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. >> >>> 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. > 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. -- Best regards, Dmitry