From 5e25eb25dae9fa0700bbe42aff0e2f105fcd096a Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 22 Mar 2024 19:56:38 +0100 Subject: x86/topology: Handle the !APIC case gracefully If there is no local APIC enumerated and registered then the topology bitmaps are empty. Therefore, topology_init_possible_cpus() will die with a division by zero exception. Prevent this by registering a fake APIC id to populate the topology bitmap. This also allows to use all topology query interfaces unconditionally. It does not affect the actual APIC code because either the local APIC address was not registered or no local APIC could be detected. Fixes: f1f758a80516 ("x86/topology: Add a mechanism to track topology via APIC IDs") Reported-by: Guenter Roeck Reported-by: Linus Torvalds Signed-off-by: Thomas Gleixner Signed-off-by: Borislav Petkov (AMD) Tested-by: Guenter Roeck Link: https://lore.kernel.org/r/20240322185305.242709302@linutronix.de --- arch/x86/kernel/cpu/topology.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c index 3259b1d4fefe3c..aaca8d235dc2bb 100644 --- a/arch/x86/kernel/cpu/topology.c +++ b/arch/x86/kernel/cpu/topology.c @@ -415,6 +415,17 @@ void __init topology_init_possible_cpus(void) unsigned int total = assigned + disabled; u32 apicid, firstid; + /* + * If there was no APIC registered, then fake one so that the + * topology bitmap is populated. That ensures that the code below + * is valid and the various query interfaces can be used + * unconditionally. This does not affect the actual APIC code in + * any way because either the local APIC address has not been + * registered or the local APIC was disabled on the command line. + */ + if (topo_info.boot_cpu_apic_id == BAD_APICID) + topology_register_boot_apic(0); + if (!restrict_to_up()) { if (WARN_ON_ONCE(assigned > nr_cpu_ids)) { disabled += assigned - nr_cpu_ids; -- cgit 1.2.3-korg