Am Mittwoch, 11. September 2024, 10:53:30 schrieb Niels Dettenbach:
> 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 assuming a "crash kernel" and disable
> SMT (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 SMT / all CPUs as in the past to such DomU
> VMs.
>
> Signed-off-by: Niels Dettenbach <nd@xxxxxxxxxxxx>
>
Signed-off-by: Niels Dettenbach <nd@xxxxxxxxxxxx>
---
A reworked proposal patch which substitutes my initial proposed patch:
--- linux/arch/x86/kernel/cpu/topology.c 2024-09-11 17:42:42.699278317 +0200
+++ linux/arch/x86/kernel/cpu/topology.c.orig 2024-09-11 09:53:16.194095250 +0200
@@ -132,14 +132,6 @@
u64 msr;
/*
- * assume Xen PV has a working (special) topology
- */
- if (xen_pv_domain()) {
- topo_info.real_bsp_apic_id = topo_info.boot_cpu_apic_id;
- return false;
- }
-
- /*
* There is no real good way to detect whether this a kdump()
* kernel, but except on the Voyager SMP monstrosity which is not
* longer supported, the real BSP APIC ID is the first one which is
