4 files changed, 24 insertions, 20 deletions
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 472544cf1de2..9b59e63567bb 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2522,7 +2522,7 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD))
 			return 1;
 
-		if (data & ~kvm_spec_ctrl_valid_bits(vcpu))
+		if (kvm_spec_ctrl_test_value(data))
 			return 1;
 
 		svm->spec_ctrl = data;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index c6e96e2ef4d6..0d526b32f041 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2062,7 +2062,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
 			return 1;
 
-		if (data & ~kvm_spec_ctrl_valid_bits(vcpu))
+		if (kvm_spec_ctrl_test_value(data))
 			return 1;
 
 		vmx->spec_ctrl = data;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c432a445cbbe..7f32169e8449 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10693,28 +10693,32 @@ bool kvm_arch_no_poll(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_arch_no_poll);
 
-u64 kvm_spec_ctrl_valid_bits(struct kvm_vcpu *vcpu)
+
+int kvm_spec_ctrl_test_value(u64 value)
 {
-	uint64_t bits = SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_SSBD;
+	/*
+	 * test that setting IA32_SPEC_CTRL to given value
+	 * is allowed by the host processor
+	 */
+
+	u64 saved_value;
+	unsigned long flags;
+	int ret = 0;
 
-	/* The STIBP bit doesn't fault even if it's not advertised */
-	if (!guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) &&
-	    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS))
-		bits &= ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP);
-	if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL) &&
-	    !boot_cpu_has(X86_FEATURE_AMD_IBRS))
-		bits &= ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP);
+	local_irq_save(flags);
 
-	if (!guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL_SSBD) &&
-	    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD))
-		bits &= ~SPEC_CTRL_SSBD;
-	if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) &&
-	    !boot_cpu_has(X86_FEATURE_AMD_SSBD))
-		bits &= ~SPEC_CTRL_SSBD;
+	if (rdmsrl_safe(MSR_IA32_SPEC_CTRL, &saved_value))
+		ret = 1;
+	else if (wrmsrl_safe(MSR_IA32_SPEC_CTRL, value))
+		ret = 1;
+	else
+		wrmsrl(MSR_IA32_SPEC_CTRL, saved_value);
 
-	return bits;
+	local_irq_restore(flags);
+
+	return ret;
 }
-EXPORT_SYMBOL_GPL(kvm_spec_ctrl_valid_bits);
+EXPORT_SYMBOL_GPL(kvm_spec_ctrl_test_value);
 
 EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit);
 EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_fast_mmio);
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 224670d7c245..3308c3ccc0fd 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -368,7 +368,7 @@ static inline bool kvm_dr6_valid(u64 data)
 
 void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu);
 void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu);
-u64 kvm_spec_ctrl_valid_bits(struct kvm_vcpu *vcpu);
+int kvm_spec_ctrl_test_value(u64 value);
 int kvm_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
 bool kvm_vcpu_exit_request(struct kvm_vcpu *vcpu);