On Wednesday 17 November 2010 22:01:41 Avi Kivity wrote:
> On 11/15/2010 11:15 AM, Sheng Yang wrote:
> > We need to query the entry later.
> >
> > +int kvm_get_irq_routing_entry(struct kvm *kvm, int gsi,
> > + struct kvm_kernel_irq_routing_entry *entry)
> > +{
> > + int count = 0;
> > + struct kvm_kernel_irq_routing_entry *ei = NULL;
> > + struct kvm_irq_routing_table *irq_rt;
> > + struct hlist_node *n;
> > +
> > + rcu_read_lock();
> > + irq_rt = rcu_dereference(kvm->irq_routing);
> > + if (gsi< irq_rt->nr_rt_entries)
> > + hlist_for_each_entry(ei, n,&irq_rt->map[gsi], link)
> > + count++;
> > + if (count == 1)
> > + *entry = *ei;
> > + rcu_read_unlock();
> > +
> > + return (count != 1);
> > +}
> > +
>
> Not good form to rely on ei being valid after the loop.
>
> I guess this is only useful for msi? Need to document it.
May can be used for others later, it's somehow generic. Where should I document
it?
>
> *entry may be stale after rcu_read_unlock(). Is this a problem?
I suppose not. All MSI-X MMIO accessing would be executed without delay, so no re-
order issue would happen. If the guest is reading and writing the field at the same
time(from two cpus), it should got some kinds of sync method for itself - or it
may not care what's the reading result(like the one after msix_mask_irq()).
--
regards
Yang, Sheng
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