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

[Marc Zyngier <maz@kernel.org>]

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.