On 08/07/2012 05:42 PM, Marc Zyngier wrote: > On 07/08/12 15:23, Avi Kivity wrote: >> On 08/07/2012 05:15 PM, Marc Zyngier wrote: >> >>>> vcpu migration is supposed to be transparent. What happens if you >>>> perform the operation locally, then the vcpu is migrated? >>> >>> Migrated as in "moved to another physical CPU"? We have a per-vcpu cpumask >>> indicating which CPU must perform a full cache clean/invalidate, which we >>> test in kvm_arch_vcpu_load(). >>> >> >> How is the cpumask maintained? All cpus which were touched by the vcpu? > > Each time we trap a cache invalidate by set/way (and only these), we > perform it on the the local CPU, and flag all other CPUs to nuke their > own caches if they ever run this vcpu (using the above cpumask). > > Whenever this vcpu is schedule on another CPU, we execute this from > kvm_arch_vcpu_load(): > /* > * Check whether this vcpu requires the cache to be flushed on > * this physical CPU. This is a consequence of doing dcache > * operations by set/way on this vcpu. We do it here to be in > * a non-preemptible section. > */ > if (cpumask_test_and_clear_cpu(cpu, &vcpu->arch.require_dcache_flush)) > flush_cache_all(); /* We'd really want v7_flush_dcache_all() */ > I see. Then you don't need the entire exit path to be non-preemptible. You could, in the invalidate handler, do: preempt_disable() cpumask_setall() cpumask_clear(me) perform local operation preempt_enable() Whether we're migrated before or after, we should be safe. btw, seems there is a needless atomic operation above. May be worthwhile to test before clearing. > >> btw, x86 mostly ignores cache invalidates (an exception is device >> assignment). > > We cannot afford this on ARM when executing an invalidate by set/way. > All the other cache maintenance operations are safe and run on the guest. I see now, thanks for the explanations. -- error compiling committee.c: too many arguments to function _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm
