Re: [kvm-devel] [PATCH 2/3] kvmclock - the host part.

Avi Kivity
2007-11-13T14:49:05Z

Glauber de Oliveira Costa wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Dong, Eddie escreveu:
>
>>> +static void kvm_write_guest_time(struct kvm_vcpu *vcpu) +{
>>> + struct timespec ts;
>>> + int r;
>>> +
>>> + if (!vcpu->clock_gpa)
>>> + return;
>>> +
>>> + /* Updates version to the next odd number, indicating
>>> we're writing */
>>> + vcpu->hv_clock.version++;
>>> + kvm_write_guest(vcpu->kvm, vcpu->clock_gpa,
>>> &vcpu->hv_clock, PAGE_SIZE);
>>> +
>>> + kvm_get_msr(vcpu, MSR_IA32_TIME_STAMP_COUNTER,
>>> + &vcpu->hv_clock.last_tsc);
>>> +
>>> + ktime_get_ts(&ts);
>>>
>> Do we need to disable preemption here?
>>
> After thinking for a little while, you are theoretically right.
> In the current state, we could even be preempted between all operations
> ;-) Maybe after avi's suggestion of moving the call to it it will end up
> in a preempt safe region, but anyway, it's safer to add the preempt
> markers here.
> I'll put it in next version, thanks
>
>

Well, you can't kvm_write_guest() with preemption enabled.

preempt notifiers to the rescue! We have a callout during preemption,
so you can just zero out a flag there, and when we're scheduled again
retry the whole thing.

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