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Re: [Xen-devel] [Qemu-devel] [v2][PATCH 4/8] xen, gfx passthrough: reserve 00:02.0 for INTEL IGD


> I think '-vga none' just guarantees the qemu vga cards doesn't occupy
> 00:02.0, but this doesn't mean others use this specific slot since in
> qemu internal, we always pass -1 to assign a slot automatically to
> register a PCI device. So in some cases, we can't get this slot as we
> expect since that is already assigned previously before we need this.

Yes, -vga, -net nic, -drive if=scsi (maybe more) can internally create
pci devices with auto slot assignment, which will occupy slot 2 indeed.
Use -device instead to create the devices.

> PCI: slot 2 function 0 not available for xen-pci-passthrough, in use by 
> xen-platform

Ah, the xen platform device.  /me looks.  Ah, pc_xen_hvm_init creates
this automatically.  Two options here IMHO:

  (1) Just move it somewhere else explicitly.  For example slot 3, or
      make it a southbridge function (say 00:01.7).
  (2) Don't create it automatically, instead expect management add it
      if needed, using -device xen-plaform,addr=...

I personally would suggest to go for #2.  As far I know the platform
device is only needed if you want attach xenbus devices to the guest
(correct?), so creating virtual machines without the xen platform device
is a valid use case and you should allow it.


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