[PATCH 3.16 012/131] x86/KVM/VMX: Expose SPEC_CTRL Bit(2) to the guest

[Ben Hutchings]

3.16.59-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

commit da39556f66f5cfe8f9c989206974f1cb16ca5d7c upstream.

Expose the CPUID.7.EDX[31] bit to the guest, and also guard against various
combinations of SPEC_CTRL MSR values.

The handling of the MSR (to take into account the host value of SPEC_CTRL
Bit(2)) is taken care of in patch:

  KVM/SVM/VMX/x86/spectre_v2: Support the combination of guest and host IBRS

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Ingo Molnar <mingo@xxxxxxxxxx>

[dwmw2: Handle 4.9 guest CPUID differences, rename
        guest_cpu_has_ibrs() â guest_cpu_has_spec_ctrl()]
Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/x86/kvm/cpuid.c | 2 +-
 arch/x86/kvm/cpuid.h | 4 ++--
 arch/x86/kvm/svm.c   | 4 ++--
 arch/x86/kvm/vmx.c   | 6 +++---
 4 files changed, 8 insertions(+), 8 deletions(-)

--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -318,7 +318,7 @@ static inline int __do_cpuid_ent(struct
 
 	/* cpuid 7.0.edx*/
 	const u32 kvm_cpuid_7_0_edx_x86_features =
-		F(SPEC_CTRL) | F(ARCH_CAPABILITIES);
+		F(SPEC_CTRL) | F(RDS) | F(ARCH_CAPABILITIES);
 
 	/* all calls to cpuid_count() should be made on the same cpu */
 	get_cpu();
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -115,7 +115,7 @@ static inline bool guest_cpuid_has_ibpb(
 	return best && (best->edx & bit(X86_FEATURE_SPEC_CTRL));
 }
 
-static inline bool guest_cpuid_has_ibrs(struct kvm_vcpu *vcpu)
+static inline bool guest_cpuid_has_spec_ctrl(struct kvm_vcpu *vcpu)
 {
 	struct kvm_cpuid_entry2 *best;
 
@@ -123,7 +123,7 @@ static inline bool guest_cpuid_has_ibrs(
 	if (best && (best->ebx & bit(X86_FEATURE_IBRS)))
 		return true;
 	best = kvm_find_cpuid_entry(vcpu, 7, 0);
-	return best && (best->edx & bit(X86_FEATURE_SPEC_CTRL));
+	return best && (best->edx & (bit(X86_FEATURE_SPEC_CTRL) | bit(X86_FEATURE_RDS)));
 }
 
 static inline bool guest_cpuid_has_arch_capabilities(struct kvm_vcpu *vcpu)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -3139,7 +3139,7 @@ static int svm_get_msr(struct kvm_vcpu *
 		break;
 	case MSR_IA32_SPEC_CTRL:
 		if (!msr_info->host_initiated &&
-		    !guest_cpuid_has_ibrs(vcpu))
+		    !guest_cpuid_has_spec_ctrl(vcpu))
 			return 1;
 
 		msr_info->data = svm->spec_ctrl;
@@ -3218,7 +3218,7 @@ static int svm_set_msr(struct kvm_vcpu *
 		break;
 	case MSR_IA32_SPEC_CTRL:
 		if (!msr->host_initiated &&
-		    !guest_cpuid_has_ibrs(vcpu))
+		    !guest_cpuid_has_spec_ctrl(vcpu))
 			return 1;
 
 		/* The STIBP bit doesn't fault even if it's not advertised */
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2528,7 +2528,7 @@ static int vmx_get_msr(struct kvm_vcpu *
 		break;
 	case MSR_IA32_SPEC_CTRL:
 		if (!msr_info->host_initiated &&
-		    !guest_cpuid_has_ibrs(vcpu))
+		    !guest_cpuid_has_spec_ctrl(vcpu))
 			return 1;
 
 		msr_info->data = to_vmx(vcpu)->spec_ctrl;
@@ -2633,11 +2633,11 @@ static int vmx_set_msr(struct kvm_vcpu *
 		break;
 	case MSR_IA32_SPEC_CTRL:
 		if (!msr_info->host_initiated &&
-		    !guest_cpuid_has_ibrs(vcpu))
+		    !guest_cpuid_has_spec_ctrl(vcpu))
 			return 1;
 
 		/* The STIBP bit doesn't fault even if it's not advertised */
-		if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP))
+		if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_RDS))
 			return 1;
 
 		vmx->spec_ctrl = data;