On Sat, Jul 28, 2018 at 11:07:33AM +0200, Mike Galbraith wrote:
>
> b103cc3f10c0 ("KVM: arm/arm64: Avoid timer save/restore in vcpu entry/exit")
> requires vgic_irq.irq_lock be converted to raw_spinlock_t.
>
> Problem: kvm_preempt_ops.sched_in = kvm_sched_in;
> kvm_sched_in()
> kvm_arch_vcpu_load()
> kvm_timer_vcpu_load() <- b103cc3f10c0 addition
> kvm_timer_vcpu_load_gic()
> kvm_vgic_map_is_active()
> spin_lock_irqsave(&irq->irq_lock, flags);
>
> Quoting virt/kvm/arm/vgic/vgic.c, locking order is...
>
> kvm->lock (mutex)
> its->cmd_lock (mutex)
> its->its_lock (mutex)
> vgic_cpu->ap_list_lock must be taken with IRQs disabled
> kvm->lpi_list_lock must be taken with IRQs disabled
> vgic_irq->irq_lock must be taken with IRQs disabled
>
> ...meaning vgic_dist.lpi_list_lock and vgic_cpu.ap_list_lock must be
> converted as well.
The thing missing from the Changelog is the analysis that all the work
done under these locks is indeed properly bounded and cannot cause
excessive latencies.
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