virtio: introduce map ops in virtio core

This patch introduces map operations for virtio device. Virtio used to
use DMA API which is not necessarily the case since some devices
doesn't do DMA. Instead of using tricks and abusing DMA API, let's
simply abstract the current mapping logic into a virtio specific
mapping operations. For the device or transport that doesn't do DMA,
they can implement their own mapping logic without the need to trick
DMA core. In this case the mapping metadata is opaque to the virtio
core that will be passed back to the transport or device specific map
operations. For other devices, DMA API will still be used, so map
token will still be the dma device to minimize the changeset and
performance impact.

The mapping operations are abstracted as a independent structure
instead of reusing virtio_config_ops. This allows the transport can
simply reuse the structure for lower layers like vDPA.

A set of new mapping helpers were introduced for the device that want
to do mapping by themselves.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20250821064641.5025-7-jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>
Reviewed-by: Eugenio Pérez <eperezma@redhat.com>

1 files changed, 72 insertions, 0 deletions

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 7427b79d6f3d..16001e9f9b39 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -139,6 +139,78 @@ struct virtio_config_ops {
 	int (*enable_vq_after_reset)(struct virtqueue *vq);
 };
 
+/**
+ * struct virtio_map_ops - operations for mapping buffer for a virtio device
+ * Note: For transport that has its own mapping logic it must
+ * implements all of the operations
+ * @map_page: map a buffer to the device
+ *      map: metadata for performing mapping
+ *      page: the page that will be mapped by the device
+ *      offset: the offset in the page for a buffer
+ *      size: the buffer size
+ *      dir: mapping direction
+ *      attrs: mapping attributes
+ *      Returns: the mapped address
+ * @unmap_page: unmap a buffer from the device
+ *      map: device specific mapping map
+ *      map_handle: the mapped address
+ *      size: the buffer size
+ *      dir: mapping direction
+ *      attrs: unmapping attributes
+ * @sync_single_for_cpu: sync a single buffer from device to cpu
+ *      map: metadata for performing mapping
+ *      map_handle: the mapping address to sync
+ *      size: the size of the buffer
+ *      dir: synchronization direction
+ * @sync_single_for_device: sync a single buffer from cpu to device
+ *      map: metadata for performing mapping
+ *      map_handle: the mapping address to sync
+ *      size: the size of the buffer
+ *      dir: synchronization direction
+ * @alloc: alloc a coherent buffer mapping
+ *      map: metadata for performing mapping
+ *      size: the size of the buffer
+ *      map_handle: the mapping address to sync
+ *      gfp: allocation flag (GFP_XXX)
+ *      Returns: virtual address of the allocated buffer
+ * @free: free a coherent buffer mapping
+ *      map: metadata for performing mapping
+ *      size: the size of the buffer
+ *      vaddr: virtual address of the buffer
+ *      map_handle: the mapping address to sync
+ *      attrs: unmapping attributes
+ * @need_sync: if the buffer needs synchronization
+ *      map: metadata for performing mapping
+ *      map_handle: the mapped address
+ *      Returns: whether the buffer needs synchronization
+ * @mapping_error: if the mapping address is error
+ *      map: metadata for performing mapping
+ *      map_handle: the mapped address
+ * @max_mapping_size: get the maximum buffer size that can be mapped
+ *      map: metadata for performing mapping
+ *      Returns: the maximum buffer size that can be mapped
+ */
+struct virtio_map_ops {
+	dma_addr_t (*map_page)(union virtio_map map, struct page *page,
+			       unsigned long offset, size_t size,
+			       enum dma_data_direction dir, unsigned long attrs);
+	void (*unmap_page)(union virtio_map map, dma_addr_t map_handle,
+			   size_t size, enum dma_data_direction dir,
+			   unsigned long attrs);
+	void (*sync_single_for_cpu)(union virtio_map map, dma_addr_t map_handle,
+				    size_t size, enum dma_data_direction dir);
+	void (*sync_single_for_device)(union virtio_map map,
+				       dma_addr_t map_handle, size_t size,
+				       enum dma_data_direction dir);
+	void *(*alloc)(union virtio_map map, size_t size,
+		       dma_addr_t *map_handle, gfp_t gfp);
+	void (*free)(union virtio_map map, size_t size, void *vaddr,
+		     dma_addr_t map_handle, unsigned long attrs);
+	bool (*need_sync)(union virtio_map map, dma_addr_t map_handle);
+	int (*mapping_error)(union virtio_map map, dma_addr_t map_handle);
+	size_t (*max_mapping_size)(union virtio_map map);
+};
+
 /* If driver didn't advertise the feature, it will never appear. */
 void virtio_check_driver_offered_feature(const struct virtio_device *vdev,
 					 unsigned int fbit);