KVM guest: make kvm_para_available() check hypervisor bit reading cpuid leaf

This cpuid range does not exist on real HW and Intel spec says that
"Information returned for highest basic information leaf" will be
returned. Not very well defined.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index 99c4bbe..a7a7a94 100644 (file)
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -178,14 +178,16 @@ static inline int kvm_para_available(void)
        unsigned int eax, ebx, ecx, edx;
        char signature[13];
 
-       cpuid(KVM_CPUID_SIGNATURE, &eax, &ebx, &ecx, &edx);
-       memcpy(signature + 0, &ebx, 4);
-       memcpy(signature + 4, &ecx, 4);
-       memcpy(signature + 8, &edx, 4);
-       signature[12] = 0;
-
-       if (strcmp(signature, "KVMKVMKVM") == 0)
-               return 1;
+       if (cpu_has_hypervisor) {
+               cpuid(KVM_CPUID_SIGNATURE, &eax, &ebx, &ecx, &edx);
+               memcpy(signature + 0, &ebx, 4);
+               memcpy(signature + 4, &ecx, 4);
+               memcpy(signature + 8, &edx, 4);
+               signature[12] = 0;
+
+               if (strcmp(signature, "KVMKVMKVM") == 0)
+                       return 1;
+       }
 
        return 0;
 }