/drm/drm_gem.c
> > @@ -1034,6 +1034,10 @@ int drm_gem_mmap_obj(struct drm_gem_object
> > *obj, unsigned long obj_size,
> > {
> > int ret;
> >
> > + WARN_ON_ONCE(obj->import_attach);
>
> This will hang NVIDIA Tegra, which is what this patch fixed initially.
> If neither of upstream DRM drivers need to map imported dma-bufs and
> never needed, then why do we need this?
oh, tegra isn't using shmem helpers? I assumed it was. Well my point
was to make a more targeted fail on tegra, and a WARN_ON for everyone
else to make it clear that what they are doing is undefined behavior.
Because so far existing userspace (or well, panfrost and freedreno at
least, those are the two I know or checked) don't make special cases
for mmap'ing against the dmabuf fd against the dmabuf fd instead of
the drm device fd.
I *think* it should work out that we don't hit this path with
freedreno but on android I can't really guarantee or prove it. So
your patch would potentially break existing working userspace. Maybe
it is userspace that isn't portable (but OTOH it isn't like you are
going to be using freedreno on tegra). So why don't you go for a more
targeted fix that only returns an error on hw where this is
problematic?
BR,
-R