On 07/08/12 15:54, Avi Kivity wrote: > 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. Christoffer already found a solution for this, which is pretty much what you suggest: > You could, in the invalidate handler, do: > > preempt_disable() > cpumask_setall() > cpumask_clear(me) > perform local operation Here, we have to test if we're still on the CPU that caused the trap, and do a full cache nuke if we've been migrated. > 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. Sure. M. -- Jazz is not dead. It just smells funny... _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm
