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@syndicat.com
Signed-off-by: Niels Dettenbach nd@syndicat.com ---
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