KVM: x86/xen: Support direct injection of event channel events

This adds a KVM_XEN_HVM_EVTCHN_SEND ioctl which allows direct injection
of events given an explicit { vcpu, port, priority } in precisely the
same form that those fields are given in the IRQ routing table.

Userspace is currently able to inject 2-level events purely by setting
the bits in the shared_info and vcpu_info, but FIFO event channels are
harder to deal with; we will need the kernel to take sole ownership of
delivery when we support those.

A patch advertising this feature with a new bit in the KVM_CAP_XEN_HVM
ioctl will be added in a subsequent patch.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-9-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 32 insertions, 0 deletions

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 9c87263a5be2..f0f0011c4617 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -1086,6 +1086,38 @@ int kvm_xen_setup_evtchn(struct kvm *kvm,
 	return 0;
 }
 
+/*
+ * Explicit event sending from userspace with KVM_XEN_HVM_EVTCHN_SEND ioctl.
+ */
+int kvm_xen_hvm_evtchn_send(struct kvm *kvm, struct kvm_irq_routing_xen_evtchn *uxe)
+{
+	struct kvm_xen_evtchn e;
+	int ret;
+
+	if (!uxe->port || uxe->port >= max_evtchn_port(kvm))
+		return -EINVAL;
+
+	/* We only support 2 level event channels for now */
+	if (uxe->priority != KVM_IRQ_ROUTING_XEN_EVTCHN_PRIO_2LEVEL)
+		return -EINVAL;
+
+	e.port = uxe->port;
+	e.vcpu_id = uxe->vcpu;
+	e.vcpu_idx = -1;
+	e.priority = uxe->priority;
+
+	ret = kvm_xen_set_evtchn(&e, kvm);
+
+	/*
+	 * None of that 'return 1 if it actually got delivered' nonsense.
+	 * We don't care if it was masked (-ENOTCONN) either.
+	 */
+	if (ret > 0 || ret == -ENOTCONN)
+		ret = 0;
+
+	return ret;
+}
+
 void kvm_xen_destroy_vcpu(struct kvm_vcpu *vcpu)
 {
 	kvm_gfn_to_pfn_cache_destroy(vcpu->kvm,