kvm: vmx: 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.
Co-developed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20230201132905.549148-2-eesposit@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -654,6 +654,9 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
 	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
 					 MSR_IA32_PRED_CMD, MSR_TYPE_W);
 
+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
+					 MSR_IA32_FLUSH_CMD, MSR_TYPE_W);
+
 	kvm_vcpu_unmap(vcpu, &vmx->nested.msr_bitmap_map, false);
 
 	vmx->nested.force_msr_bitmap_recalc = false;

arch/x86/kvm/vmx/vmx.c

@@ -2133,6 +2133,39 @@ static u64 vmx_get_supported_debugctl(struct kvm_vcpu *vcpu, bool host_initiated
 	return debugctl;
 }
 
+static int vmx_set_msr_ia32_cmd(struct kvm_vcpu *vcpu,
+				struct msr_data *msr_info,
+				bool guest_has_feat, u64 cmd,
+				int x86_feature_bit)
+{
+	if (!msr_info->host_initiated && !guest_has_feat)
+		return 1;
+
+	if (!(msr_info->data & ~cmd))
+		return 1;
+	if (!boot_cpu_has(x86_feature_bit))
+		return 1;
+	if (!msr_info->data)
+		return 0;
+
+	wrmsrl(msr_info->index, cmd);
+
+	/*
+	 * For non-nested:
+	 * When it's written (to non-zero) for the first time, pass
+	 * it through.
+	 *
+	 * For nested:
+	 * The handling of the MSR bitmap for L2 guests is done in
+	 * nested_vmx_prepare_msr_bitmap. We should not touch the
+	 * vmcs02.msr_bitmap here since it gets completely overwritten
+	 * in the merging.
+	 */
+	vmx_disable_intercept_for_msr(vcpu, msr_info->index, MSR_TYPE_W);
+
+	return 0;
+}
+
 /*
  * Writes msr value into the appropriate "register".
  * Returns 0 on success, non-0 otherwise.
@@ -2286,31 +2319,16 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 			return 1;
 		goto find_uret_msr;
 	case MSR_IA32_PRED_CMD:
-		if (!msr_info->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);
-
-		/*
-		 * For non-nested:
-		 * When it's written (to non-zero) for the first time, pass
-		 * it through.
-		 *
-		 * For nested:
-		 * The handling of the MSR bitmap for L2 guests is done in
-		 * nested_vmx_prepare_msr_bitmap. We should not touch the
-		 * vmcs02.msr_bitmap here since it gets completely overwritten
-		 * in the merging.
-		 */
-		vmx_disable_intercept_for_msr(vcpu, MSR_IA32_PRED_CMD, MSR_TYPE_W);
+		ret = vmx_set_msr_ia32_cmd(vcpu, msr_info,
+					   guest_has_pred_cmd_msr(vcpu),
+					   PRED_CMD_IBPB,
+					   X86_FEATURE_IBPB);
+		break;
+	case MSR_IA32_FLUSH_CMD:
+		ret = vmx_set_msr_ia32_cmd(vcpu, msr_info,
+					   guest_cpuid_has(vcpu, X86_FEATURE_FLUSH_L1D),
+					   L1D_FLUSH,
+					   X86_FEATURE_FLUSH_L1D);
 		break;
 	case MSR_IA32_CR_PAT:
 		if (!kvm_pat_valid(data))