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Date:   Tue, 8 Jun 2021 19:27:11 -0600
From:   Alex Williamson <alex.williamson@redhat.com>
To:     Jason Gunthorpe <jgg@nvidia.com>
Cc:     Max Gurtovoy <mgurtovoy@nvidia.com>, cohuck@redhat.com,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
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        parav@nvidia.com, artemp@nvidia.com, kwankhede@nvidia.com,
        ACurrid@nvidia.com, cjia@nvidia.com, yishaih@nvidia.com,
        kevin.tian@intel.com, hch@infradead.org, targupta@nvidia.com,
        shameerali.kolothum.thodi@huawei.com, liulongfang@huawei.com,
        yan.y.zhao@intel.com
Subject: Re: [PATCH 09/11] PCI: add matching checks for driver_override
 binding
Message-ID: <20210608192711.4956cda2.alex.williamson@redhat.com>
In-Reply-To: <20210608224517.GQ1002214@nvidia.com>
References: <20210603160809.15845-1-mgurtovoy@nvidia.com>
        <20210603160809.15845-10-mgurtovoy@nvidia.com>
        <20210608152643.2d3400c1.alex.williamson@redhat.com>
        <20210608224517.GQ1002214@nvidia.com>
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On Tue, 8 Jun 2021 19:45:17 -0300
Jason Gunthorpe <jgg@nvidia.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