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@xxxxxxxxxx>
---
Changes from v1:
Updated documentation.
Documentation/virtual/kvm/cpuid.txt | 6 +++++-
arch/x86/kvm/cpuid.c | 2 +-
2 files changed, 6 insertions(+), 2 deletions(-)
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 @@ a guest.
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 9fed5be..eba8345 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -397,7 +397,7 @@ static int do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
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];
--
MST
--
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