Xen on Zen 3

[Matyáš Kroupa <kroupa.matyas@xxxxxxxxx>]

Hi,
I am trying to run Xen on a bare metal with Zen 3 microarchitecture (to be 
specific Ryzen 9 5950X). I am using Fedora 43 as Dom0 in PVH mode. However, the 
Linux kernel crashes early in the boot causing Xen to reboot. I am not exactly 
sure if Linux or Xen is the problematic part. The kernel boots fine without 
Xen. Before Ryzen 9 I had Ryzen 5 3400G (Zen+) which booted even with Xen.

The Xen is a backported from Fedora 44 (not yet released) because I need Xen 
4.21 features, mainly ReBAR support for the Arc B50 GPU. Package specification 
with build commands can be found on https://src.fedoraproject.org/rpms/xen/
blob/f44/f/xen.spec. There are also downstream patches and configuration.

I have set up a serial link, so I have some logs. They are in the attachment. 
I have used gdb to translate the binary offset to source code line. The 
problematic line is https://elixir.bootlin.com/linux/v6.19.10/source/arch/x86/
kernel/amd_node.c#L296. It seems that linux is detecting zero PCI roots on 
non-zero number of nodes causing division by zero.

System information
Boot mode: UEFI
Secure boot: disabled
IOMMU: enabled
SR-IOV: enabled
Above 4G decoding & rebar: enabled
Xen cmdline: placeholder dom0=pvh dom0_mem=36G com1=115200,8n1 
console=com1,vga no-real-mode edd=off
Linux cmdline: placeholder root=UUID=5a7af636-54c3-4f76-a164-c1138de257ad ro 
rootflags=subvol=@ rhgb quiet console=hvc0 earlyprintk=xen
Xen version: 4.21.1
Linux version: 6.19.10

If you need more logs or other information, I will be more than happy to 
provide it.
Thank you in advance
Matyáš Kroupa

Attachment: xen-4.21.1-linux-6.19.10.log
Description: Text Data