Re: [v7 3/3] kvm: set/clear kvm to/from vfio_group when group add/delete

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 22 Nov 2016 14:09:33 +0800
Jike Song <jike.song@intel.com> wrote:

> Sometimes users need to be aware when a vfio_group attaches to a
> KVM or detaches from it. KVM already calls get/put method from vfio to
> manipulate the vfio_group reference, it can notify vfio_group in
> a similar way.
> 
> Cc: Alex Williamson <alex.williamson@redhat.com>
> Cc: Kirti Wankhede <kwankhede@nvidia.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Xiao Guangrong <guangrong.xiao@linux.intel.com>
> Signed-off-by: Jike Song <jike.song@intel.com>
> ---
>  virt/kvm/vfio.c | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
> 
> diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
> index 1dd087d..ea5b4bb 100644
> --- a/virt/kvm/vfio.c
> +++ b/virt/kvm/vfio.c
> @@ -60,6 +60,32 @@ static void kvm_vfio_group_put_external_user(struct vfio_group *vfio_group)
>  	symbol_put(vfio_group_put_external_user);
>  }
>  
> +static void kvm_vfio_group_set_kvm(struct vfio_group *group, struct kvm *kvm)
> +{
> +	void (*fn)(struct vfio_group *, struct kvm *);
> +
> +	fn = symbol_get(vfio_group_set_kvm);
> +	if (!fn)
> +		return;
> +
> +	fn(group, kvm);
> +
> +	symbol_put(vfio_group_set_kvm);
> +}
> +
> +static void kvm_vfio_group_clear_kvm(struct vfio_group *group, struct kvm *kvm)
> +{
> +	void (*fn)(struct vfio_group *, struct kvm *);
> +
> +	fn = symbol_get(vfio_group_set_kvm);
> +	if (!fn)
> +		return;
> +
> +	fn(group, NULL);
> +
> +	symbol_put(vfio_group_set_kvm);
> +}


Why do we need this function?  Can't we simply call
kvm_vfio_group_set_kvm(vfio_group, NULL)?  Not to mention that the
struct kvm arg is unused here otherwise.

> +
>  static bool kvm_vfio_group_is_coherent(struct vfio_group *vfio_group)
>  {
>  	long (*fn)(struct vfio_group *, unsigned long);
> @@ -155,6 +181,8 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
>  		list_add_tail(&kvg->node, &kv->group_list);
>  		kvg->vfio_group = vfio_group;
>  
> +		kvm_vfio_group_set_kvm(vfio_group, dev->kvm);
> +
>  		kvm_arch_start_assignment(dev->kvm);
>  
>  		mutex_unlock(&kv->lock);
> @@ -196,6 +224,8 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
>  
>  		mutex_unlock(&kv->lock);
>  
> +		kvm_vfio_group_clear_kvm(vfio_group, dev->kvm);
> +


Why did we set_kvm within kv->lock, but clear it outside of kv->lock?
I'm not sure kv->lock is particularly relevant to us but we might as
well be consistent.

>  		kvm_vfio_group_put_external_user(vfio_group);
>  
>  		kvm_vfio_update_coherency(dev);
> @@ -240,6 +270,7 @@ static void kvm_vfio_destroy(struct kvm_device *dev)
>  	struct kvm_vfio_group *kvg, *tmp;
>  
>  	list_for_each_entry_safe(kvg, tmp, &kv->group_list, node) {
> +		kvm_vfio_group_clear_kvm(kvg->vfio_group, dev->kvm);
>  		kvm_vfio_group_put_external_user(kvg->vfio_group);
>  		list_del(&kvg->node);
>  		kfree(kvg);