[vfio-users] How to choose a compatible motherboard?

[Alex Williamson]

On Thu, Oct 22, 2015 at 2:14 PM, Nick Sukharev <nicksukharev at gmail.com>
wrote:

> I had this issue with my 1st PCIE slot. Three steps helped:
> 1) disabling radeon driver by
> creating /etc/modprobe.d/blacklistradeon.conf with a single line
> blacklist radeon
> 2) specifying GRUB_CMDLINE_LINUX="nomodeset vga=normal video=vesafb:off"
> in /etc/default/grub
> 3) Using "pure" OVMF.
>

Don't you still get a VGA mode login prompt on the primary graphics on the
host?  That means the host is writing into the VGA space of the device,
even while the device is in use by the guest.  Maybe it doesn't cause any
noticeable problem since you're using OVMF, but it's still concerning.
I've tried this in the past and bumped a keyboard connected to the host
while the guest (Linux) was in text mode and got a host login prompt on the
guest-owned graphics... very confusing.  I think there's a step missing
here about detaching the VGA device from vgacon.


> I am pretty sure steps 1 and 3 are also required for secondary slots on my
> MB unless I want to use just one non-gpu slot for gpu, then it works with
> seabios.
> I still get this in dmesg:
> vfio-pci 0000:03:00.0: Invalid ROM contents
> but no issues because of that.
>

Linux has special handling for the boot VGA ROM, it's read from the shadow
ROM at 0xc0000, which isn't ROM at all and often gets modified by the ROM
execution at boot time.  Primary graphics, even if not used for a console,
is therefore always more likely to need the ROM passed as a file.


> I was trying to make all PCIE slots available for passthrough, if that is
> not required some old NVidia in the 1st slot and a radeon in the 2nd (or
> vice versa) should be easier. With 1,2,3 I can go completely "headless" in
> the sense that I am using USB graphhics on that machine for host.
> Also, Haswell i7-5820K works perfectly for x99 socket 2011-3, no need to
> go for a Xenon. I doubt you can get 6 core Xenon for a comparable price.
>

"perfectly" minus not supporting ACS on the processor root ports.  There is
still a reason to go for a Xeon.
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