[RFC][PATCH] x86/smp: Fix __max_logical_packages value setup

Jiri Olsa
2016-08-03T16:24:26Z

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 <framsay@redhat.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
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