KVM: x86: reinstate vendor-agnostic check on SPEC_CTRL cpuid bits

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>

1 files changed, 14 insertions, 0 deletions

diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index f7a6e8f83783..dc921d76e42e 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -264,6 +264,20 @@ static inline int guest_cpuid_stepping(struct kvm_vcpu *vcpu)
 	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;