Re: WARNING: CPU: 1 PID: 0 at arch/x86/kernel/cpu/cpuid-deps.c:123 do_clear_cpu_cap+0xdc/0x130 on Intel(R) Atom(TM) CPU N450 system

[Dominik 'Rathann' Mierzejewski <dominik@greysector.net>]

Hi!

On Friday, 17 October 2025 at 16:26, Dave Hansen wrote:
[...]
> That's a fun one.

I'm getting a similar trace on Fedora 42 with kernel-6.17.8:
Nov 26 23:25:43 localhost kernel: ------------[ cut here ]------------
Nov 26 23:25:43 localhost kernel: WARNING: CPU: 1 PID: 0 at arch/x86/kernel/cpu/cpuid-deps.c:123 do_clear_cpu_cap+0xdc/0x130
Nov 26 23:25:43 localhost kernel: Modules linked in:
Nov 26 23:25:43 localhost kernel: CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted 6.17.8-200.fc42.x86_64 #1 PREEMPT(lazy) 
Nov 26 23:25:43 localhost kernel: Hardware name: FOXCONN TPS01/TPS01, BIOS 080015  03/23/2010
Nov 26 23:25:43 localhost kernel: RIP: 0010:do_clear_cpu_cap+0xdc/0x130
Nov 26 23:25:43 localhost kernel: Code: 44 24 60 65 48 2b 05 5b 7f 49 03 75 67 48 83 c4 68 5b 5d 41 5c 41 5d c3 cc cc cc cc 8>
Nov 26 23:25:43 localhost kernel: RSP: 0000:ffffcb40c00bfdb0 EFLAGS: 00010002
Nov 26 23:25:43 localhost kernel: RAX: 0000000000000000 RBX: ffffcb40c00bfdb0 RCX: 0000000000000000
Nov 26 23:25:43 localhost kernel: RDX: 0000000000000001 RSI: 0000000000000070 RDI: ffffcb40c00bfe10
Nov 26 23:25:43 localhost kernel: RBP: 0000000000000070 R08: 0000000000000000 R09: ffffcb40c00bfc28
Nov 26 23:25:43 localhost kernel: R10: ffffffff90f39a88 R11: 00000000ffffdfff R12: 0000000000000000
Nov 26 23:25:43 localhost kernel: R13: 0000000000000018 R14: 0000000000000000 R15: 0000000000000000
Nov 26 23:25:43 localhost kernel: FS:  0000000000000000(0000) GS:ffff89baab6c7000(0000) knlGS:0000000000000000
Nov 26 23:25:43 localhost kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
Nov 26 23:25:43 localhost kernel: CR2: 0000000000000000 CR3: 0000000019a2c000 CR4: 00000000000006f0
Nov 26 23:25:43 localhost kernel: Call Trace:
Nov 26 23:25:43 localhost kernel:  <TASK>
Nov 26 23:25:43 localhost kernel:  early_init_intel.cold+0x47/0x112
Nov 26 23:25:43 localhost kernel:  ? cpu_parse_topology+0xa4/0x170
Nov 26 23:25:43 localhost kernel:  init_intel+0x26/0x2d0
Nov 26 23:25:43 localhost kernel:  identify_cpu+0x193/0x7d0
Nov 26 23:25:43 localhost kernel:  identify_secondary_cpu+0x4f/0xb0
Nov 26 23:25:43 localhost kernel:  ? lapic_setup_esr+0x4d/0xa0
Nov 26 23:25:43 localhost kernel:  start_secondary+0x7a/0x170
Nov 26 23:25:43 localhost kernel:  common_startup_64+0x13e/0x141
Nov 26 23:25:43 localhost kernel:  </TASK>
Nov 26 23:25:43 localhost kernel: ---[ end trace 0000000000000000 ]---
Nov 26 23:25:43 localhost kernel: ------------[ cut here ]------------

Admittedly, the machine is 15 years old.

> Could you boot the system on a known good kernel and run this, please?
> 
> 	rdmsr -a 0x000001a0
> 
> That'll dump out MSR_IA32_MISC_ENABLE on all the CPUs.

# rdmsr -a 0x000001a0
60840488
60840488
60840488
60840489

> When was the last kernel that worked for you?

Out of available Fedora kernels, the last one without the WARNING is
6.9.12.

> Also, do you have old microcode?

I have version 0x107. I think there's no newer one for Atom D510.

> Can you dump the beginning of /proc/cpuinfo, please?

# head -n 27 /proc/cpuinfo 
processor	: 0
vendor_id	: GenuineIntel
cpu family	: 6
model		: 28
model name	: Intel(R) Atom(TM) CPU D510   @ 1.66GHz
stepping	: 10
microcode	: 0x107
cpu MHz		: 1666.655
cache size	: 512 KB
physical id	: 0
siblings	: 4
core id		: 0
cpu cores	: 2
...

Regards,
Dominik
-- 
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makes sense. But the real universe is always one step beyond logic.
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