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SubjectRe: [KVM PATCH v6 4/4] KVM: add irqfd DEASSIGN feature
On Mon, Jun 29, 2009 at 11:44:20AM -0400, Gregory Haskins wrote:
> DEASSIGN allows us to optionally disassociate an IRQFD from its underlying
> eventfd without destroying the eventfd in the process. This is useful
> for conditions like live-migration which may have an eventfd associated
> with a device and an IRQFD. We need to be able to decouple the guest
> from the event source while not perturbing the event source itself.
>
> Signed-off-by: Gregory Haskins <ghaskins@novell.com>
> CC: Michael S. Tsirkin <mst@redhat.com>

Very happy to see this feature back. ACK.

> ---
>
> include/linux/kvm.h | 2 ++
> virt/kvm/eventfd.c | 46 ++++++++++++++++++++++++++++++++++++++++++++--
> 2 files changed, 46 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> index 38ff31e..6710518 100644
> --- a/include/linux/kvm.h
> +++ b/include/linux/kvm.h
> @@ -490,6 +490,8 @@ struct kvm_x86_mce {
> };
> #endif
>
> +#define KVM_IRQFD_FLAG_DEASSIGN (1 << 0)
> +
> struct kvm_irqfd {
> __u32 fd;
> __u32 gsi;
> diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
> index 76ad125..409d9e1 100644
> --- a/virt/kvm/eventfd.c
> +++ b/virt/kvm/eventfd.c
> @@ -152,8 +152,8 @@ irqfd_ptable_queue_proc(struct file *file, wait_queue_head_t *wqh,
> add_wait_queue(wqh, &irqfd->wait);
> }
>
> -int
> -kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags)
> +static int
> +kvm_irqfd_assign(struct kvm *kvm, int fd, int gsi)
> {
> struct _irqfd *irqfd;
> struct file *file = NULL;
> @@ -233,6 +233,48 @@ kvm_irqfd_init(struct kvm *kvm)
> }
>
> /*
> + * shutdown any irqfd's that match fd+gsi
> + */
> +static int
> +kvm_irqfd_deassign(struct kvm *kvm, int fd, int gsi)
> +{
> + struct _irqfd *irqfd, *tmp;
> + struct eventfd_ctx *eventfd;
> +
> + eventfd = eventfd_ctx_fdget(fd);
> + if (IS_ERR(eventfd))
> + return PTR_ERR(eventfd);
> +
> + spin_lock_irq(&kvm->irqfds.lock);
> +
> + list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds.items, list) {
> + if (irqfd->eventfd == eventfd && irqfd->gsi == gsi)
> + irqfd_deactivate(irqfd);
> + }
> +
> + spin_unlock_irq(&kvm->irqfds.lock);
> + eventfd_ctx_put(eventfd);
> +
> + /*
> + * Block until we know all outstanding shutdown jobs have completed
> + * so that we guarantee there will not be any more interrupts on this
> + * gsi once this deassign function returns.
> + */
> + flush_workqueue(irqfd_cleanup_wq);
> +
> + return 0;
> +}
> +
> +int
> +kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags)
> +{
> + if (flags & KVM_IRQFD_FLAG_DEASSIGN)
> + return kvm_irqfd_deassign(kvm, fd, gsi);
> +
> + return kvm_irqfd_assign(kvm, fd, gsi);
> +}
> +
> +/*
> * This function is called as the kvm VM fd is being released. Shutdown all
> * irqfds that still remain open
> */


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