x86/KVM/VMX: Expose SPEC_CTRL Bit(2) to the guest

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@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
[dwmw2: Handle 4.9 guest CPUID differences, rename
        guest_cpu_has_ibrs() → guest_cpu_has_spec_ctrl()]
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 4.4: Update feature bit name]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 0ab72a8387d43a62a7043b51dd9a17c4cf32d86b..6b20e0a823da762fe0cc8210cdfe08d72d5ba1e7 100644 (file)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -364,7 +364,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 
        /* cpuid 7.0.edx*/
        const u32 kvm_cpuid_7_0_edx_x86_features =
-               F(SPEC_CTRL) | F(ARCH_CAPABILITIES);
+               F(SPEC_CTRL) | F(SPEC_CTRL_SSBD) | F(ARCH_CAPABILITIES);
 
        /* all calls to cpuid_count() should be made on the same cpu */
        get_cpu();

diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index 7f74d7e18a012e3676e5c93fd81df00b9b2d2314..31ff5d2d05369c3ad0ce6f63aeb161cbb2cdbfc8 100644 (file)
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -170,7 +170,7 @@ static inline bool guest_cpuid_has_ibpb(struct kvm_vcpu *vcpu)
        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;
 
@@ -178,7 +178,7 @@ static inline bool guest_cpuid_has_ibrs(struct kvm_vcpu *vcpu)
        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_SPEC_CTRL_SSBD)));
 }
 
 static inline bool guest_cpuid_has_arch_capabilities(struct kvm_vcpu *vcpu)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index f863035927684cec6cacc813d0e4f50872485f5e..9b3ac8c54a59db06b1691d56b3bb022388b1aa57 100644 (file)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -3090,7 +3090,7 @@ 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_ibrs(vcpu))
+                   !guest_cpuid_has_spec_ctrl(vcpu))
                        return 1;
 
                msr_info->data = svm->spec_ctrl;
@@ -3171,7 +3171,7 @@ 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_ibrs(vcpu))
+                   !guest_cpuid_has_spec_ctrl(vcpu))
                        return 1;
 
                /* The STIBP bit doesn't fault even if it's not advertised */

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 0fffd247037bad3400b98384a83987b33b43c964..ea2e36d855690bb4c0e6e08d33b53e1c3fb98079 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2861,7 +2861,7 @@ 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_ibrs(vcpu))
+                   !guest_cpuid_has_spec_ctrl(vcpu))
                        return 1;
 
                msr_info->data = to_vmx(vcpu)->spec_ctrl;
@@ -2973,11 +2973,11 @@ 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_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_SSBD))
                        return 1;
 
                vmx->spec_ctrl = data;