Re: [PATCH v4 07/11] KVM: arm/arm64: vgic: Allow HW interrupts to be queued to a guest

[Andre Przywara <andre.przywara@arm.com>]

Salut Marc,

I know that this patch is already merged, but ....

On 07/08/15 16:45, Marc Zyngier wrote:
> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> index 51c9900..9d009d2 100644
...
> @@ -1364,6 +1397,39 @@ static bool vgic_process_maintenance(struct kvm_vcpu *vcpu)
>  	return level_pending;
>  }
>  
> +/*
> + * Save the physical active state, and reset it to inactive.
> + *
> + * Return 1 if HW interrupt went from active to inactive, and 0 otherwise.
> + */
> +static int vgic_sync_hwirq(struct kvm_vcpu *vcpu, struct vgic_lr vlr)
> +{
> +	struct irq_phys_map *map;
> +	int ret;
> +
> +	if (!(vlr.state & LR_HW))
> +		return 0;
> +
> +	map = vgic_irq_map_search(vcpu, vlr.irq);
> +	BUG_ON(!map || !map->active);
> +
> +	ret = irq_get_irqchip_state(map->irq,
> +				    IRQCHIP_STATE_ACTIVE,
> +				    &map->active);
> +
> +	WARN_ON(ret);
> +
> +	if (map->active) {
> +		ret = irq_set_irqchip_state(map->irq,
> +					    IRQCHIP_STATE_ACTIVE,
> +					    false);
> +		WARN_ON(ret);
> +		return 0;
> +	}
> +
> +	return 1;
> +}
> +
>  /* Sync back the VGIC state after a guest run */
>  static void __kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu)
>  {
> @@ -1378,14 +1444,31 @@ static void __kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu)
>  	elrsr = vgic_get_elrsr(vcpu);
>  	elrsr_ptr = u64_to_bitmask(&elrsr);
>  
> -	/* Clear mappings for empty LRs */
> -	for_each_set_bit(lr, elrsr_ptr, vgic->nr_lr) {
> +	/* Deal with HW interrupts, and clear mappings for empty LRs */
> +	for (lr = 0; lr < vgic->nr_lr; lr++) {
>  		struct vgic_lr vlr;
>  
> -		if (!test_and_clear_bit(lr, vgic_cpu->lr_used))
> +		if (!test_bit(lr, vgic_cpu->lr_used))
>  			continue;
>  
>  		vlr = vgic_get_lr(vcpu, lr);
> +		if (vgic_sync_hwirq(vcpu, vlr)) {
> +			/*
> +			 * So this is a HW interrupt that the guest
> +			 * EOI-ed. Clean the LR state and allow the
> +			 * interrupt to be sampled again.
> +			 */
> +			vlr.state = 0;
> +			vlr.hwirq = 0;
> +			vgic_set_lr(vcpu, lr, vlr);
> +			vgic_irq_clear_queued(vcpu, vlr.irq);

Isn't this line altering common VGIC state without holding the lock?
Eric removed the coarse dist->lock around the whole
__kvm_vgic_sync_hwstate() function, we take it now in
vgic_process_maintenance(), but don't hold it here AFAICT.
As long as we are only dealing with private timer IRQs this is probably
not a problem, but the IRQ number could be a SPI as well, right?

Cheers,
Andre.

> +			set_bit(lr, elrsr_ptr);
> +		}
> +
> +		if (!test_bit(lr, elrsr_ptr))
> +			continue;
> +
> +		clear_bit(lr, vgic_cpu->lr_used);
>  
>  		BUG_ON(vlr.irq >= dist->nr_irqs);
>  		vgic_cpu->vgic_irq_lr_map[vlr.irq] = LR_EMPTY;
>