Re: [PATCH 04/15] KVM: arm64: vgic-its: Walk the LPI xarray in vgic_copy_lpi_list()

Oliver Upton
2024-01-25T09:24:38Z

On Thu, Jan 25, 2024 at 09:15:30AM +0000, Marc Zyngier wrote:
> On Wed, 24 Jan 2024 20:48:58 +0000,
> Oliver Upton <oliver.upton@linux.dev> wrote:
> >
> > Start iterating the LPI xarray in anticipation of removing the LPI
> > linked-list.
> >
> > Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
> > ---
> > arch/arm64/kvm/vgic/vgic-its.c | 7 ++++++-
> > 1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c
> > index f152d670113f..a2d95a279798 100644
> > --- a/arch/arm64/kvm/vgic/vgic-its.c
> > +++ b/arch/arm64/kvm/vgic/vgic-its.c
> > @@ -332,6 +332,7 @@ static int update_lpi_config(struct kvm *kvm, struct vgic_irq *irq,
> > int vgic_copy_lpi_list(struct kvm *kvm, struct kvm_vcpu *vcpu, u32 **intid_ptr)
> > {
> > struct vgic_dist *dist = &kvm->arch.vgic;
> > + XA_STATE(xas, &dist->lpi_xa, 0);
>
> Why 0? LPIs start at 8192 (aka GIC_LPI_OFFSET), so it'd probably make
> sense to use that.

Just being lazy!

> > struct vgic_irq *irq;
> > unsigned long flags;
> > u32 *intids;
> > @@ -350,7 +351,9 @@ int vgic_copy_lpi_list(struct kvm *kvm, struct kvm_vcpu *vcpu, u32 **intid_ptr)
> > return -ENOMEM;
> >
> > raw_spin_lock_irqsave(&dist->lpi_list_lock, flags);
> > - list_for_each_entry(irq, &dist->lpi_list_head, lpi_list) {
> > + rcu_read_lock();
> > +
> > + xas_for_each(&xas, irq, U32_MAX) {
>
> Similar thing: we advertise 16 bits of ID space (described as
> INTERRUPT_ID_BITS_ITS), so capping at that level would make it more
> understandable.

See above. But completely agree, this is much more readable when it
matches the the actual ID space.

--
Thanks,
Oliver