KVM: x86: reinstate vendor-agnostic check on SPEC_CTRL cpuid bits

Until commit e7c587da ("x86/speculation: Use synthetic bits for
IBRS/IBPB/STIBP"), KVM was testing both Intel and AMD CPUID bits before
allowing the guest to write MSR_IA32_SPEC_CTRL and MSR_IA32_PRED_CMD.
Testing only Intel bits on VMX processors, or only AMD bits on SVM
processors, fails if the guests are created with the "opposite" vendor
as the host.

While at it, also tweak the host CPU check to use the vendor-agnostic
feature bit X86_FEATURE_IBPB, since we only care about the availability
of the MSR on the host here and not about specific CPUID bits.

Fixes: e7c587da ("x86/speculation: Use synthetic bits for IBRS/IBPB/STIBP")
Cc: stable@vger.kernel.org
Reported-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/cpuid.h

@@ -264,6 +264,20 @@ static inline int guest_cpuid_stepping(struct kvm_vcpu *vcpu)
 	return x86_stepping(best->eax);
 }
 
+static inline bool guest_has_spec_ctrl_msr(struct kvm_vcpu *vcpu)
+{
+	return (guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) ||
+		guest_cpuid_has(vcpu, X86_FEATURE_AMD_STIBP) ||
+		guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS) ||
+		guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD));
+}
+
+static inline bool guest_has_pred_cmd_msr(struct kvm_vcpu *vcpu)
+{
+	return (guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) ||
+		guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBPB));
+}
+
 static inline bool supports_cpuid_fault(struct kvm_vcpu *vcpu)
 {
 	return vcpu->arch.msr_platform_info & MSR_PLATFORM_INFO_CPUID_FAULT;

arch/x86/kvm/svm/svm.c

@@ -2545,10 +2545,7 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		break;
 	case MSR_IA32_SPEC_CTRL:
 		if (!msr_info->host_initiated &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_STIBP) &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS) &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD))
+		    !guest_has_spec_ctrl_msr(vcpu))
 			return 1;
 
 		msr_info->data = svm->spec_ctrl;
@@ -2632,10 +2629,7 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 		break;
 	case MSR_IA32_SPEC_CTRL:
 		if (!msr->host_initiated &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_STIBP) &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS) &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD))
+		    !guest_has_spec_ctrl_msr(vcpu))
 			return 1;
 
 		if (kvm_spec_ctrl_test_value(data))
@@ -2660,12 +2654,12 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 		break;
 	case MSR_IA32_PRED_CMD:
 		if (!msr->host_initiated &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBPB))
+		    !guest_has_pred_cmd_msr(vcpu))
 			return 1;
 
 		if (data & ~PRED_CMD_IBPB)
 			return 1;
-		if (!boot_cpu_has(X86_FEATURE_AMD_IBPB))
+		if (!boot_cpu_has(X86_FEATURE_IBPB))
 			return 1;
 		if (!data)
 			break;

arch/x86/kvm/vmx/vmx.c

@@ -1826,7 +1826,7 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		break;
 	case MSR_IA32_SPEC_CTRL:
 		if (!msr_info->host_initiated &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
+		    !guest_has_spec_ctrl_msr(vcpu))
 			return 1;
 
 		msr_info->data = to_vmx(vcpu)->spec_ctrl;
@@ -2028,7 +2028,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		break;
 	case MSR_IA32_SPEC_CTRL:
 		if (!msr_info->host_initiated &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
+		    !guest_has_spec_ctrl_msr(vcpu))
 			return 1;
 
 		if (kvm_spec_ctrl_test_value(data))
@@ -2063,12 +2063,12 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		goto find_uret_msr;
 	case MSR_IA32_PRED_CMD:
 		if (!msr_info->host_initiated &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
+		    !guest_has_pred_cmd_msr(vcpu))
 			return 1;
 
 		if (data & ~PRED_CMD_IBPB)
 			return 1;
-		if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL))
+		if (!boot_cpu_has(X86_FEATURE_IBPB))
 			return 1;
 		if (!data)
 			break;