linux-kernel - RE: [PATCH RFC v2 0/3] Add set_dev_data and unset_dev

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Date:   Fri, 21 Apr 2023 08:07:19 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Nicolin Chen <nicolinc@...dia.com>
CC:     "jgg@...dia.com" <jgg@...dia.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "will@...nel.org" <will@...nel.org>,
        "joro@...tes.org" <joro@...tes.org>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH RFC v2 0/3] Add set_dev_data and unset_dev_data support

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Friday, April 21, 2023 3:56 PM
> 
> On Fri, Apr 21, 2023 at 07:47:13AM +0000, Tian, Kevin wrote:
> 
> > > It is in the commit message of the cover-letter though:
> > >
> https://github.com/nicolinc/iommufd/commit/5e17d270bfca2a5e3e7401d4b
> > > f58ae53eb7a8a55
> > > --------------------------------------------------------
> > > Changelog
> > > v2:
> > >  * Integrated the uAPI into VFIO_DEVICE_BIND_IOMMUFD call
> > >  * Renamed the previous set_rid_user to set_dev_data, to decouple from
> > >    the PCI regime.
> > > v1:
> > >  https://lore.kernel.org/all/cover.1680762112.git.nicolinc@nvidia.com/
> > > --------------------------------------------------------
> > >
> > > > Could you add some words why changing from passing the information
> > > > in an iommufd ioctl to bind_iommufd? My gut-feeling leans toward
> > > > the latter option...
> > >
> > > Yea. Jason told me to decouple it from PCI. And merge it into
> > > a general uAPI. So I picked the BIND ioctl.
> > >
> >
> > 'decouple it from PCI' is kind of covered by renaming set_rid
> > to set_data. but I didn't get why this has to be merged with another
> > uAPI. Once iommufd_device is created we could have separate
> > ioctls to poke its attributes individually. What'd be broken if this
> > is not done at BIND time?
> 
> Oh, sorry. He didn't literally told me to merge, but commented
> "make sense" at my proposal of reusing BIND. So, I don't think
> adding to the BIND is a must here.
> 
> The BIND is done in vfio_realize() where the RID (dev_data) is
> available also. And the new uAPI in my v1 actually gets called
> near the BIND. So, I feel we may just do it once? I am open to
> a better idea.
> 

IMHO if this can be done within iommufd then that should be
the choice. vfio doesn't need to know this data at all and doing
so means vdpa or a 3rd driver also needs to implement similar 
logic in their uAPI...