KVM: api: Pass the devid in the msi routing entry

On ARM, the MSI msg (address and data) comes along with
out-of-band device ID information. The device ID encodes the
device that writes the MSI msg. Let's convey the device id in
kvm_irq_routing_msi and use KVM_MSI_VALID_DEVID flag value in
kvm_irq_routing_entry to indicate the msi devid is populated.
Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

Documentation/virtual/kvm/api.txt

@@ -1468,7 +1468,11 @@ struct kvm_irq_routing_entry {
 #define KVM_IRQ_ROUTING_S390_ADAPTER 3
 #define KVM_IRQ_ROUTING_HV_SINT 4
 
-No flags are specified so far, the corresponding field must be set to zero.
+flags:
+- KVM_MSI_VALID_DEVID: used along with KVM_IRQ_ROUTING_MSI
+  routing entry type, specifies that the devid field contains
+  a valid value.
+- zero otherwise
 
 struct kvm_irq_routing_irqchip {
 	__u32 irqchip;
@@ -1479,9 +1483,20 @@ struct kvm_irq_routing_msi {
 	__u32 address_lo;
 	__u32 address_hi;
 	__u32 data;
+	union {
 		__u32 pad;
+		__u32 devid;
+	};
 };
 
+devid: If KVM_MSI_VALID_DEVID is set, contains a unique device identifier
+       for the device that wrote the MSI message.
+       For PCI, this is usually a BFD identifier in the lower 16 bits.
+
+The per-VM KVM_CAP_MSI_DEVID capability advertises the requirement to
+provide the device ID. If this capability is not set, userland cannot
+rely on the kernel to allow the KVM_MSI_VALID_DEVID flag being set.
+
 struct kvm_irq_routing_s390_adapter {
 	__u64 ind_addr;
 	__u64 summary_addr;

include/uapi/linux/kvm.h

@@ -879,7 +879,10 @@ struct kvm_irq_routing_msi {
 	__u32 address_lo;
 	__u32 address_hi;
 	__u32 data;
+	union {
 		__u32 pad;
+		__u32 devid;
+	};
 };
 
 struct kvm_irq_routing_s390_adapter {