Re: [PATCH 2/3] Improve DEC handling

[Alexander Graf <agraf-l3A5Bk7waGM@public.gmane.org>]

Hollis Blanchard wrote:
> On Mon, Dec 21, 2009 at 10:13 AM, Hollis Blanchard
> <hollis-yUx37fBWTUITNcAmw9vGhQ@public.gmane.org> wrote:
>   
>>  void kvmppc_emulate_dec(struct kvm_vcpu *vcpu)
>>  {
>>        unsigned long dec_nsec;
>>
>>        pr_debug("mtDEC: %x\n", vcpu->arch.dec);
>>  #ifdef CONFIG_PPC64
>>        /* POWER4+ triggers a dec interrupt if the value is < 0 */
>>        if (vcpu->arch.dec & 0x80000000) {
>>                hrtimer_try_to_cancel(&vcpu->arch.dec_timer);
>>                kvmppc_core_queue_dec(vcpu);
>> +               /* keep queuing interrupts until guest clears high MSR bit */
>> +               hrtimer_start(&vcpu->arch.dec_timer, ktime_set(0, 100),
>> +                             HRTIMER_MODE_REL);
>>                return;
>>        }
>>  #endif
>>     
>
> Of course, removing the hardcoded 100-ns timer would be better, and
> indeed we can do that. What we *really* want is to key off of MSR[EE]
> changes (there's no point in queuing anything until then).

Yes. mtmsr with EE=1 triggers a #VMEXIT which then goes off into a VM
entry which on entering checks that the DEC interrupt is still active
and fires it.

> So why not
> move your "AGGRESSIVE_DEC" check into Book 3S's kvmppc_set_msr()?
>   

The idea was to get rid of AGGRESSIVE_DEC :-).

Alex