On Fri, Aug 12, 2022 at 7:57 AM Rob Clark <robdclark@xxxxxxxxx> wrote: > > 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. The other complication I noticed is that we don't seem to keep around the fd after importing to a GEM handle. And I could imagine that doing so could cause issues with too many fd's. So I guess the best thing is to keep the status quo and let drivers that cannot mmap imported buffers just fail mmap? BR, -R > 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