On Wed, May 13, 2015 at 10:04:53AM +0200, Paolo Bonzini wrote:
>
>
> On 13/05/2015 08:12, Jan Kiszka wrote:
> >> +void kvm_scan_ioapic_routes(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap)
> >> +{
> >> + struct kvm *kvm = vcpu->kvm;
> >> + struct kvm_kernel_irq_routing_entry *entry;
> >> + struct kvm_irq_routing_table *table;
> >> + u32 i, nr_rt_entries;
> >> +
> >> + mutex_lock(&kvm->irq_lock);
>
> This only needs irq_srcu protection, not irq_lock, so the lookup cost
> becomes much smaller (all CPUs can proceed in parallel).
>
> You would need to put an smp_mb here, to ensure that irq_routing is read
> after KVM_SCAN_IOAPIC is cleared. You can introduce
> smb_mb__after_srcu_read_lock in order to elide it.
>
> The matching memory barrier would be a smp_mb__before_atomic in
> kvm_make_scan_ioapic_request.
>
Makes sense, I'll update this for the next iteration.
Steve
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