On Wed, 14 Dec 2011, Avi Kivity wrote:

On 12/14/2011 07:11 PM, Eric B Munson wrote:

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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.