virtio: support devices that own their virtqueue memory - #1155
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Let a modern virtio-pci device place its virtqueues and the buffers they reference in a Device Memory Buffer of its own: accept VIRTIO_F_DMB from vp_transport_features(), and implement the get_dmb_shm_id config op on top of vp_modern_get_dmb_shm_id(). get_dmb_shm_id reports the shared memory id of the region that holds the buffer. Take the offer only for a dmb_mem_type of VIRTIO_DMB_MEM_TYPE_COHERENT, the memory type that says a write by either side becomes visible to the other with no cache maintenance by the driver. The driver uses plain loads and stores on the region, so no other type will do. The field is valid from the moment the device offers the feature, so a type the driver does not support leaves the device driven as an ordinary one. The shmid is not readable that early, so a region we fail to locate after the accept fails virtio_features_ok() and probe sets the FAILED status bit. Refuse a device whose common configuration is too short to hold dmb_mem_type, which would put that read outside what vp_modern_probe() mapped. The accept path measures the structure itself, because vp_check_common_size() runs on the features the driver has already accepted and so cannot cover a read that precedes it. Two more things gate the accept. CONFIG_VIRTIO_DMB, so that a device offering the feature to a kernel built without it is driven as an ordinary device. And VIRTIO_F_VERSION_1, because virtio_features_ok() returns early without it, which would leave the feature negotiated and the region never built; this transport refuses such a device anyway. Link: https://lore.kernel.org/virtio-comment/20260818060255.6853-1-graf@amazon.com/ Assisted-by: Kiro:claude-opus-5 checkpatch sparse Signed-off-by: Alexander Graf <graf@amazon.com>
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Pull request for series with
subject: virtio: support devices that own their virtqueue memory
version: 2
url: https://patchwork.kernel.org/project/linux-block/list/?series=1148090