vhost: introduce vDPA-based backend

This patch introduces a vDPA-based vhost backend. This backend is
built on top of the same interface defined in virtio-vDPA and provides
a generic vhost interface for userspace to accelerate the virtio
devices in guest.

This backend is implemented as a vDPA device driver on top of the same
ops used in virtio-vDPA. It will create char device entry named
vhost-vdpa-$index for userspace to use. Userspace can use vhost ioctls
on top of this char device to setup the backend.

Vhost ioctls are extended to make it type agnostic and behave like a
virtio device, this help to eliminate type specific API like what
vhost_net/scsi/vsock did:

- VHOST_VDPA_GET_DEVICE_ID: get the virtio device ID which is defined
  by virtio specification to differ from different type of devices
- VHOST_VDPA_GET_VRING_NUM: get the maximum size of virtqueue
  supported by the vDPA device
- VHSOT_VDPA_SET/GET_STATUS: set and get virtio status of vDPA device
- VHOST_VDPA_SET/GET_CONFIG: access virtio config space
- VHOST_VDPA_SET_VRING_ENABLE: enable a specific virtqueue

For memory mapping, IOTLB API is mandated for vhost-vDPA which means
userspace drivers are required to use
VHOST_IOTLB_UPDATE/VHOST_IOTLB_INVALIDATE to add or remove mapping for
a specific userspace memory region.

The vhost-vDPA API is designed to be type agnostic, but it allows net
device only in current stage. Due to the lacking of control virtqueue
support, some features were filter out by vhost-vdpa.

We will enable more features and devices in the near future.
Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20200326140125.19794-8-jasowang@redhat.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vhost/Kconfig

@@ -59,6 +59,18 @@ config VHOST_VSOCK
 	To compile this driver as a module, choose M here: the module will be called
 	vhost_vsock.
 
+config VHOST_VDPA
+	tristate "Vhost driver for vDPA-based backend"
+	depends on EVENTFD
+	select VHOST
+	select VDPA
+	help
+	  This kernel module can be loaded in host kernel to accelerate
+	  guest virtio devices with the vDPA-based backends.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called vhost_vdpa.
+
 config VHOST_CROSS_ENDIAN_LEGACY
 	bool "Cross-endian support for vhost"
 	default n

drivers/vhost/Makefile

@@ -10,6 +10,9 @@ vhost_vsock-y := vsock.o
 
 obj-$(CONFIG_VHOST_RING) += vringh.o
 
+obj-$(CONFIG_VHOST_VDPA) += vhost_vdpa.o
+vhost_vdpa-y := vdpa.o
+
 obj-$(CONFIG_VHOST)	+= vhost.o
 
 obj-$(CONFIG_VHOST_IOTLB) += vhost_iotlb.o

include/uapi/linux/vhost.h

@@ -116,4 +116,28 @@
 #define VHOST_VSOCK_SET_GUEST_CID	_IOW(VHOST_VIRTIO, 0x60, __u64)
 #define VHOST_VSOCK_SET_RUNNING		_IOW(VHOST_VIRTIO, 0x61, int)
 
+/* VHOST_VDPA specific defines */
+
+/* Get the device id. The device ids follow the same definition of
+ * the device id defined in virtio-spec.
+ */
+#define VHOST_VDPA_GET_DEVICE_ID	_IOR(VHOST_VIRTIO, 0x70, __u32)
+/* Get and set the status. The status bits follow the same definition
+ * of the device status defined in virtio-spec.
+ */
+#define VHOST_VDPA_GET_STATUS		_IOR(VHOST_VIRTIO, 0x71, __u8)
+#define VHOST_VDPA_SET_STATUS		_IOW(VHOST_VIRTIO, 0x72, __u8)
+/* Get and set the device config. The device config follows the same
+ * definition of the device config defined in virtio-spec.
+ */
+#define VHOST_VDPA_GET_CONFIG		_IOR(VHOST_VIRTIO, 0x73, \
+					     struct vhost_vdpa_config)
+#define VHOST_VDPA_SET_CONFIG		_IOW(VHOST_VIRTIO, 0x74, \
+					     struct vhost_vdpa_config)
+/* Enable/disable the ring. */
+#define VHOST_VDPA_SET_VRING_ENABLE	_IOW(VHOST_VIRTIO, 0x75, \
+					     struct vhost_vring_state)
+/* Get the max ring size. */
+#define VHOST_VDPA_GET_VRING_NUM	_IOR(VHOST_VIRTIO, 0x76, __u16)
+
 #endif

include/uapi/linux/vhost_types.h

@@ -119,6 +119,14 @@ struct vhost_scsi_target {
 	unsigned short reserved;
 };
 
+/* VHOST_VDPA specific definitions */
+
+struct vhost_vdpa_config {
+	__u32 off;
+	__u32 len;
+	__u8 buf[0];
+};
+
 /* Feature bits */
 /* Log all write descriptors. Can be changed while device is active. */
 #define VHOST_F_LOG_ALL 26