[PATCH 4.4 57/88] x86/KVM/VMX: Expose SPEC_CTRL Bit(2) to the guest

Greg Kroah-Hartman
2018-12-14T12:18:15Z

From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

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>
---
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
@@ -364,7 +364,7 @@ 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(SPEC_CTRL_SSBD) | 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
@@ -170,7 +170,7 @@ 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;

@@ -178,7 +178,7 @@ 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_SPEC_CTRL_SSBD)));
}

static inline bool guest_cpuid_has_arch_capabilities(struct kvm_vcpu *vcpu)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -3090,7 +3090,7 @@ 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;
@@ -3171,7 +3171,7 @@ 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
@@ -2861,7 +2861,7 @@ 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;
@@ -2973,11 +2973,11 @@ 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_SSBD))
return 1;

vmx->spec_ctrl = data;