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Commit 57c22e5f authored by Michael S. Tsirkin's avatar Michael S. Tsirkin Committed by Avi Kivity
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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: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent e726b1bd

Documentation/virtual/kvm/cpuid.txt

+5 −1
Original line number Diff line number Diff line
@@ -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.

arch/x86/kvm/cpuid.c

+1 −1
Original line number Diff line number Diff line
@@ -398,7 +398,7 @@ 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];