KVM: cpuid: mask more bits in leaf 0xd and subleaves

- EAX=0Dh, ECX=1: output registers EBX/ECX/EDX are reserved.

- EAX=0Dh, ECX>1: output register ECX bit 0 is clear for all the CPUID
leaves we support, because variable "supported" comes from XCR0 and not
XSS.  Bits above 0 are reserved, so ECX is overall zero.  Output register
EDX is reserved.

Source: Intel Architecture Instruction Set Extensions Programming
Reference, ref. number 319433-022

Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Tested-by: Wanpeng Li <wanpeng.li@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/cpuid.c

@@ -482,8 +482,14 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 					entry[i].ebx =
 						xstate_required_size(supported,
 								     true);
-			} else if (entry[i].eax == 0 || !(supported & mask))
-				continue;
+			} else {
+				if (entry[i].eax == 0 || !(supported & mask))
+					continue;
+				if (WARN_ON_ONCE(entry[i].ecx & 1))
+					continue;
+			}
+			entry[i].ecx = 0;
+			entry[i].edx = 0;
 			entry[i].flags |=
 			       KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
 			++*nent;