Re: [PATCH v2 06/10] PCI/LUO: Save and restore driver name

[Jason Gunthorpe <jgg@ziepe.ca>]

On Thu, Oct 02, 2025 at 02:39:26PM -0700, Chris Li wrote:
> On Tue, Sep 30, 2025 at 9:37 AM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> > As I said, I would punt all of this to the initrd and let the initrd
> > explicitly bind drivers.
> 
> You still need a mechanism to prevent after the PCI bridge scan,
> create the pci_devices, not auto probe the drivers. If it is not
> driver_override, it will be some new PCI API and liveupdate is the
> first user of it.

Yes, we need userspace to control the timing of driver binding for
Confidential Compute too, so I would prefer to see a generic proposal
that can solve both.

If this is to be a luo thing then preserving disabling driver auto
bind for specific devices could be reasonable.

> There are two slightly different things here:
> 1) modprobe the driver. That is typically control by udev.
> 2) auto probing the drive after the driver has been loaded or PCI
> device scanned.
 
> In your envisioning, the initrd autobind controls both of the above
> two spec of things, right?

Today the initrd runs udev which does the module loading and then
the kernel does driver auto binding.

You'd want to move driver binding to userspace so that userspace can
select which is the right driver for luo and for CC we want to delay
binding the drivers until after userspace has measured and verified
the device.

The idea is that userpsace, through the modules.alias file, would run
the same driver selection algorithm and signal the kernel to load the
driver.

Also, for VFIO we have addressed Greg's remarks about driver name ABI
by adding VFIO specific module.alias entries:

alias vfio_pci:v*d*sv*sd*bc*sc*i* vfio_pci
alias vfio_pci:v000015B3d0000101Esv*sd*bc*sc*i* mlx5_vfio_pci

Modern userspace is already supposed to be entering VFIO mode by using
this file and avoiding making driver name an ABI.

Jason