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. Alright, let's keep the dma-buf mapping as-is for now. I'll fix just the Tegra driver then. -- Best regards, Dmitry