Re: [Qemu-devel] [PATCH RESEND v2] i386/kvm: add support for KVM_CAP_X86_DISABLE_EXITS

[Paolo Bonzini]

On 17/04/2018 22:59, Eduardo Habkost wrote:
>> +        if (disable_exits) {
>> +            disable_exits &= (KVM_X86_DISABLE_EXITS_MWAIT |
>> +                              KVM_X86_DISABLE_EXITS_HLT |
>> +                              KVM_X86_DISABLE_EXITS_PAUSE);
>> +            if (env->user_features[FEAT_KVM] & KVM_PV_UNHALT) {
>> +                disable_exits &= ~KVM_X86_DISABLE_EXITS_HLT;
>> +            }
>
> In the future, if we decide to enable kvm-pv-unhalt by default,
> should "-cpu ...,kvm-hint-dedicated=on" disable kvm-pv-unhalt
> automatically, or should we require an explicit
> "kvm-hint-dedicated=on,kvm-pv-unhalt=off" option?

It should be automatic.

> For today's defaults, this patch solves the problem, only one
> thing is missing before I give my R-b: we need to clearly
> document what exactly are the consequences and requirements of
> setting kvm-hint-dedicated=on (I'm not sure if the best place for
> this is qemu-options.hx, x86_cpu_list(), or somewhere else).

I don't think we have a good place for this kind of documentation,
unfortunately.  Right now it is mentioned in
Documentation/virtual/kvm/cpuid.txt.

Paolo