KVM: Allow internal errors reported to userspace to carry extra data

Usually userspace will freeze the guest so we can inspect it, but some
internal state is not available.  Add extra data to internal error
reporting so we can expose it to the debugger.  Extra data is specific
to the suberror.

Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/mmu.c

@@ -2800,6 +2800,7 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u32 error_code)
 	case EMULATE_FAIL:
 		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
 		vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
+		vcpu->run->internal.ndata = 0;
 		return 0;
 	default:
 		BUG();

arch/x86/kvm/vmx.c

@@ -3352,6 +3352,7 @@ static int handle_invalid_guest_state(struct kvm_vcpu *vcpu)
 			kvm_report_emulation_failure(vcpu, "emulation failure");
 			vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
 			vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
+			vcpu->run->internal.ndata = 0;
 			ret = 0;
 			goto out;
 		}