[PATCH 3.16 019/192] kvm: x86: Guest BNDCFGS requires guest MPX support

[Ben Hutchings]

3.16.49-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jim Mattson <jmattson@xxxxxxxxxx>

commit 4439af9f911ae0243ffe4e2dfc12bace49605d8b upstream.

The BNDCFGS MSR should only be exposed to the guest if the guest
supports MPX. (cf. the TSC_AUX MSR and RDTSCP.)

Fixes: 0dd376e709975779 ("KVM: x86: add MSR_IA32_BNDCFGS to msrs_to_save")
Change-Id: I3ad7c01bda616715137ceac878f3fa7e66b6b387
Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
Signed-off-by: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/x86/kvm/cpuid.h | 8 ++++++++
 arch/x86/kvm/vmx.c   | 4 ++--
 2 files changed, 10 insertions(+), 2 deletions(-)

--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -95,4 +95,13 @@ static inline bool guest_cpuid_has_gbpag
 	best = kvm_find_cpuid_entry(vcpu, 0x80000001, 0);
 	return best && (best->edx & bit(X86_FEATURE_GBPAGES));
 }
+
+static inline bool guest_cpuid_has_mpx(struct kvm_vcpu *vcpu)
+{
+	struct kvm_cpuid_entry2 *best;
+
+	best = kvm_find_cpuid_entry(vcpu, 7, 0);
+	return best && (best->ebx & bit(X86_FEATURE_MPX));
+}
+
 #endif
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2514,7 +2514,7 @@ static int vmx_get_msr(struct kvm_vcpu *
 		data = vmcs_readl(GUEST_SYSENTER_ESP);
 		break;
 	case MSR_IA32_BNDCFGS:
-		if (!vmx_mpx_supported())
+		if (!vmx_mpx_supported() || !guest_cpuid_has_mpx(vcpu))
 			return 1;
 		data = vmcs_read64(GUEST_BNDCFGS);
 		break;
@@ -2587,7 +2587,7 @@ static int vmx_set_msr(struct kvm_vcpu *
 		vmcs_writel(GUEST_SYSENTER_ESP, data);
 		break;
 	case MSR_IA32_BNDCFGS:
-		if (!vmx_mpx_supported())
+		if (!vmx_mpx_supported() || !guest_cpuid_has_mpx(vcpu))
 			return 1;
 		vmcs_write64(GUEST_BNDCFGS, data);
 		break;