Re: [Qemu-devel] [PATCH v3 2/3] kvm: Add support to KVM_GET_MSR_FEATURE_INDEX_LIST and KVM_GET_MSRS system ioctl

[Paolo Bonzini]

On 23/08/2018 19:11, Eduardo Habkost wrote:
>>> We don't want QEMU to refuse to run if the kernel doesn't have
>>> KVM_CAP_GET_MSR_FEATURES.  We can treat missing capability as
>>> equivalent to returning an empty list of MSRs.
>> Yes. I'll let caller (kvm_arch_init) ignore the return value but a
>> simple warning.
> Warnings tend to be ignored and are generally a sign that QEMU
> isn't doing the right thing.  Sometimes we have no choice, but I
> don't think that's the case here.
> 
> As far as I can see, we have only two possibilities here:
> 1) The host can run a VM that behaves exactly as requested on the
>    command-line (no warning required).
> 2) The host can't run the requested configuration (fatal error,
>    not a warning).

Right, but if KVM_CAP_GET_MSR_FEATURES is not available I guess you can
assume the MSRs to be zero for everything except "-cpu host".

Paolo