linux-kernel - Re: [PATCH 09/11] PCI: add matching checks for driver

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Date:   Tue, 8 Jun 2021 19:27:11 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Max Gurtovoy <mgurtovoy@...dia.com>, cohuck@...hat.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        aviadye@...dia.com, oren@...dia.com, shahafs@...dia.com,
        parav@...dia.com, artemp@...dia.com, kwankhede@...dia.com,
        ACurrid@...dia.com, cjia@...dia.com, yishaih@...dia.com,
        kevin.tian@...el.com, hch@...radead.org, targupta@...dia.com,
        shameerali.kolothum.thodi@...wei.com, liulongfang@...wei.com,
        yan.y.zhao@...el.com
Subject: Re: [PATCH 09/11] PCI: add matching checks for driver_override
 binding

On Tue, 8 Jun 2021 19:45:17 -0300
Jason Gunthorpe <jgg@...dia.com> wrote:

> On Tue, Jun 08, 2021 at 03:26:43PM -0600, Alex Williamson wrote:
> > > drivers that specifically opt into this feature and the driver now has
> > > the opportunity to provide a proper match table that indicates what HW
> > > it can properly support. vfio-pci continues to support everything.  
> > 
> > In doing so, this also breaks the new_id method for vfio-pci.    
> 
> Does it? How? The driver_override flag is per match entry not for the
> entire device so new_id added things will work the same as before as
> their new match entry's flags will be zero.

Hmm, that might have been a testing issue; combining driverctl with
manual new_id testing might have left a driver_override in place.
 
> > Sorry, with so many userspace regressions, crippling the
> > driver_override interface with an assumption of such a narrow focus,
> > creating a vfio specific match flag, I don't see where this can go.
> > Thanks,  
> 
> On the other hand it overcomes all the objections from the last go
> round: how userspace figures out which driver to use with
> driver_override and integrating the universal driver into the scheme.
> 
> pci_stub could be delt with by marking it for driver_override like
> vfio_pci.

By marking it a "vfio driver override"? :-\

> But driverctl as a general tool working with any module is not really
> addressable.
> 
> Is the only issue the blocking of the arbitary binding? That is not a
> critical peice of this, IIRC

We can't break userspace, which means new_id and driver_override need
to work as they do now.  There are scads of driver binding scripts in
the wild, for vfio-pci and other drivers.  We can't assume such a
narrow scope.  Thanks,

Alex