Re: [PATCH 2/5 V5] Add functions to check if the host has stoppedthe vm

[Eric B Munson]

On Wed, 14 Dec 2011, Avi Kivity wrote:

> On 12/14/2011 07:11 PM, Eric B Munson wrote:
> > > > > 
> > > > > If I understand (please correct me if this is wrong) because this is only
> > > > > called from the watchdog, which disables preemption, we should be protected
> > > > > from something else writing to these flags.
> > > >
> > > > The host can write, but in that case race is harmless.
> > > 
> > > Why is it harmless?  You don't know what's in those other flags.
> > > 
> > > -- 
> > > error compiling committee.c: too many arguments to function
> > > 
> >
> > Currently there is only one other flag in this byte (PVCLOCK_TSC_STABLE_BIT)
> > and it isset once in kvmclock_init().  It is highly unlikely that the vm will
> > be stopped during this init and have the flag clobbered.  After the tsc stable
> > bit is written in the init, the field is read only outside of the guest paused
> > code.
> 
> Let's not lay minefields for us later to step into.  Making this a
> cpu-local atomic (irq safe but not smp safe) is simple and easy,
> somehting like __this_cpu_and().
> 
> -- 
> error compiling committee.c: too many arguments to function
> 

Fair enough, I will add this to V7.

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