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Date:   Tue, 15 Jun 2021 21:34:17 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Alex Williamson <alex.williamson@redhat.com>
Cc:     Max Gurtovoy <mgurtovoy@nvidia.com>, cohuck@redhat.com,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        aviadye@nvidia.com, oren@nvidia.com, shahafs@nvidia.com,
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        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
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On Tue, Jun 15, 2021 at 06:22:45PM -0600, Alex Williamson wrote:
> On Tue, 15 Jun 2021 20:32:57 -0300
> Jason Gunthorpe <jgg@nvidia.com> wrote:
> 
> > On Tue, Jun 15, 2021 at 05:22:42PM -0600, Alex Williamson wrote:
> > 
> > > > > b) alone is a functional, runtime difference.    
> > > > 
> > > > I would state b) differently:
> > > > 
> > > > b) Ignore the driver-override-only match entries in the ID table.  
> > > 
> > > No, pci_match_device() returns NULL if a match is found that is marked
> > > driver-override-only and a driver_override is not specified.  That's
> > > the same as no match at all.  We don't then go on to search past that
> > > match in the table, we fail to bind the driver.  That's effectively an
> > > anti-match when there's no driver_override on the device.  
> > 
> > anti-match isn't the intention. The deployment will have match tables
> > where all entires are either flags=0 or are driver-override-only.
> 
> I'd expect pci-pf-stub to have one of each, an any-id with
> override-only flag and the one device ID currently in the table with
> no flag.

Oh Hum. Actually I think this shows the anti-match behavior is
actually a bug.. :(

For something like pci_pf_stub_whitelist, if we add a
driver_override-only using the PCI any id then it effectively disables
new_id completely because the match search will alway find the
driver_override match first and stop searching. There is no chance to
see things new_id adds.

We have to fix this patch so flags isn't an anti-match to make it work
without user regression.

Jason