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

[Avi Kivity <avi@qumranet.com>]

Glauber de Oliveira Costa wrote:
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> 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