[RFC v2 5/9] KVM: KVM-VFIO: update user API to program forwarded IRQ

[Eric Auger]

add new device group commands:
- KVM_DEV_VFIO_DEVICE_FORWARD_IRQ and
  KVM_DEV_VFIO_DEVICE_UNFORWARD_IRQ

which enable to turn forwarded IRQ mode on/off.

the kvm_arch_forwarded_irq struct embodies a forwarded IRQ

Signed-off-by: Eric Auger <eric.auger at linaro.org>

---

v1 -> v2:
- struct kvm_arch_forwarded_irq moved from arch/arm/include/uapi/asm/kvm.h
  to include/uapi/linux/kvm.h
  also irq_index renamed into index and guest_irq renamed into gsi
- ASSIGN/DEASSIGN renamed into FORWARD/UNFORWARD
---
 Documentation/virtual/kvm/devices/vfio.txt | 26 ++++++++++++++++++++++++++
 include/uapi/linux/kvm.h                   |  9 +++++++++
 2 files changed, 35 insertions(+)

diff --git a/Documentation/virtual/kvm/devices/vfio.txt b/Documentation/virtual/kvm/devices/vfio.txt
index ef51740..048baa0 100644
--- a/Documentation/virtual/kvm/devices/vfio.txt
+++ b/Documentation/virtual/kvm/devices/vfio.txt
@@ -13,6 +13,7 @@ VFIO-group is held by KVM.
 
 Groups:
   KVM_DEV_VFIO_GROUP
+  KVM_DEV_VFIO_DEVICE
 
 KVM_DEV_VFIO_GROUP attributes:
   KVM_DEV_VFIO_GROUP_ADD: Add a VFIO group to VFIO-KVM device tracking
@@ -20,3 +21,28 @@ KVM_DEV_VFIO_GROUP attributes:
 
 For each, kvm_device_attr.addr points to an int32_t file descriptor
 for the VFIO group.
+
+KVM_DEV_VFIO_DEVICE attributes:
+  KVM_DEV_VFIO_DEVICE_FORWARD_IRQ
+  KVM_DEV_VFIO_DEVICE_UNFORWARD_IRQ
+
+For each, kvm_device_attr.addr points to a kvm_arch_forwarded_irq struct.
+This user API makes possible to create a special IRQ handling mode,
+where KVM and a VFIO platform driver collaborate to improve IRQ
+handling performance.
+
+fd represents the file descriptor of a valid VFIO device whose physical
+IRQ, referenced by its index, is injected into the VM guest irq (gsi).
+
+On FORWARD_IRQ, KVM-VFIO device programs:
+- the host, to not complete the physical IRQ itself.
+- the GIC, to automatically complete the physical IRQ when the guest
+  completes the virtual IRQ.
+This avoids trapping the end-of-interrupt for level sensitive IRQ.
+
+On UNFORWARD_IRQ, one returns to the mode where the host completes the
+physical IRQ and the guest completes the virtual IRQ.
+
+It is up to the caller of this API to make sure the IRQ is not
+outstanding when the FORWARD/UNFORWARD is called. This could lead to
+some inconsistency on who is going to complete the IRQ.
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index cf3a2ff..8cd7b0e 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -947,6 +947,12 @@ struct kvm_device_attr {
 	__u64	addr;		/* userspace address of attr data */
 };
 
+struct kvm_arch_forwarded_irq {
+	__u32 fd; /* file desciptor of the VFIO device */
+	__u32 index; /* VFIO device IRQ index */
+	__u32 gsi; /* gsi, ie. virtual IRQ number */
+};
+
 #define KVM_DEV_TYPE_FSL_MPIC_20	1
 #define KVM_DEV_TYPE_FSL_MPIC_42	2
 #define KVM_DEV_TYPE_XICS		3
@@ -954,6 +960,9 @@ struct kvm_device_attr {
 #define  KVM_DEV_VFIO_GROUP			1
 #define   KVM_DEV_VFIO_GROUP_ADD			1
 #define   KVM_DEV_VFIO_GROUP_DEL			2
+#define  KVM_DEV_VFIO_DEVICE			2
+#define   KVM_DEV_VFIO_DEVICE_FORWARD_IRQ			1
+#define   KVM_DEV_VFIO_DEVICE_UNFORWARD_IRQ			2
 #define KVM_DEV_TYPE_ARM_VGIC_V2	5
 #define KVM_DEV_TYPE_FLIC		6
 
-- 
1.9.1