COPY_TRANSFER3D was designed to handle transfers to host. This patch is making it possible to use this CCMD in both directions.
If guest would like to have data from host available immediately, then it should encode CCMD, flush CMD and wait on the guest side.
The data is copied from host to iovec attached to resource. In most cases resource is a staging buffer.
Mesa virgl MR: mesa/mesa!13689 (merged)