Re: [v5 1/3] KVM: setup empty irq routing when create vm

[Christian Borntraeger]

Am 17.04.26 um 12:19 schrieb Paolo Bonzini:
> On 4/17/26 11:36, Christian Borntraeger wrote:
> > >          irq_rt = srcu_dereference_check(kvm->irq_routing, &kvm- >irq_srcu,
> > >                                          lockdep_is_held(&kvm- >irq_lock));
> > >          if (irq_rt && gsi < irq_rt->nr_rt_entries) {  <---------
> > Hmm, I guess I misread the code and the problem is likely not this.
> > Let me have another look.
>
> It makes sense anyway, together with a similar extra element in
> kvm_set_irq_routing():


Turns out that the bisect was wrong. the increased cpu consumption came from
commit aeb1b22a3ac8e94c791f06f16e921384794771fa ("KVM: Enable halt polling shrink parameter by default")
which kind of makes sense.


@Paolo, shall I do a patch with 0 nr_rt_entries anyway as discussed or shall we
drop this?



> diff --git a/virt/kvm/irqchip.c b/virt/kvm/irqchip.c
> index 462c70621247..c3e4fbbfed94 100644
> --- a/virt/kvm/irqchip.c
> +++ b/virt/kvm/irqchip.c
> @@ -178,11 +178,9 @@ int kvm_set_irq_routing(struct kvm *kvm,
>       for (i = 0; i < nr; ++i) {
>           if (ue[i].gsi >= KVM_MAX_IRQ_ROUTES)
>               return -EINVAL;
> -        nr_rt_entries = max(nr_rt_entries, ue[i].gsi);
> +        nr_rt_entries = max(nr_rt_entries + 1, ue[i].gsi);
>       }
>
> -    nr_rt_entries += 1;
> -
>       new = kzalloc_flex(*new, map, nr_rt_entries, GFP_KERNEL_ACCOUNT);
>       if (!new)
>           return -ENOMEM;
> @@ -246,11 +244,11 @@ int kvm_init_irq_routing(struct kvm *kvm)
>       struct kvm_irq_routing_table *new;
>       int chip_size;
>
> -    new = kzalloc_flex(*new, map, 1, GFP_KERNEL_ACCOUNT);
> +    new = kzalloc_flex(*new, map, 0, GFP_KERNEL_ACCOUNT);
>       if (!new)
>           return -ENOMEM;
>
> -    new->nr_rt_entries = 1;
> +    new->nr_rt_entries = 0;
>
>       chip_size = sizeof(int) * KVM_NR_IRQCHIPS * KVM_IRQCHIP_NUM_PINS;
>       memset(new->chip, -1, chip_size);
>
> Paolo