Frank reported kernel panic when he disabled several cores in BIOS via following option:
Core Disable Bitmap(Hex) [0] with number 0xFFE, which leaves 16 CPUs in system (out of 48). The kernel panic below goes along with following messages: smpboot: Max logical packages: 2^M smpboot: APIC(0) Converting physical 0 to logical package 0^M smpboot: APIC(20) Converting physical 1 to logical package 1^M smpboot: APIC(40) Package 2 exceeds logical package map^M smpboot: CPU 8 APICId 40 disabled^M smpboot: APIC(60) Package 3 exceeds logical package map^M smpboot: CPU 12 APICId 60 disabled^M ... general protection fault: 0000 [#1] SMP^M Modules linked in:^M CPU: 15 PID: 1 Comm: swapper/0 Not tainted 4.7.0-rc5+ #1^M Hardware name: SGI UV300/UV300, BIOS SGI UV 300 series BIOS 05/25/2016^M task: ffff8801673e0000 ti: ffff8801673ac000 task.ti: ffff8801673ac000^M RIP: 0010:[<ffffffff81014d54>] [<ffffffff81014d54>] uncore_change_context+0xd4/0x180^M ... [<ffffffff810158ac>] uncore_event_init_cpu+0x6c/0x70^M [<ffffffff81d8c91c>] intel_uncore_init+0x1c2/0x2dd^M [<ffffffff81d8c75a>] ? uncore_cpu_setup+0x17/0x17^M [<ffffffff81002190>] do_one_initcall+0x50/0x190^M [<ffffffff810ab193>] ? parse_args+0x293/0x480^M [<ffffffff81d87365>] kernel_init_freeable+0x1a5/0x249^M [<ffffffff81d86a35>] ? set_debug_rodata+0x12/0x12^M [<ffffffff816dc19e>] kernel_init+0xe/0x110^M [<ffffffff816e93bf>] ret_from_fork+0x1f/0x40^M [<ffffffff816dc190>] ? rest_init+0x80/0x80^M The reason for the panic is wrong value of __max_logical_packages, which lets logical_package_map uninitialized and the uncore code relying on this map being properly initialized (maybe we should add some safety checks there as well). The __max_logical_packages is computed as: DIV_ROUND_UP(total_cpus, ncpus); - ncpus being number of cores With above BIOS setup we get total_cpus == 16 which set __max_logical_packages to 2 (ncpus is 12). Once topology_update_package_map processes CPU with logical pkg over 2 we display above messages and fail to initialize the physical_to_logical_pkg map, which makes the uncore code crash. The fix is to set __max_logical_packages directly to total_cpus, which should be the maximum possible logical ID of the pkg in any case. Reported-by: Frank Ramsay <[email protected]> Signed-off-by: Jiri Olsa <[email protected]> --- diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 157bf0957219..484f7d357c77 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -340,7 +340,7 @@ static void __init smp_init_package_map(void) ncpus = 1; } - __max_logical_packages = DIV_ROUND_UP(total_cpus, ncpus); + __max_logical_packages = total_cpus; /* * Possibly larger than what we need as the number of apic ids per
