Re: [PATCH 1/2] KVM: Implement default IRQ routing

[Gleb Natapov <gleb@redhat.com>]

On Tue, Sep 17, 2013 at 07:18:40PM +1000, Paul Mackerras wrote:
> This implements a simple way to express the case of IRQ routing where
> there is one in-kernel PIC and the system interrupts (GSIs) are routed
> 1-1 to the corresponding pins of the PIC.  This is expressed by having
> kvm->irq_routing = NULL with a skeleton irq routing entry in the new
> kvm->default_irq_route field.
> 
> This provides a convenient way to provide backwards compatibility when
> adding IRQ routing capability to an existing in-kernel PIC, such as the
> XICS emulation on powerpc.
> 
Why not create simple 1-1 irq routing table? It will take a little bit
more memory, but there will be no need for kvm->irq_routing = NULL
special handling.

> Signed-off-by: Paul Mackerras <paulus@samba.org>
> ---
>  include/linux/kvm_host.h |  1 +
>  virt/kvm/eventfd.c       |  4 ++++
>  virt/kvm/irqchip.c       | 23 ++++++++++++++++++++---
>  3 files changed, 25 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 749bdb1..609f587 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -394,6 +394,7 @@ struct kvm {
>  	 * if configured, irqfds.lock.
>  	 */
>  	struct kvm_irq_routing_table __rcu *irq_routing;
> +	struct kvm_kernel_irq_routing_entry default_irq_route;
>  	struct hlist_head mask_notifier_list;
>  	struct hlist_head irq_ack_notifier_list;
>  #endif
> diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
> index abe4d60..7010cb3 100644
> --- a/virt/kvm/eventfd.c
> +++ b/virt/kvm/eventfd.c
> @@ -272,6 +272,10 @@ static void irqfd_update(struct kvm *kvm, struct _irqfd *irqfd,
>  {
>  	struct kvm_kernel_irq_routing_entry *e;
>  
> +	if (!irq_rt) {
> +		rcu_assign_pointer(irqfd->irq_entry, NULL);
> +		return;
> +	}
>  	if (irqfd->gsi >= irq_rt->nr_rt_entries) {
>  		rcu_assign_pointer(irqfd->irq_entry, NULL);
>  		return;
> diff --git a/virt/kvm/irqchip.c b/virt/kvm/irqchip.c
> index 20dc9e4..ebc2941 100644
> --- a/virt/kvm/irqchip.c
> +++ b/virt/kvm/irqchip.c
> @@ -30,13 +30,24 @@
>  #include <trace/events/kvm.h>
>  #include "irq.h"
>  
> +static inline int pin_to_gsi(struct kvm *kvm, unsigned irqchip, unsigned pin)
> +{
> +	struct kvm_irq_routing_table *rt;
> +	int gsi = pin;
> +
> +	rt = rcu_dereference(kvm->irq_routing);
> +	if (rt)
> +		gsi = rt->chip[irqchip][pin];
> +	return gsi;
> +}
> +
>  bool kvm_irq_has_notifier(struct kvm *kvm, unsigned irqchip, unsigned pin)
>  {
>  	struct kvm_irq_ack_notifier *kian;
>  	int gsi;
>  
>  	rcu_read_lock();
> -	gsi = rcu_dereference(kvm->irq_routing)->chip[irqchip][pin];
> +	gsi = pin_to_gsi(kvm, irqchip, pin);
>  	if (gsi != -1)
>  		hlist_for_each_entry_rcu(kian, &kvm->irq_ack_notifier_list,
>  					 link)
> @@ -59,7 +70,7 @@ void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
>  	trace_kvm_ack_irq(irqchip, pin);
>  
>  	rcu_read_lock();
> -	gsi = rcu_dereference(kvm->irq_routing)->chip[irqchip][pin];
> +	gsi = pin_to_gsi(kvm, irqchip, pin);
>  	if (gsi != -1)
>  		hlist_for_each_entry_rcu(kian, &kvm->irq_ack_notifier_list,
>  					 link)
> @@ -126,7 +137,13 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level,
>  	 */
>  	rcu_read_lock();
>  	irq_rt = rcu_dereference(kvm->irq_routing);
> -	if (irq < irq_rt->nr_rt_entries)
> +	if (!irq_rt) {
> +		if (kvm->default_irq_route.set) {
> +			irq_set[i] = kvm->default_irq_route;
> +			irq_set[i].gsi = irq;
> +			irq_set[i++].irqchip.pin = irq;
> +		}
> +	} else if (irq < irq_rt->nr_rt_entries)
>  		hlist_for_each_entry(e, &irq_rt->map[irq], link)
>  			irq_set[i++] = *e;
>  	rcu_read_unlock();
> -- 
> 1.8.4.rc3
> 
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--
			Gleb.