KVM: x86/xen: Add KVM_IRQ_ROUTING_XEN_EVTCHN and event channel delivery

This adds basic support for delivering 2 level event channels to a guest.

Initially, it only supports delivery via the IRQ routing table, triggered
by an eventfd. In order to do so, it has a kvm_xen_set_evtchn_fast()
function which will use the pre-mapped shared_info page if it already
exists and is still valid, while the slow path through the irqfd_inject
workqueue will remap the shared_info page if necessary.

It sets the bits in the shared_info page but not the vcpu_info; that is
deferred to __kvm_xen_has_interrupt() which raises the vector to the
appropriate vCPU.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

Documentation/virt/kvm/api.rst

@@ -1799,6 +1799,7 @@ No flags are specified so far, the corresponding field must be set to zero.
 		struct kvm_irq_routing_msi msi;
 		struct kvm_irq_routing_s390_adapter adapter;
 		struct kvm_irq_routing_hv_sint hv_sint;
+		struct kvm_irq_routing_xen_evtchn xen_evtchn;
 		__u32 pad[8];
 	} u;
   };
@@ -1808,6 +1809,7 @@ No flags are specified so far, the corresponding field must be set to zero.
   #define KVM_IRQ_ROUTING_MSI 2
   #define KVM_IRQ_ROUTING_S390_ADAPTER 3
   #define KVM_IRQ_ROUTING_HV_SINT 4
+  #define KVM_IRQ_ROUTING_XEN_EVTCHN 5
 
 flags:
 
@@ -1859,6 +1861,20 @@ address_hi must be zero.
 	__u32 sint;
   };
 
+  struct kvm_irq_routing_xen_evtchn {
+	__u32 port;
+	__u32 vcpu;
+	__u32 priority;
+  };
+
+
+When KVM_CAP_XEN_HVM includes the KVM_XEN_HVM_CONFIG_EVTCHN_2LEVEL bit
+in its indication of supported features, routing to Xen event channels
+is supported. Although the priority field is present, only the value
+KVM_XEN_HVM_CONFIG_EVTCHN_2LEVEL is supported, which means delivery by
+2 level event channels. FIFO event channel support may be added in
+the future.
+
 
 4.55 KVM_SET_TSC_KHZ
 --------------------
@@ -7413,6 +7429,7 @@ PVHVM guests. Valid flags are::
   #define KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL	(1 << 1)
   #define KVM_XEN_HVM_CONFIG_SHARED_INFO	(1 << 2)
   #define KVM_XEN_HVM_CONFIG_RUNSTATE		(1 << 2)
+  #define KVM_XEN_HVM_CONFIG_EVTCHN_2LEVEL	(1 << 3)
 
 The KVM_XEN_HVM_CONFIG_HYPERCALL_MSR flag indicates that the KVM_XEN_HVM_CONFIG
 ioctl is available, for the guest to set its hypercall page.
@@ -7432,6 +7449,10 @@ The KVM_XEN_HVM_CONFIG_RUNSTATE flag indicates that the runstate-related
 features KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_ADDR/_CURRENT/_DATA/_ADJUST are
 supported by the KVM_XEN_VCPU_SET_ATTR/KVM_XEN_VCPU_GET_ATTR ioctls.
 
+The KVM_XEN_HVM_CONFIG_EVTCHN_2LEVEL flag indicates that IRQ routing entries
+of the type KVM_IRQ_ROUTING_XEN_EVTCHN are supported, with the priority
+field set to indicate 2 level event channel delivery.
+
 8.31 KVM_CAP_PPC_MULTITCE
 -------------------------
 

arch/x86/include/asm/kvm_host.h

@@ -604,6 +604,7 @@ struct kvm_vcpu_xen {
 	u64 last_steal;
 	u64 runstate_entry_time;
 	u64 runstate_times[4];
+	unsigned long evtchn_pending_sel;
 };
 
 struct kvm_vcpu_arch {

arch/x86/kvm/irq_comm.c

@@ -24,6 +24,7 @@
 
 #include "hyperv.h"
 #include "x86.h"
+#include "xen.h"
 
 static int kvm_set_pic_irq(struct kvm_kernel_irq_routing_entry *e,
 			   struct kvm *kvm, int irq_source_id, int level,
@@ -175,6 +176,13 @@ int kvm_arch_set_irq_inatomic(struct kvm_kernel_irq_routing_entry *e,
 			return r;
 		break;
 
+#ifdef CONFIG_KVM_XEN
+	case KVM_IRQ_ROUTING_XEN_EVTCHN:
+		if (!level)
+			return -1;
+
+		return kvm_xen_set_evtchn_fast(e, kvm);
+#endif
 	default:
 		break;
 	}
@@ -310,6 +318,10 @@ int kvm_set_routing_entry(struct kvm *kvm,
 		e->hv_sint.vcpu = ue->u.hv_sint.vcpu;
 		e->hv_sint.sint = ue->u.hv_sint.sint;
 		break;
+#ifdef CONFIG_KVM_XEN
+	case KVM_IRQ_ROUTING_XEN_EVTCHN:
+		return kvm_xen_setup_evtchn(kvm, e, ue);
+#endif
 	default:
 		return -EINVAL;
 	}

arch/x86/kvm/x86.c

@@ -4147,7 +4147,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_XEN_HVM:
 		r = KVM_XEN_HVM_CONFIG_HYPERCALL_MSR |
 		    KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL |
-		    KVM_XEN_HVM_CONFIG_SHARED_INFO;
+		    KVM_XEN_HVM_CONFIG_SHARED_INFO |
+		    KVM_XEN_HVM_CONFIG_EVTCHN_2LEVEL;
 		if (sched_info_on())
 			r |= KVM_XEN_HVM_CONFIG_RUNSTATE;
 		break;