Re: [PATCH 16/32] KVM: arm64: gic: Introduce irq_queue and set_pending_state to irq_ops

[Marc Zyngier <maz@kernel.org>]

On Fri, 12 Dec 2025 15:22:40 +0000,
Sascha Bischoff <Sascha.Bischoff@arm.com> wrote:
> 
> There are times when the default behaviour of vgic_queue_irq_unlock is
> undesirable. This is because some GICs, such a GICv5 which is the main
> driver for this change, handle the majority of the interrupt lifecycle
> in hardware. In this case, there is no need for a per-VCPU AP list as
> the interrupt can be made pending directly. This is done either via
> the ICH_PPI_x_EL2 registers for PPIs, or with the VDPEND system
> instruction for SPIs and LPIs.
> 
> The queue_irq_unlock function is made overridable using a new function
> pointer in struct irq_ops. In kvm_vgic_inject_irq,
> vgic_queue_irq_unlock is overridden if the function pointer is
> non-null.
> 
> Additionally, a new function is added via a function pointer -
> set_pending_state. The intent is for this to be used to directly set
> the pending state in hardware.
> 
> Both of these new irq_ops are unused in this change - it is purely
> providing the infrastructure itself. The subsequent PPI injection
> changes provide a demonstration of their usage.
> 
> Signed-off-by: Sascha Bischoff <sascha.bischoff@arm.com>
> ---
>  arch/arm64/kvm/vgic/vgic.c |  9 ++++++++-
>  include/kvm/arm_vgic.h     | 15 +++++++++++++++
>  2 files changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
> index 1fe3dcc997860..fc01c6d07fe62 100644
> --- a/arch/arm64/kvm/vgic/vgic.c
> +++ b/arch/arm64/kvm/vgic/vgic.c
> @@ -547,7 +547,14 @@ int kvm_vgic_inject_irq(struct kvm *kvm, struct kvm_vcpu *vcpu,
>  	else
>  		irq->pending_latch = true;
>  
> -	vgic_queue_irq_unlock(kvm, irq, flags);
> +	if (irq->ops && irq->ops->set_pending_state)
> +		WARN_ON_ONCE(!irq->ops->set_pending_state(vcpu, irq));
> +
> +	if (irq->ops && irq->ops->queue_irq_unlock)
> +		WARN_ON_ONCE(!irq->ops->queue_irq_unlock(kvm, irq, flags));
> +	else
> +		vgic_queue_irq_unlock(kvm, irq, flags);

I find it slightly dubious to WARN() in one case but not the other.

More importantly, why isn't the per-irq queue_unlock operation tucked
into the vgic_queue_irq_unlock() primitive? We have 16 call sites for
this function, and it is odd that only the injection primitive would
benefit from this.

Thanks,

	M.

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