[PATCH] KVM: Hyper-V: do not do hypercall userspace exits if SynIC is disabled

[Paolo Bonzini <pbonzini@redhat.com>]

If SynIC is disabled, there is nothing that userspace can do to
handle these exits; on the other hand, userspace probably will
not know about KVM_EXIT_HYPERV_HCALL and complain about it or
even exit.  Just prevent anything bad from happening by handling
the hypercall in KVM and returning an "invalid hypercall" code.

Fixes: 83326e43f27e9a8a501427a0060f8af519a39bb2
Cc: Andrey Smetanin <asmetanin@virtuozzo.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/hyperv.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index b960d9ea171f..9e2becd20a59 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1237,14 +1237,17 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
 		break;
 	case HVCALL_POST_MESSAGE:
 	case HVCALL_SIGNAL_EVENT:
-		vcpu->run->exit_reason = KVM_EXIT_HYPERV;
-		vcpu->run->hyperv.type = KVM_EXIT_HYPERV_HCALL;
-		vcpu->run->hyperv.u.hcall.input = param;
-		vcpu->run->hyperv.u.hcall.params[0] = ingpa;
-		vcpu->run->hyperv.u.hcall.params[1] = outgpa;
-		vcpu->arch.complete_userspace_io =
+		if (vcpu_to_synic(vcpu)->active) {
+			vcpu->run->exit_reason = KVM_EXIT_HYPERV;
+			vcpu->run->hyperv.type = KVM_EXIT_HYPERV_HCALL;
+			vcpu->run->hyperv.u.hcall.input = param;
+			vcpu->run->hyperv.u.hcall.params[0] = ingpa;
+			vcpu->run->hyperv.u.hcall.params[1] = outgpa;
+			vcpu->arch.complete_userspace_io =
 				kvm_hv_hypercall_complete_userspace;
-		return 0;
+			return 0;
+		}
+		/* fall through */
 	default:
 		res = HV_STATUS_INVALID_HYPERCALL_CODE;
 		break;
-- 
1.8.3.1