KVM: Document that KVM_GET_SUPPORTED_CPUID may return emulated values

Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/Documentation/kvm/api.txt b/Documentation/kvm/api.txt
index 24d6341..b336266 100644
--- a/Documentation/kvm/api.txt
+++ b/Documentation/kvm/api.txt
@@ -1042,8 +1042,9 @@
 entries in the 'entries' array, which is then filled.
 
 The entries returned are the host cpuid as returned by the cpuid instruction,
-with unknown or unsupported features masked out.  The fields in each entry
-are defined as follows:
+with unknown or unsupported features masked out.  Some features (for example,
+x2apic), may not be present in the host cpu, but are exposed by kvm if it can
+emulate them efficiently. The fields in each entry are defined as follows:
 
   function: the eax value used to obtain the entry
   index: the ecx value used to obtain the entry (for entries that are