On Fri, Aug 12, 2022 at 4:26 AM Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> wrote: > > On 8/11/22 02:19, Rob Clark wrote: > > On Wed, Aug 10, 2022 at 3:23 PM Dmitry Osipenko > > <dmitry.osipenko@xxxxxxxxxxxxx> wrote: > >> > >> On 8/11/22 01:03, Rob Clark wrote: > >>> On Wed, Aug 10, 2022 at 12:26 PM Dmitry Osipenko > >>> <dmitry.osipenko@xxxxxxxxxxxxx> wrote: > >>>> > >>>> On 8/10/22 18:08, Rob Clark wrote: > >>>>> On Wed, Aug 10, 2022 at 4:47 AM Daniel Vetter <daniel@xxxxxxxx> 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 König <christian.koenig@xxxxxxx> 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@xxxxxxxxxxxxxxx> > >>>>>>>>>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> > >>>>>>>>> > >>>>>>>>> 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. > Upd: I re-checked Panfrost using today's linux-next and mapping of > imported dma-buf works, I mapped imported buf from video decoder. > Apparently previously I had some local kernel change that broke the mapping. > > >>>>> 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. > >> > >> It's not clear to me what bad Android does form yours comments. Does it > >> export dma-buf from GPU and then import it to GPU? If yes, then DRM core > >> has a check for the self-importing [1]. > >> > >> [1] > >> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_prime.c#L918 > >> > >> If you're meaning something else, then please explain in a more details. > > > > So, android/gralloc allocates buffers externally to the driver and > > imports them into driver. (And that seems to not just be window > > surfaces, but in cases random textures, etc) > > > > In the normal case these should be allocated from drm/msm so it should > > hit [1].. this is the "dumb luck" I mentioned earlier. But I'm not > > confident enough to say that there is no other case. > > > >> > >>> 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? > >> > >> That's what the first versions of the patch did and Christian suggested > >> that it's not a good approach. In fact it should be not only Tegra that > >> has a broken dma-buf mapping, but apparently OMAP driver too. > > > > Hmm, I guess I'm a bit more conservative when it comes to potentially > > breaking userspace. > > If such userspace exists, then of course the mapping should continue to > work. Still will be great to know what that userpsace is. Definitely existing mesa does not have a special mmap path for imported dma-bufs (both in the case of panfrost and freedreno, I didn't check any others). The only question is whether there is a case where some app/test/etc imports a foreign dma-buf fd and then does something that would trigger mmap'ing, like readpix. BR, -R > Alright, let's keep the dma-buf mapping as-is for now. I'll fix just the > Tegra driver then. > > -- > Best regards, > Dmitry