kvm: svm: Add IA32_FLUSH_CMD guest support

Expose IA32_FLUSH_CMD to the guest if the guest CPUID enumerates
support for this MSR. As with IA32_PRED_CMD, permission for
unintercepted writes to this MSR will be granted to the guest after
the first non-zero write.
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20230201132905.549148-3-eesposit@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/svm.c

@@ -2869,6 +2869,28 @@ static int svm_set_vm_cr(struct kvm_vcpu *vcpu, u64 data)
 	return 0;
 }
 
+static int svm_set_msr_ia32_cmd(struct kvm_vcpu *vcpu, struct msr_data *msr,
+				bool guest_has_feat, u64 cmd,
+				int x86_feature_bit)
+{
+	struct vcpu_svm *svm = to_svm(vcpu);
+
+	if (!msr->host_initiated && !guest_has_feat)
+		return 1;
+
+	if (!(msr->data & ~cmd))
+		return 1;
+	if (!boot_cpu_has(x86_feature_bit))
+		return 1;
+	if (!msr->data)
+		return 0;
+
+	wrmsrl(msr->index, cmd);
+	set_msr_interception(vcpu, svm->msrpm, msr->index, 0, 1);
+
+	return 0;
+}
+
 static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -2943,19 +2965,14 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SPEC_CTRL, 1, 1);
 		break;
 	case MSR_IA32_PRED_CMD:
-		if (!msr->host_initiated &&
-		    !guest_has_pred_cmd_msr(vcpu))
-			return 1;
-
-		if (data & ~PRED_CMD_IBPB)
-			return 1;
-		if (!boot_cpu_has(X86_FEATURE_IBPB))
-			return 1;
-		if (!data)
-			break;
-
-		wrmsrl(MSR_IA32_PRED_CMD, PRED_CMD_IBPB);
-		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_PRED_CMD, 0, 1);
+		r = svm_set_msr_ia32_cmd(vcpu, msr,
+					 guest_has_pred_cmd_msr(vcpu),
+					 PRED_CMD_IBPB, X86_FEATURE_IBPB);
+		break;
+	case MSR_IA32_FLUSH_CMD:
+		r = svm_set_msr_ia32_cmd(vcpu, msr,
+					 guest_cpuid_has(vcpu, X86_FEATURE_FLUSH_L1D),
+					 L1D_FLUSH, X86_FEATURE_FLUSH_L1D);
 		break;
 	case MSR_AMD64_VIRT_SPEC_CTRL:
 		if (!msr->host_initiated &&