Re: [PATCH v5 3/4] kvm: Create kvm_clear_irq()

[Michael S. Tsirkin]

On Mon, Jul 16, 2012 at 02:34:03PM -0600, Alex Williamson wrote:
> This is an alternative to kvm_set_irq(,,,0) which returns the previous
> assertion state of the interrupt and does nothing if it isn't changed.
> 
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> ---
> 
>  include/linux/kvm_host.h |    3 ++
>  virt/kvm/irq_comm.c      |   78 ++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 81 insertions(+)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index a7661c0..6c168f1 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -219,6 +219,8 @@ struct kvm_kernel_irq_routing_entry {
>  	u32 type;
>  	int (*set)(struct kvm_kernel_irq_routing_entry *e,
>  		   struct kvm *kvm, int irq_source_id, int level);
> +	int (*clear)(struct kvm_kernel_irq_routing_entry *e,
> +		     struct kvm *kvm, int irq_source_id);
>  	union {
>  		struct {
>  			unsigned irqchip;
> @@ -629,6 +631,7 @@ void kvm_get_intr_delivery_bitmask(struct kvm_ioapic *ioapic,
>  				   unsigned long *deliver_bitmask);
>  #endif
>  int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level);
> +int kvm_clear_irq(struct kvm *kvm, int irq_source_id, u32 irq);
>  int kvm_set_msi(struct kvm_kernel_irq_routing_entry *irq_entry, struct kvm *kvm,
>  		int irq_source_id, int level);
>  void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin);
> diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
> index 5afb431..76e8f22 100644
> --- a/virt/kvm/irq_comm.c
> +++ b/virt/kvm/irq_comm.c
> @@ -68,6 +68,42 @@ static int kvm_set_ioapic_irq(struct kvm_kernel_irq_routing_entry *e,
>  	return kvm_ioapic_set_irq(ioapic, e->irqchip.pin, level);
>  }
>  
> +static inline int kvm_clear_irq_line_state(unsigned long *irq_state,
> +					    int irq_source_id)
> +{
> +	return !!test_and_clear_bit(irq_source_id, irq_state);
> +}
> +
> +static int kvm_clear_pic_irq(struct kvm_kernel_irq_routing_entry *e,
> +			     struct kvm *kvm, int irq_source_id)
> +{
> +#ifdef CONFIG_X86
> +	struct kvm_pic *pic = pic_irqchip(kvm);
> +	int level = kvm_clear_irq_line_state(&pic->irq_states[e->irqchip.pin],
> +					     irq_source_id);
> +	if (level)
> +		kvm_pic_set_irq(pic, e->irqchip.pin,
> +				!!pic->irq_states[e->irqchip.pin]);
> +	return level;

I think I begin to understand: if (level) checks it was previously set,
and then we clear if needed? I think it's worthwhile to rename
level to orig_level and rewrite as:

	if (orig_level && !pic->irq_states[e->irqchip.pin])
		kvm_pic_set_irq(pic, e->irqchip.pin, 0);

This both makes the logic clear without need for comments and
saves some cycles on pic in case nothing actually changed.

> +#else
> +	return -1;
> +#endif
> +}
> +
> +static int kvm_clear_ioapic_irq(struct kvm_kernel_irq_routing_entry *e,
> +				struct kvm *kvm, int irq_source_id)
> +{
> +	struct kvm_ioapic *ioapic = kvm->arch.vioapic;
> +	int level;
> +
> +	level = kvm_clear_irq_line_state(&ioapic->irq_states[e->irqchip.pin],
> +					 irq_source_id);
> +	if (level)
> +		kvm_ioapic_set_irq(ioapic, e->irqchip.pin,
> +				   !!ioapic->irq_states[e->irqchip.pin]);
> +	return level;
> +}
> +
>  inline static bool kvm_is_dm_lowest_prio(struct kvm_lapic_irq *irq)
>  {
>  #ifdef CONFIG_IA64
> @@ -190,6 +226,45 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level)
>  	return ret;
>  }
>  
> +/*
> + * Return value:
> + *  < 0   Error
> + *  = 0   Interrupt was not set, did nothing
> + *  > 0   Interrupt was pending, cleared
> + */
> +int kvm_clear_irq(struct kvm *kvm, int irq_source_id, u32 irq)
> +{
> +	struct kvm_kernel_irq_routing_entry *e, irq_set[KVM_NR_IRQCHIPS];
> +	int ret = -EINVAL, i = 0;
> +	struct kvm_irq_routing_table *irq_rt;
> +	struct hlist_node *n;
> +
> +	/* Not possible to detect if the guest uses the PIC or the
> +	 * IOAPIC.  So clear the bit in both. The guest will ignore
> +	 * writes to the unused one.
> +	 */
> +	rcu_read_lock();
> +	irq_rt = rcu_dereference(kvm->irq_routing);
> +	if (irq < irq_rt->nr_rt_entries)
> +		hlist_for_each_entry(e, n, &irq_rt->map[irq], link)
> +			irq_set[i++] = *e;
> +	rcu_read_unlock();
> +
> +	while (i--) {
> +		int r = -EINVAL;
> +
> +		if (irq_set[i].clear)
> +			r = irq_set[i].clear(&irq_set[i], kvm, irq_source_id);
> +
> +		if (r < 0)
> +			continue;
> +
> +		ret = r + ((ret < 0) ? 0 : ret);
> +	}
> +
> +	return ret;
> +}
> +
>  void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
>  {
>  	struct kvm_irq_ack_notifier *kian;
> @@ -344,16 +419,19 @@ static int setup_routing_entry(struct kvm_irq_routing_table *rt,
>  		switch (ue->u.irqchip.irqchip) {
>  		case KVM_IRQCHIP_PIC_MASTER:
>  			e->set = kvm_set_pic_irq;
> +			e->clear = kvm_clear_pic_irq;
>  			max_pin = 16;
>  			break;
>  		case KVM_IRQCHIP_PIC_SLAVE:
>  			e->set = kvm_set_pic_irq;
> +			e->clear = kvm_clear_pic_irq;
>  			max_pin = 16;
>  			delta = 8;
>  			break;
>  		case KVM_IRQCHIP_IOAPIC:
>  			max_pin = KVM_IOAPIC_NUM_PINS;
>  			e->set = kvm_set_ioapic_irq;
> +			e->clear = kvm_clear_ioapic_irq;
>  			break;
>  		default:
>  			goto out;
--
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