KVM: Introduce direct MSI message injection for in-kernel irqchips

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 has to manage
carefully.

By providing a direct injection path, we can both avoid using up limited
resources and simplify the necessary steps for user land.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

7 files changed, 66 insertions, 0 deletions

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 81ff39f6248d..a1552210b16d 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1689,6 +1689,27 @@ where the guest will clear the flag: when the soft lockup watchdog timer resets
 itself or when a soft lockup is detected.  This ioctl can be called any time
 after pausing the vcpu, but before it is resumed.
 
+4.71 KVM_SIGNAL_MSI
+
+Capability: KVM_CAP_SIGNAL_MSI
+Architectures: x86
+Type: vm ioctl
+Parameters: struct kvm_msi (in)
+Returns: >0 on delivery, 0 if guest blocked the MSI, and -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];
+};
+
+No flags are defined so far. The corresponding field must be 0.
+
 5. The kvm_run structure
 
 Application code obtains a pointer to the kvm_run structure by
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 1a7fe868f375..a28f338843ea 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -36,6 +36,7 @@ config KVM
         select TASKSTATS
         select TASK_DELAY_ACCT
         select PERF_EVENTS
+        select HAVE_KVM_MSI
         ---help---
           Support hosting fully virtualized guest machines using hardware
           virtualization extensions.  You will need a fairly recent
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 7a9dd4b3dede..225b452e1d1d 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -590,6 +590,7 @@ struct kvm_ppc_pvinfo {
 #define KVM_CAP_SYNC_REGS 74
 #define KVM_CAP_PCI_2_3 75
 #define KVM_CAP_KVMCLOCK_CTRL 76
+#define KVM_CAP_SIGNAL_MSI 77
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -715,6 +716,14 @@ struct kvm_one_reg {
         __u64 addr;
 };
 
+struct kvm_msi {
+        __u32 address_lo;
+        __u32 address_hi;
+        __u32 data;
+        __u32 flags;
+        __u8  pad[16];
+};
+
 /*
  * ioctls for VM fds
  */
@@ -789,6 +798,8 @@ struct kvm_s390_ucas_mapping {
 /* Available with KVM_CAP_PCI_2_3 */
 #define KVM_ASSIGN_SET_INTX_MASK  _IOW(KVMIO,  0xa4, \
                                        struct kvm_assigned_pci_dev)
+/* Available with KVM_CAP_SIGNAL_MSI */
+#define KVM_SIGNAL_MSI            _IOW(KVMIO,  0xa5, struct kvm_msi)
 
 /*
  * ioctls for vcpu fds
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 186ffab0b9f0..6f343307d72b 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -802,6 +802,8 @@ int kvm_set_irq_routing(struct kvm *kvm,
                         unsigned flags);
 void kvm_free_irq_routing(struct kvm *kvm);
 
+int kvm_send_userspace_msi(struct kvm *kvm, struct kvm_msi *msi);
+
 #else
 
 static inline void kvm_free_irq_routing(struct kvm *kvm) {}
diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
index f63ccb0a5982..28694f4a9139 100644
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -18,3 +18,6 @@ config KVM_MMIO
 
 config KVM_ASYNC_PF
        bool
+
+config HAVE_KVM_MSI
+       bool
diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
index 9f614b4e365f..a6a0365475ed 100644
--- a/virt/kvm/irq_comm.c
+++ b/virt/kvm/irq_comm.c
@@ -138,6 +138,20 @@ int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
         return kvm_irq_delivery_to_apic(kvm, NULL, &irq);
 }
 
+int kvm_send_userspace_msi(struct kvm *kvm, struct kvm_msi *msi)
+{
+        struct kvm_kernel_irq_routing_entry route;
+
+        if (!irqchip_in_kernel(kvm) || msi->flags != 0)
+                return -EINVAL;
+
+        route.msi.address_lo = msi->address_lo;
+        route.msi.address_hi = msi->address_hi;
+        route.msi.data = msi->data;
+
+        return kvm_set_msi(&route, kvm, KVM_USERSPACE_IRQ_SOURCE_ID, 1);
+}
+
 /*
  * Return value:
  *  < 0   Interrupt was ignored (masked or not delivered for other reasons)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 9eb7936e491d..1847c762d8d9 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2060,6 +2060,17 @@ static long kvm_vm_ioctl(struct file *filp,
                 mutex_unlock(&kvm->lock);
                 break;
 #endif
+#ifdef CONFIG_HAVE_KVM_MSI
+        case KVM_SIGNAL_MSI: {
+                struct kvm_msi msi;
+
+                r = -EFAULT;
+                if (copy_from_user(&msi, argp, sizeof msi))
+                        goto out;
+                r = kvm_send_userspace_msi(kvm, &msi);
+                break;
+        }
+#endif
         default:
                 r = kvm_arch_vm_ioctl(filp, ioctl, arg);
                 if (r == -ENOTTY)
@@ -2188,6 +2199,9 @@ static long kvm_dev_ioctl_check_extension_generic(long arg)
         case KVM_CAP_SET_BOOT_CPU_ID:
 #endif
         case KVM_CAP_INTERNAL_ERROR_DATA:
+#ifdef CONFIG_HAVE_KVM_MSI
+        case KVM_CAP_SIGNAL_MSI:
+#endif
                 return 1;
 #ifdef CONFIG_HAVE_KVM_IRQCHIP
         case KVM_CAP_IRQ_ROUTING: