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Date: Sun, 15 Jul 2012 19:32:39 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: avi@redhat.com, gleb@redhat.com, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, jan.kiszka@siemens.com
Subject: Re: [PATCH v4 2/3] kvm: KVM_EOIFD, an eventfd for EOIs
Message-ID: <20120715163238.GB17995@redhat.com>
References: <20120713192625.5474.60777.stgit@bling.home>
 <20120713194103.5474.54352.stgit@bling.home>
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On Fri, Jul 13, 2012 at 01:41:05PM -0600, Alex Williamson wrote:
> +static int kvm_assign_eoifd(struct kvm *kvm, struct kvm_eoifd *args)
> +{
> +	struct eventfd_ctx *level_irqfd = NULL, *eventfd = NULL;
> +	struct _eoifd *eoifd = NULL;
> +	struct _irq_source *source = NULL;
> +	unsigned gsi;
> +	int ret;
> +
> +	eventfd = eventfd_ctx_fdget(args->fd);
> +	if (IS_ERR(eventfd)) {
> +		ret = PTR_ERR(eventfd);
> +		goto fail;
> +	}
> +
> +	eoifd = kzalloc(sizeof(*eoifd), GFP_KERNEL);
> +	if (!eoifd) {
> +		ret = -ENOMEM;
> +		goto fail;
> +	}
> +
> +	if (args->flags & KVM_EOIFD_FLAG_LEVEL_IRQFD) {
> +		struct _irqfd *irqfd = _irqfd_fdget_lock(kvm, args->irqfd);
> +		if (IS_ERR(irqfd)) {
> +			ret = PTR_ERR(irqfd);
> +			goto fail;
> +		}
> +
> +		gsi = irqfd->gsi;
> +		level_irqfd = eventfd_ctx_get(irqfd->eventfd);
> +		source = _irq_source_get(irqfd->source);
> +		_irqfd_put_unlock(irqfd);
> +		if (!source) {
> +			ret = -EINVAL;
> +			goto fail;
> +		}
> +	} else {
> +		ret = -EINVAL;
> +		goto fail;
> +	}
> +
> +	INIT_LIST_HEAD(&eoifd->list);
> +	eoifd->kvm = kvm;
> +	eoifd->eventfd = eventfd;
> +	eoifd->source = source;
> +	eoifd->level_irqfd = level_irqfd;
> +	eoifd->notifier.gsi = gsi;
> +	eoifd->notifier.irq_acked = eoifd_event;
> +
> +	mutex_lock(&kvm->eoifds.lock);
> +
> +	list_add_tail(&eoifd->list, &kvm->eoifds.items);

Do we want to disallow multiple eventfds mapping the same irqfd?
No strong opinions but preventing this might make it possible to cache
the callback in the irqfd in the future.

This will also help limit the number of eoifd-s to 1024 GSIs * 32 source ids.
As it is userspace can apparently consume unlimited kernel memory.