KVM: x86: export paravirtual cpuid flags in KVM_GET_SUPPORTED_CPUID

Right now, we were using individual KVM_CAP entities to communicate
userspace about which cpuids we support. This is suboptimal, since it
generates a delay between the feature arriving in the host, and
being available at the guest.

A much better mechanism is to list para features in KVM_GET_SUPPORTED_CPUID.
This makes userspace automatically aware of what we provide. And if we
ever add a new cpuid bit in the future, we have to do that again,
which create some complexity and delay in feature adoption.
Signed-off-by: Glauber Costa <glommer@redhat.com>
Acked-by: Zachary Amsden <zamsden@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/x86.c

@@ -1972,6 +1972,23 @@ static void do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 		}
 		break;
 	}
+	case KVM_CPUID_SIGNATURE: {
+		char signature[12] = "KVMKVMKVM\0\0";
+		u32 *sigptr = (u32 *)signature;
+		entry->eax = 0;
+		entry->ebx = sigptr[0];
+		entry->ecx = sigptr[1];
+		entry->edx = sigptr[2];
+		break;
+	}
+	case KVM_CPUID_FEATURES:
+		entry->eax = (1 << KVM_FEATURE_CLOCKSOURCE) |
+			     (1 << KVM_FEATURE_NOP_IO_DELAY) |
+			     (1 << KVM_FEATURE_CLOCKSOURCE2);
+		entry->ebx = 0;
+		entry->ecx = 0;
+		entry->edx = 0;
+		break;
 	case 0x80000000:
 		entry->eax = min(entry->eax, 0x8000001a);
 		break;
@@ -2018,6 +2035,23 @@ static int kvm_dev_ioctl_get_supported_cpuid(struct kvm_cpuid2 *cpuid,
 	for (func = 0x80000001; func <= limit && nent < cpuid->nent; ++func)
 		do_cpuid_ent(&cpuid_entries[nent], func, 0,
 			     &nent, cpuid->nent);
+
+
+
+	r = -E2BIG;
+	if (nent >= cpuid->nent)
+		goto out_free;
+
+	do_cpuid_ent(&cpuid_entries[nent], KVM_CPUID_SIGNATURE, 0, &nent,
+		     cpuid->nent);
+
+	r = -E2BIG;
+	if (nent >= cpuid->nent)
+		goto out_free;
+
+	do_cpuid_ent(&cpuid_entries[nent], KVM_CPUID_FEATURES, 0, &nent,
+		     cpuid->nent);
+
 	r = -E2BIG;
 	if (nent >= cpuid->nent)
 		goto out_free;