[vfio-users] vfio-pci late loading, built-in or initramfs

[Alex Williamson]

On Tue, 11 Oct 2016 22:09:06 -0700
Muted Bytes <mutedbytes at gmail.com> wrote:

> I have recently installed an AMD card for my host system, and my vm
> guest is also using an AMD card. On the host, I am using radeon driver
> but would like to prevent the guest getting radeon loaded. With
> pci-stub, with it built-in to the kernel, it would always grab pci
> devices before any other driver got the chance. However, with vfio-pci
> it seems to be loaded much later in the boot process, so radeon gets
> both cards before vfio-pci can bind it. As a result, I have tried
> building vfio and vfio-pci as modules and then including them in a
> Dracut-created initramfs as detailed at
> https://vfio.blogspot.com/2015/05/vfio-gpu-how-to-series-part-3-host.html.
> Even doing this, vfio-pci still gets loaded as late as it was built-in
> to the kernel, and so it does not get loaded before radeon (which is
> built-in).
> 
> Is there a way to get vfio-pci loaded earlier? Do I need to just build
> radeon as module to hope it gets loaded later also?

If radeon is built-in, you're causing your own problems.  There is no
way to get a module to load prior to a built-in driver.  Even ordering
of built-in drivers is based on link ordering.  This is part of why we
use modules.  Modules are a good thing.  I'd guess your only hope is to
have pci-stub built-in and hope the link order lets it probe the
devices first, then sort out later how to get the correct devices bound
to vfio-pci vs radeon.  Thanks,

Alex