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

[Wanpeng Li <kernellwp@gmail.com>]

2018-04-18 4:59 GMT+08:00 Eduardo Habkost <ehabkost@redhat.com>:
> On Tue, Apr 17, 2018 at 01:24:15AM -0700, Wanpeng Li wrote:
[.../...]
>>
>> +    if (env->features[FEAT_KVM_HINTS] & KVM_HINTS_DEDICATED) {
>> +        int disable_exits = kvm_check_extension(cs->kvm_state, KVM_CAP_X86_DISABLE_EXITS);
>> +
>> +        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?
>
> 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).

What's your opinion, Paolo?

Regards,
Wanpeng Li