Hi Dmitry, > Subject: Re: [PATCH v5 0/5] drm/virtio: Import scanout buffers from other > devices > > Hello, Vivek > > All patches applied to misc-next with a small modification, thanks! Thank you so much for taking the time to test, review and merge this series!! > > Note: While verifying move_notify(), I noticed that AMD/TTM driver moves > same shared FB GEMs after each framebuffer update when it renders into > FB, despite of the 32GB BAR. This should be rather inefficient. I'd > expect dma-buf staying static if there is no need to evict it. Something > to check how it works with DG2. IIUC, I think the exporting driver (AMD GPU driver) in the Guest VM migrates the FB to System RAM because during export it determines that virtio-gpu is not P2P compatible. This behavior is expected and seen with other dGPU drivers (i915/Xe) as well. However, I am trying to fix this in Xe driver for specific use-cases (SRIOV) where we know for sure that the importer on the Host is another dGPU: https://patchwork.kernel.org/project/dri-devel/cover/20241012024524.1377836-1-vivek.kasireddy@xxxxxxxxx/ https://patchwork.kernel.org/project/dri-devel/cover/20240624065552.1572580-1-vivek.kasireddy@xxxxxxxxx/ > > Fix: I made this change to the "Import prime buffers" patch after > spotting possibility of having race condition between move_notify() and > freeing GEM: This fix LGTM. Thanks, Vivek > > diff --git a/drivers/gpu/drm/virtio/virtgpu_prime.c > b/drivers/gpu/drm/virtio/virtgpu_prime.c > index 8644b87d473d..688810d1b611 100644 > --- a/drivers/gpu/drm/virtio/virtgpu_prime.c > +++ b/drivers/gpu/drm/virtio/virtgpu_prime.c > @@ -189,13 +189,18 @@ static void virtgpu_dma_buf_free_obj(struct > drm_gem_object *obj) > struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj); > struct virtio_gpu_device *vgdev = obj->dev->dev_private; > struct dma_buf_attachment *attach = obj->import_attach; > + struct dma_resv *resv = attach->dmabuf->resv; > > if (attach) { > + dma_resv_lock(resv, NULL); > + > virtio_gpu_detach_object_fenced(bo); > > if (bo->sgt) > - dma_buf_unmap_attachment_unlocked(attach, bo- > >sgt, > - > DMA_BIDIRECTIONAL); > + dma_buf_unmap_attachment(attach, bo->sgt, > + DMA_BIDIRECTIONAL); > + > + dma_resv_unlock(resv); > > dma_buf_detach(attach->dmabuf, attach); > dma_buf_put(attach->dmabuf); > @@ -268,7 +273,7 @@ static void virtgpu_dma_buf_move_notify(struct > dma_buf_attachment *attach) > struct drm_gem_object *obj = attach->importer_priv; > struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj); > > - if (bo->created) { > + if (bo->created && kref_read(&obj->refcount)) { > virtio_gpu_detach_object_fenced(bo); > > if (bo->sgt) > > > -- > Best regards, > Dmitry
