Re: [RFC 3/3] vfio: Share the KVM instance with Vdmabuf

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

On Tue, 19 Jan 2021 00:28:12 -0800
Vivek Kasireddy <vivek.kasireddy@intel.com> wrote:

> Getting a copy of the KVM instance is necessary for mapping Guest
> pages in the Host.
> 
> TODO: Instead of invoking the symbol directly, there needs to be a
> better way of getting a copy of the KVM instance probably by using
> other notifiers. However, currently, KVM shares its instance only
> with VFIO and therefore we are compelled to bind the passthrough'd
> device to vfio-pci.

Yeah, this is a bad solution, sorry, vfio is not going to gratuitously
call out to vhost to share a kvm pointer.  I'd prefer to get rid of
vfio having any knowledge or visibility of the kvm pointer.  Thanks,

Alex
 
> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
> ---
>  drivers/vfio/vfio.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index 4ad8a35667a7..9fb11b1ad3cd 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -2213,11 +2213,20 @@ static int vfio_unregister_iommu_notifier(struct vfio_group *group,
>  	return ret;
>  }
>  
> +extern void vhost_vdmabuf_get_kvm(unsigned long action, void *data);
>  void vfio_group_set_kvm(struct vfio_group *group, struct kvm *kvm)
>  {
> +	void (*fn)(unsigned long, void *);
> +
>  	group->kvm = kvm;
>  	blocking_notifier_call_chain(&group->notifier,
>  				VFIO_GROUP_NOTIFY_SET_KVM, kvm);
> +
> +	fn = symbol_get(vhost_vdmabuf_get_kvm);
> +	if (fn) {
> +		fn(VFIO_GROUP_NOTIFY_SET_KVM, kvm);
> +		symbol_put(vhost_vdmabuf_get_kvm);
> +	}
>  }
>  EXPORT_SYMBOL_GPL(vfio_group_set_kvm);
>  

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