Re: [PATCH 1/7] KVM: x86: add SPEC_CTRL and IBPB_SUPPORT accessors

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On 08/01/18 20:08, Paolo Bonzini wrote:
As an interim measure until SPEC_CTRL is supported by upstream
Linux in cpufeatures, add a function that lets vmx.c and svm.c
know whether to save/restore MSR_IA32_SPEC_CTRL.

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
  arch/x86/kvm/cpuid.c |  3 ---
  arch/x86/kvm/cpuid.h | 22 ++++++++++++++++++++++
  2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 8e9a07c557f1..767af697c20c 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -67,9 +67,6 @@ u64 kvm_supported_xcr0(void)

  #define F(x) bit(X86_FEATURE_##x)

-/* These are scattered features in cpufeatures.h. */
-#define KVM_CPUID_BIT_AVX512_4VNNIW     2
-#define KVM_CPUID_BIT_AVX512_4FMAPS     3
  #define KF(x) bit(KVM_CPUID_BIT_##x)

  int kvm_update_cpuid(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index c2cea6651279..8d04ccf177ce 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -155,6 +155,28 @@ static inline int guest_cpuid_stepping(struct kvm_vcpu *vcpu)
  	return x86_stepping(best->eax);
  }

+/* These are scattered features in cpufeatures.h. */
+#define KVM_CPUID_BIT_AVX512_4VNNIW	2
+#define KVM_CPUID_BIT_AVX512_4FMAPS	3
+#define KVM_CPUID_BIT_SPEC_CTRL		26
+#define KVM_CPUID_BIT_STIBP		27
+
+/* CPUID[eax=0x80000008].ebx */
+#define KVM_CPUID_BIT_IBPB_SUPPORT	12
+
+static inline bool cpu_has_spec_ctrl(void)
+{
+	u32 eax, ebx, ecx, edx;
+	cpuid_count(7, 0, &eax, &ebx, &ecx, &edx);
+
+	return edx & bit(KVM_CPUID_BIT_SPEC_CTRL);

Why not just "return cpuid_edx(7) & bit(KVM_CPUID_BIT_SPEC_CTRL);"?
This is also consistent with how cpu_has_ibpb_support() is written.

+}
+
+static inline bool cpu_has_ibpb_support(void)
+{
+	return cpuid_ebx(0x80000008) & bit(KVM_CPUID_BIT_IBPB_SUPPORT);
+}
+
  static inline bool supports_cpuid_fault(struct kvm_vcpu *vcpu)
  {
  	return vcpu->arch.msr_platform_info & MSR_PLATFORM_INFO_CPUID_FAULT;




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