Re: [PATCH 10/10] KVM: Adds support for halting in the kernel

["Gregory Haskins" <ghaskins-Et1tbQHTxzrQT0dZR+AlfA@public.gmane.org>]

>>> On Thu, May 24, 2007 at  4:29 AM, in message <46554CFF.9040101-atKUWr5tajBWk0Htik3J/w@public.gmane.org>,
Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org> wrote: 
> Gregory Haskins wrote:
>> Halting in userspace requires a relatively cumbersome mechanism to signal 
> the
>> halted VCPU.  Implementing halt in kernel should be relatively straight
>> forward and it eliminates the need for the signaling
>>
>>  /*
>> + * The vCPU has executed a HLT instruction with in- kernel mode enabled.
>> + */
>> +static int kvm_vcpu_kern_halt(struct kvm_vcpu *vcpu, struct kvm_run 
> *kvm_run)
>> +{
>> +	DECLARE_WAITQUEUE(wait, current);
>> +	sigset_t sigblocked, sigsaved;
>> +	int r = 1;
>> +
>> +	/*
>> +	 * Unmask all signals while we wait
>> +	 */
>> +	memset(&sigblocked, 0, sizeof(sigblocked));
>> +	sigprocmask(SIG_SETMASK, &sigblocked, &sigsved);
>>   
> 
> We have a specialized signal mask for the kernel, and it is already in 
> effect here.  See KVM_SET_SIGNAL_MASK.
> 

KVM_SET_SIGNAL_MASK is precisely what I was trying to counteract ;).  Basically I was thinking that userspace could have set some arbitrary mask that would be in effect at this time.  My justification for unmasking everything is two fold:  

1) I think I really want *any* signal to kick the HLT, so I temporarily unmask everything while halted.

2) Old userspace halting would not have the SET_SIGNAL_MASK set at the time either, since we would have restored the original mask before returning to userspace.

That being said, I am not an expert here so I may have got it wrong.  Please advise.

-Greg

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