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

[Don Slutz <Don@CloudSwitch.Com>]

On 09/18/12 11:05, Eduardo Habkost wrote:
> 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?
>
My vote would be no; because this should be ok and the tests that I know 
of are all at boot time.  I will look into adding 
migration-compatibility.  I also do not have any direct need for this 
change, it just looked like the right thing to do.
>>           c->ebx = signature[0];
>>           c->ecx = signature[1];
>>           c->edx = signature[2];
>> -- 
>> 1.7.1
>>