um: Add VFIO-based virtual PCI driver

Implement a new virtual PCI driver based on the VFIO framework.
This driver allows users to pass through PCI devices to UML via
VFIO. Currently, only MSI-X capable devices are supported, and
it is assumed that drivers will use MSI-X.

Signed-off-by: Tiwei Bie <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Johannes Berg <[email protected]>

Author: btw616

arch/um/drivers/Kconfig

@@ -367,3 +367,11 @@ config UML_PCI_OVER_VIRTIO_DEVICE_ID
 	  There's no official device ID assigned (yet), set the one you
 	  wish to use for experimentation here. The default of -1 is
 	  not valid and will cause the driver to fail at probe.
+
+config UML_PCI_OVER_VFIO
+	bool "Enable VFIO-based PCI passthrough"
+	select UML_PCI
+	help
+	  This driver provides support for VFIO-based PCI passthrough.
+	  Currently, only MSI-X capable devices are supported, and it
+	  is assumed that drivers will use MSI-X.

arch/um/drivers/Makefile

@@ -19,6 +19,7 @@ port-objs := port_kern.o port_user.o
 harddog-objs := harddog_kern.o
 harddog-builtin-$(CONFIG_UML_WATCHDOG) := harddog_user.o harddog_user_exp.o
 rtc-objs := rtc_kern.o rtc_user.o
+vfio_uml-objs := vfio_kern.o vfio_user.o
 
 LDFLAGS_vde.o = $(shell $(CC) $(CFLAGS) -print-file-name=libvdeplug.a)
 
@@ -62,6 +63,7 @@ obj-$(CONFIG_VIRTIO_UML) += virtio_uml.o
 obj-$(CONFIG_UML_RTC) += rtc.o
 obj-$(CONFIG_UML_PCI) += virt-pci.o
 obj-$(CONFIG_UML_PCI_OVER_VIRTIO) += virtio_pcidev.o
+obj-$(CONFIG_UML_PCI_OVER_VFIO) += vfio_uml.o
 
 # pcap_user.o must be added explicitly.
 USER_OBJS := fd.o null.o pty.o tty.o xterm.o slip_common.o vde_user.o vector_user.o