Messages in this thread | | | Date | Fri, 01 May 2015 09:39:35 -0400 | From | Boris Ostrovsky <> | Subject | Re: [Xen-devel] [PATCH v2 1/4] xen/events: Clear cpu_evtchn_mask before resuming |
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On 05/01/2015 06:46 AM, David Vrabel wrote: > On 29/04/15 22:10, Boris Ostrovsky wrote: >> When a guest is resumed, the hypervisor may change event channel >> assignments. If this happens and the guest uses 2-level events it >> is possible for the interrupt to be claimed by wrong VCPU since >> cpu_evtchn_mask bits may be stale. This can happen even though >> evtchn_2l_bind_to_cpu() attempts to clear old bits: irq_info that >> is passed in is not necessarily the original one (from pre-migration >> times) but instead is freshly allocated during resume and so any >> information about which CPU the channel was bound to is lost. >> >> Thus we should clear the mask during resume. >> >> We also need to make sure that bits for xenstore and console channels >> are set when these two subsystems are resumed. While rebind_evtchn_irq() >> (which is invoked for both of them on a resume) calls irq_set_affinity(), >> the latter will in fact postpone setting affinity until handling the >> interrupt. But because cpu_evtchn_mask will have bits for these two >> cleared we won't be able to take the interrupt. >> >> With that in mind, we need to bind those two channels explicitly in >> rebind_evtchn_irq(). We will keep irq_set_affinity() so that we have a >> pass through generic irq affinity code later, in case something needs >> to be updated there as well. >> >> (Also replace cpumask_of(0) with cpumask_of(info->cpu) in >> rebind_evtchn_irq(): it should be set to zero in preceding >> xen_irq_info_evtchn_setup().) > [...] >> @@ -1279,8 +1280,16 @@ void rebind_evtchn_irq(int evtchn, int irq) >> >> mutex_unlock(&irq_mapping_update_lock); >> >> - /* new event channels are always bound to cpu 0 */ >> - irq_set_affinity(irq, cpumask_of(0)); >> + bind_vcpu.port = evtchn; >> + bind_vcpu.vcpu = info->cpu; >> + if (HYPERVISOR_event_channel_op(EVTCHNOP_bind_vcpu, &bind_vcpu) == 0) >> + bind_evtchn_to_cpu(evtchn, info->cpu); > Isn't the hypercall is unnecessary since this is a new event channel > it's already bound to VCPU 0 and info->cpu == 0? > > I think only the bind_evtchn_to_cpu() call is needed here.
True. However, I added the hypercall here to make the routine independent of what happens in other parts (hypervisor binding new channels to cpu0, xen_irq_info_evtchn_setup() initializing to zero, etc.). This way, if either of these two change in the future (unlikely, but possible) this routine will still work as expected.
That's why I also replaced cpumask_of(0) with cpumask_of(info->cpu) in irq_set_affinity() call.
-boris
> > If you agree I can remove the hypercall and apply this series. > >> + else >> + pr_warn("Failed binding port %d to cpu %d\n", >> + evtchn, info->cpu); >> + >> + /* This will be deferred until interrupt is processed */ >> + irq_set_affinity(irq, cpumask_of(info->cpu)); > David >
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