kvm: svm: move WARN_ON in svm_adjust_tsc_offset

When running the tsc_adjust kvm-unit-test on an AMD processor with the
IA32_TSC_ADJUST feature enabled, the WARN_ON in svm_adjust_tsc_offset can be
triggered. This WARN_ON checks for a negative adjustment in case __scale_tsc
is called; however it may trigger unnecessary warnings.

This patch moves the WARN_ON to trigger only if __scale_tsc will actually be
called from svm_adjust_tsc_offset. In addition make adj in kvm_set_msr_common
s64 since this can have signed values.
Signed-off-by: Chris J Arges <chris.j.arges@canonical.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm.c

@@ -1056,9 +1056,11 @@ static void svm_adjust_tsc_offset(struct kvm_vcpu *vcpu, s64 adjustment, bool ho
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
+	if (host) {
+		if (svm->tsc_ratio != TSC_RATIO_DEFAULT)
 			WARN_ON(adjustment < 0);
-	if (host)
-		adjustment = svm_scale_tsc(vcpu, adjustment);
+		adjustment = svm_scale_tsc(vcpu, (u64)adjustment);
+	}
 
 	svm->vmcb->control.tsc_offset += adjustment;
 	if (is_guest_mode(vcpu))

arch/x86/kvm/x86.c

@@ -2143,7 +2143,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_IA32_TSC_ADJUST:
 		if (guest_cpuid_has_tsc_adjust(vcpu)) {
 			if (!msr_info->host_initiated) {
-				u64 adj = data - vcpu->arch.ia32_tsc_adjust_msr;
+				s64 adj = data - vcpu->arch.ia32_tsc_adjust_msr;
 				kvm_x86_ops->adjust_tsc_offset(vcpu, adj, true);
 			}
 			vcpu->arch.ia32_tsc_adjust_msr = data;