Re: [PATCH v2 4/6] kvm: Extend irqfd to support level interrupts

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jun 26, 2012 at 11:09:46PM -0600, Alex Williamson wrote:
> In order to inject an interrupt from an external source using an
> irqfd, we need to allocate a new irq_source_id.  This allows us to
> assert and (later) de-assert an interrupt line independently from
> users of KVM_IRQ_LINE and avoid lost interrupts.
> 
> We also add what may appear like a bit of excessive infrastructure
> around an object for storing this irq_source_id.  However, notice
> that we only provide a way to assert the interrupt here.  A follow-on
> interface will make use of the same irq_source_id to allow de-assert.
> 
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> ---
> 
>  Documentation/virtual/kvm/api.txt |    5 ++
>  arch/x86/kvm/x86.c                |    1 
>  include/linux/kvm.h               |    3 +
>  virt/kvm/eventfd.c                |   95 +++++++++++++++++++++++++++++++++++--
>  4 files changed, 99 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index ea9edce..b216709 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -1981,6 +1981,11 @@ the guest using the specified gsi pin.  The irqfd is removed using
>  the KVM_IRQFD_FLAG_DEASSIGN flag, specifying both kvm_irqfd.fd
>  and kvm_irqfd.gsi.
>  
> +With KVM_IRQFD_FLAG_LEVEL KVM_IRQFD allocates a new IRQ source ID for
> +the requested irqfd.  This is necessary to share level triggered
> +interrupts with those injected through KVM_IRQ_LINE.  IRQFDs created
> +with KVM_IRQFD_FLAG_LEVEL must also set this flag when de-assiging.
> +KVM_IRQFD_FLAG_LEVEL support is indicated by KVM_CAP_IRQFD_LEVEL.

Note that if my patch removing auto-deassert gets accepted,
this is not needed at all: we can just look at the GSI
to see if it's level or edge.

>  
>  5. The kvm_run structure
>  ------------------------
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a01a424..80bed07 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2148,6 +2148,7 @@ int kvm_dev_ioctl_check_extension(long ext)
>  	case KVM_CAP_GET_TSC_KHZ:
>  	case KVM_CAP_PCI_2_3:
>  	case KVM_CAP_KVMCLOCK_CTRL:
> +	case KVM_CAP_IRQFD_LEVEL:
>  		r = 1;
>  		break;
>  	case KVM_CAP_COALESCED_MMIO:
> diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> index 2ce09aa..b2e6e4f 100644
> --- a/include/linux/kvm.h
> +++ b/include/linux/kvm.h
> @@ -618,6 +618,7 @@ struct kvm_ppc_smmu_info {
>  #define KVM_CAP_PPC_GET_SMMU_INFO 78
>  #define KVM_CAP_S390_COW 79
>  #define KVM_CAP_PPC_ALLOC_HTAB 80
> +#define KVM_CAP_IRQFD_LEVEL 81
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> @@ -683,6 +684,8 @@ struct kvm_xen_hvm_config {
>  #endif
>  
>  #define KVM_IRQFD_FLAG_DEASSIGN (1 << 0)
> +/* Available with KVM_CAP_IRQFD_LEVEL */
> +#define KVM_IRQFD_FLAG_LEVEL (1 << 1)
>  
>  struct kvm_irqfd {
>  	__u32 fd;
> diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
> index 7d7e2aa..18cc284 100644
> --- a/virt/kvm/eventfd.c
> +++ b/virt/kvm/eventfd.c
> @@ -36,6 +36,64 @@
>  #include "iodev.h"
>  
>  /*
> + * An irq_source_id can be created from KVM_IRQFD for level interrupt
> + * injections and shared with other interfaces for EOI or de-assert.
> + * Create an object with reference counting to make it easy to use.
> + */
> +struct _irq_source {
> +	int id;
> +	struct kvm *kvm;
> +	struct kref kref;
> +};
> +
> +static void release_irq_source(struct kref *kref)
> +{
> +	struct _irq_source *source;
> +
> +	source = container_of(kref, struct _irq_source, kref);
> +
> +	kvm_free_irq_source_id(source->kvm, source->id);
> +	kfree(source);
> +}
> +
> +static void put_irq_source(struct _irq_source *source)
> +{
> +	if (source)
> +		kref_put(&source->kref, release_irq_source);
> +}
> +
> +static struct _irq_source *__attribute__ ((used)) /* white lie for now */
> +get_irq_source(struct _irq_source *source)
> +{
> +	if (source)
> +		kref_get(&source->kref);
> +
> +	return source;
> +}
> +
> +static struct _irq_source *new_irq_source(struct kvm *kvm)
> +{
> +	struct _irq_source *source;
> +	int id;
> +
> +	source = kzalloc(sizeof(*source), GFP_KERNEL);
> +	if (!source)
> +		return ERR_PTR(-ENOMEM);
> +
> +	id = kvm_request_irq_source_id(kvm);
> +	if (id < 0) {
> +		kfree(source);
> +		return ERR_PTR(id);
> +	}
> +
> +	kref_init(&source->kref);
> +	source->kvm = kvm;
> +	source->id = id;
> +
> +	return source;
> +}
> +
> +/*
>   * --------------------------------------------------------------------
>   * irqfd: Allows an fd to be used to inject an interrupt to the guest
>   *
> @@ -52,6 +110,7 @@ struct _irqfd {
>  	/* Used for level IRQ fast-path */
>  	int gsi;
>  	struct work_struct inject;
> +	struct _irq_source *source;
>  	/* Used for setup/shutdown */
>  	struct eventfd_ctx *eventfd;
>  	struct list_head list;
> @@ -62,7 +121,7 @@ struct _irqfd {
>  static struct workqueue_struct *irqfd_cleanup_wq;
>  
>  static void
> -irqfd_inject(struct work_struct *work)
> +irqfd_inject_edge(struct work_struct *work)
>  {
>  	struct _irqfd *irqfd = container_of(work, struct _irqfd, inject);
>  	struct kvm *kvm = irqfd->kvm;
> @@ -71,6 +130,14 @@ irqfd_inject(struct work_struct *work)
>  	kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0);
>  }
>  
> +static void
> +irqfd_inject_level(struct work_struct *work)
> +{
> +	struct _irqfd *irqfd = container_of(work, struct _irqfd, inject);
> +
> +	kvm_set_irq(irqfd->kvm, irqfd->source->id, irqfd->gsi, 1);
> +}
> +
>  /*
>   * Race-free decouple logic (ordering is critical)
>   */
> @@ -96,6 +163,9 @@ irqfd_shutdown(struct work_struct *work)
>  	 * It is now safe to release the object's resources
>  	 */
>  	eventfd_ctx_put(irqfd->eventfd);
> +
> +	put_irq_source(irqfd->source);
> +
>  	kfree(irqfd);
>  }
>  
> @@ -214,7 +284,19 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
>  	irqfd->kvm = kvm;
>  	irqfd->gsi = args->gsi;
>  	INIT_LIST_HEAD(&irqfd->list);
> -	INIT_WORK(&irqfd->inject, irqfd_inject);
> +
> +	if (args->flags & KVM_IRQFD_FLAG_LEVEL) {
> +		irqfd->source = new_irq_source(kvm);
> +		if (IS_ERR(irqfd->source)) {
> +			ret = PTR_ERR(irqfd->source);
> +			irqfd->source = NULL;
> +			goto fail;
> +		}
> +
> +		INIT_WORK(&irqfd->inject, irqfd_inject_level);
> +	} else
> +		INIT_WORK(&irqfd->inject, irqfd_inject_edge);
> +
>  	INIT_WORK(&irqfd->shutdown, irqfd_shutdown);
>  
>  	file = eventfd_fget(args->fd);
> @@ -279,9 +361,10 @@ fail:
>  	if (eventfd && !IS_ERR(eventfd))
>  		eventfd_ctx_put(eventfd);
>  
> -	if (!IS_ERR(file))
> +	if (file && !IS_ERR(file))
>  		fput(file);
>  
> +	put_irq_source(irqfd->source);
>  	kfree(irqfd);
>  	return ret;
>  }
> @@ -302,6 +385,7 @@ kvm_irqfd_deassign(struct kvm *kvm, struct kvm_irqfd *args)
>  {
>  	struct _irqfd *irqfd, *tmp;
>  	struct eventfd_ctx *eventfd;
> +	bool is_level = (args->flags & KVM_IRQFD_FLAG_LEVEL) != 0;
>  
>  	eventfd = eventfd_ctx_fdget(args->fd);
>  	if (IS_ERR(eventfd))
> @@ -310,7 +394,8 @@ kvm_irqfd_deassign(struct kvm *kvm, struct kvm_irqfd *args)
>  	spin_lock_irq(&kvm->irqfds.lock);
>  
>  	list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds.items, list) {
> -		if (irqfd->eventfd == eventfd && irqfd->gsi == args->gsi) {
> +		if (irqfd->eventfd == eventfd && irqfd->gsi == args->gsi &&
> +		    is_level == (irqfd->source != NULL)) {
>  			/*
>  			 * This rcu_assign_pointer is needed for when
>  			 * another thread calls kvm_irq_routing_update before
> @@ -340,7 +425,7 @@ kvm_irqfd_deassign(struct kvm *kvm, struct kvm_irqfd *args)
>  int
>  kvm_irqfd(struct kvm *kvm, struct kvm_irqfd *args)
>  {
> -	if (args->flags & ~KVM_IRQFD_FLAG_DEASSIGN)
> +	if (args->flags & ~(KVM_IRQFD_FLAG_DEASSIGN | KVM_IRQFD_FLAG_LEVEL))
>  		return -EINVAL;
>  
>  	if (args->flags & KVM_IRQFD_FLAG_DEASSIGN)