[PATCH] i386/kvm: mask MSR_IA32_BNDCFGS if MPX is not enabled in guest cpuid

[Haozhong Zhang <haozhong.zhang@xxxxxxxxx>]

Otherwise, QEMU on a host with MPX support will try to set guest
MSR_IA32_BNDCFGS although guest MPX is not enabled, and result in
abort.

For example,
   qemu-system-x86_64 -enable-kvm -cpu qemu64,-mpx ...
aborts with messages:
   qemu-system-x86_64: error: failed to set MSR 0xd90 to 0x0
   qemu-system-x86_64: /root/qemu.git/target/i386/kvm.c:1832: kvm_put_msrs: Assertion `ret == cpu->kvm_msr_buf->nmsrs' failed

Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
---
 target/i386/kvm.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index ee36502789..7b3a310a31 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -943,6 +943,11 @@ int kvm_arch_init_vcpu(CPUState *cs)
         has_msr_mcg_ext_ctl = has_msr_feature_control = true;
     }
 
+    if (has_msr_bndcfgs) {
+        c = cpuid_find_entry(&cpuid_data.cpuid, 7, 0);
+        has_msr_bndcfgs = c && (c->ebx & CPUID_7_0_EBX_MPX);
+    }
+
     if (!env->user_tsc_khz) {
         if ((env->features[FEAT_8000_0007_EDX] & CPUID_APM_INVTSC) &&
             invtsc_mig_blocker == NULL) {
-- 
2.11.0