On Thu, Sep 12, 2024 at 10:48:14AM +0200, Niels Dettenbach wrote:
> Virtual machines under Xen Hypervisor (DomU) running in Xen PV mode use a
> special, nonstandard synthetized CPU topology which "just works" under
> kernels 6.9.x while newer kernels wrongly assuming a "crash kernel" and
> disable SMP (reducing to one CPU core) because the newer topology
> implementation produces a wrong error "[Firmware Bug]: APIC enumeration
> order not specification compliant" after new topology checks which are
> improper for Xen PV platform. As a result, the kernel disables SMT and
> activates just one CPU core within the VM (DomU).
>
> The patch disables the regarding checks if it is running in Xen PV
> mode (only) and bring back SMP / all CPUs as in the past to such DomU
> VMs.
>
> Signed-off-by: Niels Dettenbach <nd@xxxxxxxxxxxx>
>
> ---
>
>
> The current behaviour leads all of our production Xen Host platforms
> (amd64 - HPE proliant) unusable after updating to newer linux kernels
> (with just one CPU available/activated per VM) while older kernels and
> other OS (current NetBSD PV DomU) still work fully (and stable since many
> years on the platform).
>
> Xen PV mode is still provided by current Xen and widely used - even
> if less wide as the newer Xen PVH mode today. So a solution probably
> will be required.
>
> So we assume that bug affects stable@xxxxxxxxxxxxxxx as well.
>
<formletter>
This is not the correct way to submit patches for inclusion in the
stable kernel tree. Please read:
https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.
</formletter>
