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

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Message-ID: <BN9PR11MB5276A79834CCB5954A3025DF8CB59@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Thu, 23 Jun 2022 08:46:45 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        Robin Murphy <robin.murphy@....com>
CC:     "cohuck@...hat.com" <cohuck@...hat.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 1/2] vfio/type1: Simplify bus_type determination

> From: Alex Williamson <alex.williamson@...hat.com>
> Sent: Thursday, June 23, 2022 6:17 AM
> 
> >
> >  	ret = -EIO;
> > -	domain->domain = iommu_domain_alloc(bus);
> > +	domain->domain = iommu_domain_alloc(iommu_api_dev->dev-
> >bus);
> 
> It makes sense to move away from a bus centric interface to iommu ops
> and I can see that having a device interface when we have device level
> address-ability within a group makes sense, but does it make sense to
> only have that device level interface?  For example, if an iommu_group
> is going to remain an aspect of the iommu subsystem, shouldn't we be
> able to allocate a domain and test capabilities based on the group and
> the iommu driver should have enough embedded information reachable
> from
> the struct iommu_group to do those things?  This "perform group level
> operations based on an arbitrary device in the group" is pretty klunky.
> Thanks,
> 

This sounds a right thing to do.

btw another alternative which I'm thinking of is whether vfio_group
can record the bus info when the first device is added to it in
__vfio_register_dev(). Then we don't need a group interface from
iommu to test if vfio is the only user having such requirement.