Re: [PATCH] qemu-kvm: Ask kernel about supported svm features

[Avi Kivity <avi@redhat.com>]

On 04/22/2010 03:02 PM, Joerg Roedel wrote:
>>
>>> Signed-off-by: Joerg Roedel<joerg.roedel@amd.com>
>>> ---
>>>   qemu-kvm-x86.c |   14 ++++++++++++--
>>>   1 files changed, 12 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/qemu-kvm-x86.c b/qemu-kvm-x86.c
>>> index 748ff69..6eccd69 100644
>>> --- a/qemu-kvm-x86.c
>>> +++ b/qemu-kvm-x86.c
>>> @@ -1327,8 +1327,18 @@ int kvm_arch_init_vcpu(CPUState *cenv)
>>>       qemu_kvm_cpuid_on_env(&copy);
>>>       limit = copy.regs[R_EAX];
>>>
>>> -    for (i = 0x80000000; i<= limit; ++i)
>>> -	do_cpuid_ent(&cpuid_ent[cpuid_nent++], i, 0,&copy);
>>> +    for (i = 0x80000000; i<= limit; ++i) {
>>> +        do_cpuid_ent(&cpuid_ent[cpuid_nent], i, 0,&copy);
>>> +        switch (i) {
>>> +            case 0x8000000a:
>>> +                cpuid_ent[cpuid_nent].eax = kvm_arch_get_supported_cpuid(cenv, 0x8000000a, R_EAX);
>>> +                cpuid_ent[cpuid_nent].ebx = kvm_arch_get_supported_cpuid(cenv, 0x8000000a, R_EBX);
>>> +                cpuid_ent[cpuid_nent].ebx = kvm_arch_get_supported_cpuid(cenv, 0x8000000a, R_EBX);
>>> +                cpuid_ent[cpuid_nent].edx = kvm_arch_get_supported_cpuid(cenv, 0x8000000a, R_EDX);
>>> +                break;
>>> +        }
>>> +        cpuid_nent += 1;
>>> +    }
>>>        
>> I don't understand why this is different compared to all other cpuid bits.
>>      
> Because for the SVM features we report to the guest we need to ask the
> kernel which of them are supported.

That's true for all cpuid features.

> We can't just take the host-cpuid
> because most of the additional svm features need special emulation in
> the kernel. Or do you think this should better be handled in
> target-i386/cpuid.c?
>    

Yes.  -cpu host should take KVM_GET_SUPPORTED_CPUID output and loop it 
back to the vcpu configuration, others just take the qemu configuration, 
mask it with supported bits, and pass it back (see 
check_features_against_host()).

(need feature names for the bits, too, so you can enable or disable them 
from the command line)

-- 
error compiling committee.c: too many arguments to function