linux-kernel - Re: [PATCH v2 1/2] vfio/type1: Simplify bus

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Date:   Fri, 24 Jun 2022 08:11:59 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Robin Murphy <robin.murphy@....com>, cohuck@...hat.com,
        iommu@...ts.linux.dev, iommu@...ts.linux-foundation.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] vfio/type1: Simplify bus_type determination

On Thu, 23 Jun 2022 22:50:30 -0300
Jason Gunthorpe <jgg@...dia.com> wrote:

> On Thu, Jun 23, 2022 at 05:00:44PM -0600, Alex Williamson wrote:
> 
> > > >> +struct vfio_device *vfio_device_get_from_iommu(struct iommu_group *iommu_group)
> > > >> +{
> > > >> +	struct vfio_group *group = vfio_group_get_from_iommu(iommu_group);
> > > >> +	struct vfio_device *device;    
> > > > 
> > > > Check group for NULL.    
> > > 
> > > OK - FWIW in context this should only ever make sense to call with an 
> > > iommu_group which has already been derived from a vfio_group, and I did 
> > > initially consider a check with a WARN_ON(), but then decided that the 
> > > unguarded dereference would be a sufficiently strong message. No problem 
> > > with bringing that back to make it more defensive if that's what you prefer.  
> > 
> > A while down the road, that's a bit too much implicit knowledge of the
> > intent and single purpose of this function just to simply avoid a test.  
> 
> I think we should just pass the 'struct vfio_group *' into the
> attach_group op and have this API take that type in and forget the
> vfio_group_get_from_iommu().

That's essentially what I'm suggesting, the vfio_group is passed as an
opaque pointer which type1 can use for a
vfio_group_for_each_vfio_device() type call.  Thanks,

Alex