[PULL 1/1] target/i386: disable VMX features if nested=0

[Paolo Bonzini <pbonzini@redhat.com>]

From: Yang Zhong <yang.zhong@intel.com>

If kvm does not support VMX feature by nested=0, the kvm_vmx_basic
can't get the right value from MSR_IA32_VMX_BASIC register, which
make qemu coredump when qemu do KVM_SET_MSRS.

The coredump info:
error: failed to set MSR 0x480 to 0x0
kvm_put_msrs: Assertion `ret == cpu->kvm_msr_buf->nmsrs' failed.

Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Message-Id: <20191206071111.12128-1-yang.zhong@intel.com>
Reported-by: Catherine Ho <catherine.hecx@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 target/i386/kvm.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index bf1655645b..1d10046a6c 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -2572,6 +2572,14 @@ static void kvm_msr_entry_add_vmx(X86CPU *cpu, FeatureWordArray f)
     uint64_t kvm_vmx_basic =
         kvm_arch_get_supported_msr_feature(kvm_state,
                                            MSR_IA32_VMX_BASIC);
+
+    if (!kvm_vmx_basic) {
+        /* If the kernel doesn't support VMX feature (kvm_intel.nested=0),
+         * then kvm_vmx_basic will be 0 and KVM_SET_MSR will fail.
+         */
+        return;
+    }
+
     uint64_t kvm_vmx_misc =
         kvm_arch_get_supported_msr_feature(kvm_state,
                                            MSR_IA32_VMX_MISC);
-- 
2.21.0