KVM: fix cpuid eax for KVM leaf
cpuid eax should return the max leaf so that
guests can find out the valid range.
This matches Xen et al.
Update documentation to match.
Tested with -cpu host.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt
index 8820685..83afe65 100644
--- a/Documentation/virtual/kvm/cpuid.txt
+++ b/Documentation/virtual/kvm/cpuid.txt
@@ -10,11 +10,15 @@
KVM cpuid functions are:
function: KVM_CPUID_SIGNATURE (0x40000000)
-returns : eax = 0,
+returns : eax = 0x40000001,
ebx = 0x4b4d564b,
ecx = 0x564b4d56,
edx = 0x4d.
Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM".
+The value in eax corresponds to the maximum cpuid function present in this leaf,
+and will be updated if more functions are added in the future.
+Note also that old hosts set eax value to 0x0. This should
+be interpreted as if the value was 0x40000001.
This function queries the presence of KVM cpuid leafs.
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index c2134b8..7df1c6d 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -398,7 +398,7 @@
case KVM_CPUID_SIGNATURE: {
char signature[12] = "KVMKVMKVM\0\0";
u32 *sigptr = (u32 *)signature;
- entry->eax = 0;
+ entry->eax = KVM_CPUID_FEATURES;
entry->ebx = sigptr[0];
entry->ecx = sigptr[1];
entry->edx = sigptr[2];