Re: [Qemu-devel] [PATCH 1/2] target-i386: Fix default Hypervisor level for accel=kvm.

[Eduardo Habkost]

On Tue, Sep 18, 2012 at 10:49:52AM -0400, Don Slutz wrote:
> From http://lkml.indiana.edu/hypermail/linux/kernel/1205.0/00100.html
> EAX should be KVM_CPUID_FEATURES (0x40000001) not 0.
> ---
>  target-i386/kvm.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> index 761a9b1..0c9f5dd 100644
> --- a/target-i386/kvm.c
> +++ b/target-i386/kvm.c
> @@ -392,7 +392,7 @@ int kvm_arch_init_vcpu(CPUX86State *env)
>      c->function = KVM_CPUID_SIGNATURE;
>      if (env->cpuid_hv_level == 0) {
>          memcpy(signature, "KVMKVMKVM\0\0\0", 12);
> -        c->eax = 0;
> +        c->eax = KVM_CPUID_FEATURES;

This makes the CPUID bits to suddenly change, when live-migrating to a
newer QEMU version.

Strictly speaking, this is never supposed to happen, but... on both
cases the meaning of the bits are the same (0 is documented as
equivalent to KVM_CPUID_FEATURES) and probably the guest will look at
them only once on boot. Do we really want to add migration-compatibility
code for this?


>          c->ebx = signature[0];
>          c->ecx = signature[1];
>          c->edx = signature[2];
> -- 
> 1.7.1
> 

-- 
Eduardo