From mboxrd@z Thu Jan  1 00:00:00 1970
From: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Subject: Re: [v3 4/5] vfio: implement APIs to set/put kvm to/from vfio group
Date: Wed, 9 Nov 2016 21:06:23 +0800
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Cc: Alex Williamson <alex.williamson@redhat.com>, kwankhede@nvidia.com,
        cjia@nvidia.com, kevin.tian@intel.com, kvm@vger.kernel.org
To: Jike Song <jike.song@intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>
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On 11/09/2016 08:49 PM, Jike Song wrote:

> +void vfio_group_attach_kvm(struct vfio_group *group, struct kvm *kvm,
> +		void (*fn)(struct kvm *))
> +{
> +	mutex_lock(&group->udata.lock);

This lock is needed, please see below.

> +
> +	fn(kvm);
> +	blocking_notifier_call_chain(&group->udata.notifier,
> +				VFIO_GROUP_NOTIFY_ATTACH_KVM, kvm);

As this is a callback before KVM releases its last refcount, i do not
think vendor driver need to get additional KVM refcount.