On Mon, Jun 8, 2020 at 6:43 PM Michael S. Tsirkin [off-list ref] wrote:

On Fri, May 15, 2020 at 04:26:15PM +0900, David Stevens wrote:

quoted

quoted

quoted

+     if (virtio_has_feature(vgdev->vdev, VIRTIO_GPU_F_RESOURCE_UUID)) {
+             vgdev->has_resource_assign_uuid = true;
+     }

Just a question: this relies on DMA bufs so I assume it is
not really assumed to work when DMA API is bypassed, right?
Rather than worry what does it mean, how about just
disabling  this feature without PLATFORM_DMA for now?

By PLATFORM_DMA, do you mean CONFIG_DMA_SHARED_BUFFER?

Sorry, no. I mean VIRTIO_F_IOMMU_PLATFORM which in the
future will be renamed to VIRTIO_F_PLATFORM_ACCESS.

Shouldn't things work independent of whether or not that feature is
set? If a virtio driver properly uses the dma_buf APIs (which virtgpu
seems to), then that should take care of any mapping/synchronization
related to VIRTIO_F_IOMMU_PLATFORM. If anything, the case where
VIRTIO_F_IOMMU_PLATFORM isn't set is easier, since then we know that
the "the device has same access [sic] to memory addresses supplied to
it as the driver has", according to the specification.

-David