On Tue, Aug 7, 2012 at 7:20 PM, Christoffer Dall <c.dall@xxxxxxxxxxxxxxxxxxxxxx> wrote: > On Tue, Aug 7, 2012 at 10:54 AM, Avi Kivity <avi@xxxxxxxxxx> 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. >> 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. > > see git repo: https://github.com/virtualopensystems/linux-kvm-arm/commit/d611960b0745d759e26e77ca47ef3274237e4b65 > or list archive: > https://lists.cs.columbia.edu/pipermail/kvmarm/2012-July/002695.html > >> >> btw, seems there is a needless atomic operation above. May be >> worthwhile to test before clearing. >> >> > (argh unknown gmail keyboard shortcut pressed) you mean in vcpu_load you want to do this instead: if (cpumask_test_cpu(cpu, &vcpu->arch.require_dcache_flush)) { cpumask_clear_cpu(cpu, &vcpu->arch.require_dcache_flush); flush_cache_all(); } ? -Christoffer _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm
