[RFC][PATCH] KVM: Introduce direct MSI message injection for in-kernel irqchips

[Jan Kiszka <jan.kiszka@siemens.com>]

Currently, MSI messages can only be injected to in-kernel irqchips by
defining a corresponding IRQ route for each message. This is not only
unhandy if the MSI messages are generated "on the fly" by user space,
IRQ routes are a limited resource that user space as to manage
carefully.

By providing a direct injection with, we can both avoid using up limited
resources and simplify the necessary steps for user land. The API
already provides a channel (flags) to revoke an injected but not yet
delivered message which will become important for in-kernel MSI-X vector
masking support.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
 Documentation/virtual/kvm/api.txt |   23 +++++++++++++++++++++++
 include/linux/kvm.h               |   15 +++++++++++++++
 virt/kvm/kvm_main.c               |   18 ++++++++++++++++++
 3 files changed, 56 insertions(+), 0 deletions(-)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 7945b0b..f4c3de3 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1383,6 +1383,29 @@ The following flags are defined:
 If datamatch flag is set, the event will be signaled only if the written value
 to the registered address is equal to datamatch in struct kvm_ioeventfd.
 
+4.59 KVM_SET_MSI
+
+Capability: KVM_CAP_SET_MSI
+Architectures: x86 ia64
+Type: vm ioctl
+Parameters: struct kvm_msi (in)
+Returns: 0 on success, -1 on error
+
+Directly inject a MSI message. Only valid with in-kernel irqchip that handles
+MSI messages.
+
+struct kvm_msi {
+	__u32 address_lo;
+	__u32 address_hi;
+	__u32 data;
+	__u32 flags;
+	__u8  pad[16];
+};
+
+The following flags are defined:
+
+#define KVM_MSI_FLAG_RAISE     (1 << 0)
+
 4.62 KVM_CREATE_SPAPR_TCE
 
 Capability: KVM_CAP_SPAPR_TCE
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 6884054..83875ed 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -557,6 +557,9 @@ struct kvm_ppc_pvinfo {
 #define KVM_CAP_PPC_HIOR 67
 #define KVM_CAP_PPC_PAPR 68
 #define KVM_CAP_S390_GMAP 71
+#ifdef __KVM_HAVE_MSI
+#define KVM_CAP_SET_MSI 72
+#endif
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -636,6 +639,16 @@ struct kvm_clock_data {
 	__u32 pad[9];
 };
 
+#define KVM_MSI_FLAG_RAISE     (1 << 0)
+
+struct kvm_msi {
+	__u32 address_lo;
+	__u32 address_hi;
+	__u32 data;
+	__u32 flags;
+	__u8  pad[16];
+};
+
 /*
  * ioctls for VM fds
  */
@@ -696,6 +709,8 @@ struct kvm_clock_data {
 /* Available with KVM_CAP_TSC_CONTROL */
 #define KVM_SET_TSC_KHZ           _IO(KVMIO,  0xa2)
 #define KVM_GET_TSC_KHZ           _IO(KVMIO,  0xa3)
+/* Available with KVM_CAP_SET_MSI */
+#define KVM_SET_MSI               _IOW(KVMIO,  0xa4, struct kvm_msi)
 
 /*
  * ioctls for vcpu fds
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d9cfb78..0e3a947 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2058,6 +2058,24 @@ static long kvm_vm_ioctl(struct file *filp,
 		mutex_unlock(&kvm->lock);
 		break;
 #endif
+#ifdef __KVM_HAVE_MSI
+	case KVM_SET_MSI: {
+		struct kvm_kernel_irq_routing_entry route;
+		struct kvm_msi msi;
+
+		r = -EFAULT;
+		if (copy_from_user(&msi, argp, sizeof msi))
+			goto out;
+		route.msi.address_lo = msi.address_lo;
+		route.msi.address_hi = msi.address_hi;
+		route.msi.data = msi.data;
+		r = 0;
+		if (msi.flags & KVM_MSI_FLAG_RAISE)
+			r =  kvm_set_msi(&route, kvm,
+					 KVM_USERSPACE_IRQ_SOURCE_ID, 1);
+		break;
+	}
+#endif
 	default:
 		r = kvm_arch_vm_ioctl(filp, ioctl, arg);
 		if (r == -ENOTTY)
-- 
1.7.3.4