linux-kernel - Re: [PATCH v9 04/12] vfio iommu: Add support for mediated devices

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Date:   Fri, 21 Oct 2016 08:36:02 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Jike Song <jike.song@...el.com>
Cc:     Kirti Wankhede <kwankhede@...dia.com>, pbonzini@...hat.com,
        kraxel@...hat.com, cjia@...dia.com, qemu-devel@...gnu.org,
        kvm@...r.kernel.org, kevin.tian@...el.com,
        bjsdjshi@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 04/12] vfio iommu: Add support for mediated devices

On Fri, 21 Oct 2016 15:49:07 +0800
Jike Song <jike.song@...el.com> wrote:

> On 10/18/2016 05:22 AM, Kirti Wankhede wrote:
> > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> > index 2ba19424e4a1..5d67058a611d 100644
> > --- a/drivers/vfio/vfio_iommu_type1.c
> > +++ b/drivers/vfio/vfio_iommu_type1.c  
> [snip]
> >  static int vfio_iommu_type1_attach_group(void *iommu_data,
> >  					 struct iommu_group *iommu_group)
> >  {
> >  	struct vfio_iommu *iommu = iommu_data;
> > -	struct vfio_group *group, *g;
> > +	struct vfio_group *group;
> >  	struct vfio_domain *domain, *d;
> >  	struct bus_type *bus = NULL;
> >  	int ret;
> > @@ -746,10 +1136,14 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
> >  	mutex_lock(&iommu->lock);
> >  
> >  	list_for_each_entry(d, &iommu->domain_list, next) {
> > -		list_for_each_entry(g, &d->group_list, next) {
> > -			if (g->iommu_group != iommu_group)
> > -				continue;
> > +		if (find_iommu_group(d, iommu_group)) {
> > +			mutex_unlock(&iommu->lock);
> > +			return -EINVAL;
> > +		}
> > +	}
> >  
> > +	if (iommu->local_domain) {
> > +		if (find_iommu_group(iommu->local_domain, iommu_group)) {
> >  			mutex_unlock(&iommu->lock);
> >  			return -EINVAL;
> >  		}
> > @@ -769,6 +1163,30 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
> >  	if (ret)
> >  		goto out_free;
> >  
> > +	if (IS_ENABLED(CONFIG_VFIO_MDEV) && !iommu_present(bus) &&
> > +	    (bus == &mdev_bus_type)) {  
> 
> Hi Kirti,
> 
> By refering mdev_bus_type directly you are making vfio_iommu_type1.ko depends
> on mdev.ko, but in Kconfig doesn't guarantee the dependency. For example,
> if CONFIG_VFIO_IOMMU_TYPE1=y and CONFIG_VFIO_MDEV=m, the building will fail.

Good point, Jike.  I don't think we want to make existing vfio modules
dependent on mdev modules.  I wonder if we can lookup the mdev_bus_type
symbol w/o triggering the module load.  Thanks,

Alex