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

Marc Zyngier
2024-01-25T09:15:33Z

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.

> 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.

> if (i == irq_count)
> break;
> /* We don't need to "get" the IRQ, as we hold the list lock. */
> @@ -358,6 +361,8 @@ int vgic_copy_lpi_list(struct kvm *kvm, struct kvm_vcpu *vcpu, u32 **intid_ptr)
> continue;
> intids[i++] = irq->intid;
> }
> +
> + rcu_read_unlock();
> raw_spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
>
> *intid_ptr = intids;

Thanks,

M.

--
Without deviation from the norm, progress is not possible.