[Bug 77271] CPUID Leaf 0x40000000 return 0 in eax

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=77271

Alex Williamson <alex.williamson@redhat.com> changed:

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                 CC|                            |alex.williamson@redhat.com

--- Comment #1 from Alex Williamson <alex.williamson@redhat.com> ---
Further up in cpuid.txt is the statement:

"This is not always guaranteed to work, since userspace can
mask-out some, or even all KVM-related cpuid features before launching
a guest."

Which is exactly what is happening here.  QEMU sets eax = 0 for this leaf:

target-i386/kvm.c
    memcpy(signature, "KVMKVMKVM\0\0\0", 12);
    c = &cpuid_data.entries[cpuid_i++];
    c->function = KVM_CPUID_SIGNATURE | kvm_base;
    c->eax = 0;
    c->ebx = signature[0];
    c->ecx = signature[1];
    c->edx = signature[2];

So I don't think there's a bug here.

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