KVM: x86/xen: Use gfn_to_pfn_cache for vcpu_info

Currently, the fast path of kvm_xen_set_evtchn_fast() doesn't set the
index bits in the target vCPU's evtchn_pending_sel, because it only has
a userspace virtual address with which to do so. It just sets them in
the kernel, and kvm_xen_has_interrupt() then completes the delivery to
the actual vcpu_info structure when the vCPU runs.

Using a gfn_to_pfn_cache allows kvm_xen_set_evtchn_fast() to do the full
delivery in the common case.

Clean up the fallback case too, by moving the deferred delivery out into
a separate kvm_xen_inject_pending_events() function which isn't ever
called in atomic contexts as __kvm_xen_has_interrupt() is.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-6-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -606,9 +606,8 @@ struct kvm_vcpu_hv {
 struct kvm_vcpu_xen {
 	u64 hypercall_rip;
 	u32 current_runstate;
-	bool vcpu_info_set;
 	bool vcpu_time_info_set;
-	struct gfn_to_hva_cache vcpu_info_cache;
+	struct gfn_to_pfn_cache vcpu_info_cache;
 	struct gfn_to_hva_cache vcpu_time_info_cache;
 	struct gfn_to_pfn_cache runstate_cache;
 	u64 last_steal;

arch/x86/kvm/x86.c

@@ -3158,8 +3158,8 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
 
 	if (vcpu->pv_time.active)
 		kvm_setup_guest_pvclock(v, &vcpu->pv_time, 0);
-	if (vcpu->xen.vcpu_info_set)
-		kvm_setup_pvclock_page(v, &vcpu->xen.vcpu_info_cache,
+	if (vcpu->xen.vcpu_info_cache.active)
+		kvm_setup_guest_pvclock(v, &vcpu->xen.vcpu_info_cache,
 					offsetof(struct compat_vcpu_info, time));
 	if (vcpu->xen.vcpu_time_info_set)
 		kvm_setup_pvclock_page(v, &vcpu->xen.vcpu_time_info_cache, 0);
@@ -10424,6 +10424,9 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
 			break;
 
 		kvm_clear_request(KVM_REQ_UNBLOCK, vcpu);
+		if (kvm_xen_has_pending_events(vcpu))
+			kvm_xen_inject_pending_events(vcpu);
+
 		if (kvm_cpu_has_pending_timer(vcpu))
 			kvm_inject_pending_timer_irqs(vcpu);
 
@@ -12236,6 +12239,9 @@ static inline bool kvm_vcpu_has_events(struct kvm_vcpu *vcpu)
 	    kvm_x86_ops.nested_ops->hv_timer_pending(vcpu))
 		return true;
 
+	if (kvm_xen_has_pending_events(vcpu))
+		return true;
+
 	return false;
 }
 

arch/x86/kvm/xen.h

@@ -15,6 +15,7 @@
 extern struct static_key_false_deferred kvm_xen_enabled;
 
 int __kvm_xen_has_interrupt(struct kvm_vcpu *vcpu);
+void kvm_xen_inject_pending_events(struct kvm_vcpu *vcpu);
 int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data);
 int kvm_xen_vcpu_get_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data);
 int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data);
@@ -46,11 +47,19 @@ static inline bool kvm_xen_hypercall_enabled(struct kvm *kvm)
 static inline int kvm_xen_has_interrupt(struct kvm_vcpu *vcpu)
 {
 	if (static_branch_unlikely(&kvm_xen_enabled.key) &&
-	    vcpu->arch.xen.vcpu_info_set && vcpu->kvm->arch.xen.upcall_vector)
+	    vcpu->arch.xen.vcpu_info_cache.active &&
+	    vcpu->kvm->arch.xen.upcall_vector)
 		return __kvm_xen_has_interrupt(vcpu);
 
 	return 0;
 }
+
+static inline bool kvm_xen_has_pending_events(struct kvm_vcpu *vcpu)
+{
+	return static_branch_unlikely(&kvm_xen_enabled.key) &&
+		vcpu->arch.xen.evtchn_pending_sel;
+}
+
 #else
 static inline int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
 {
@@ -83,6 +92,15 @@ static inline int kvm_xen_has_interrupt(struct kvm_vcpu *vcpu)
 {
 	return 0;
 }
+
+static inline void kvm_xen_inject_pending_events(struct kvm_vcpu *vcpu)
+{
+}
+
+static inline bool kvm_xen_has_pending_events(struct kvm_vcpu *vcpu)
+{
+	return false;
+}
 #endif
 
 int kvm_xen_hypercall(struct kvm_vcpu *vcpu);