Dong, Eddie wrote: >>> >>> 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. >> >> > > The preemption issue is within following code which need to be done in a > short enough period. > > + kvm_get_msr(vcpu, MSR_IA32_TIME_STAMP_COUNTER, > + &vcpu->hv_clock.last_tsc); > + > + ktime_get_ts(&ts); > + vcpu->hv_clock.now_ns = ts.tv_nsec + (NSEC_PER_SEC * > (u64)ts.tv_sec); > + vcpu->hv_clock.wc_sec = get_seconds(); > > I am even thinking we have to disable interrupt between these lines, > otherwise > guest wall clock may see backward time source when calculating the > delta TSC since last vcpu->hv_clock.now_ns update. >
That's true. While we do need to handle vcpu migration and descheduling, the code sequence you note needs to be as atomic as possible. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
