[PATCH 5.10 598/717] KVM: x86: reinstate vendor-agnostic check on SPEC_CTRL cpuid bits

Greg Kroah-Hartman
2020-12-28T14:42:52Z

From: Paolo Bonzini <pbonzini@redhat.com>

commit 39485ed95d6b83b62fa75c06c2c4d33992e0d971 upstream.

Until commit e7c587da1252 ("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: e7c587da1252 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kvm/cpuid.h | 14 ++++++++++++++
arch/x86/kvm/svm/svm.c | 14 ++++----------
arch/x86/kvm/vmx/vmx.c | 8 ++++----
3 files changed, 22 insertions(+), 14 deletions(-)

--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -264,6 +264,20 @@ static inline int guest_cpuid_stepping(s
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;
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2543,10 +2543,7 @@ static int svm_get_msr(struct kvm_vcpu *
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;
@@ -2630,10 +2627,7 @@ static int svm_set_msr(struct kvm_vcpu *
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))
@@ -2658,12 +2652,12 @@ static int svm_set_msr(struct kvm_vcpu *
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;
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1826,7 +1826,7 @@ static int vmx_get_msr(struct kvm_vcpu *
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 *
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 *
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;