vdpasim: vDPA device simulator

This patch implements a software vDPA networking device. The datapath
is implemented through vringh and workqueue. The device has an on-chip
IOMMU which translates IOVA to PA. For kernel virtio drivers, vDPA
simulator driver provides dma_ops. For vhost driers, set_map() methods
of vdpa_config_ops is implemented to accept mappings from vhost.

A sysfs based management interface is implemented, devices are
created and removed through:

/sys/devices/virtual/vdpa_simulator/netdev/{create|remove}

Netlink based lifecycle management could be implemented for vDPA
simulator as well.

Currently, vDPA device simulator will loopback TX traffic to RX. So
the main use case for the device is vDPA feature testing, prototyping
and development.

Signed-off-by: Jason Wang <jasowang@redhat.com>

drivers/virtio/vdpa/Kconfig

@@ -7,3 +7,20 @@ config VDPA
           datapath which complies with virtio specifications with
           vendor specific control path.
 
+menuconfig VDPA_MENU
+	bool "VDPA drivers"
+	default n
+
+if VDPA_MENU
+
+config VDPA_SIM
+	tristate "vDPA device simulator"
+        select VDPA
+        default n
+        help
+          vDPA networking device simulator which loop TX traffic back
+          to RX. This device is used for testing, prototyping and
+          development of vDPA.
+
+endif # VDPA_MENU
+

drivers/virtio/vdpa/Makefile

@@ -1,2 +1,3 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_VDPA) += vdpa.o
+obj-$(CONFIG_VDPA_SIM) += vdpa_sim.o