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

[Dave Hansen <dave.hansen@intel.com>]

On 10/17/25 07:05, Salvatore Bonaccorso wrote:
> [    0.008282] RAX: 0000000000000000 RBX: ffffcd5fc00bfd18 RCX: 0000000000000000
> [    0.008282] RDX: 0000000000000001 RSI: 0000000000000070 RDI: ffffcd5fc00bfd78
> [    0.008282] RBP: 0000000000000070 R08: 0000000000000000 R09: 706f20676e697274
> [    0.008282] R10: 7473207473616620 R11: 64656c6261736944 R12: ffffffffb8f20ba0
> [    0.008282] R13: ffff8ad332718090 R14: 000000000000061c R15: 0000000000000000
> [    0.008282] FS:  0000000000000000(0000) GS:ffff8ad378ec7000(0000) knlGS:0000000000000000
> [    0.008282] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    0.008282] CR2: 0000000000000000 CR3: 000000005842c000 CR4: 00000000000006f0
> [    0.008282] Call Trace:
> [    0.008282]  <TASK>
> [    0.008282]  do_clear_cpu_cap+0x106/0x130
> [    0.008282]  early_init_intel.cold+0x4d/0x11a
> [    0.008282]  init_intel+0x2a/0x2c0
> [    0.008282]  identify_cpu+0x18c/0x750
> [    0.008282]  identify_secondary_cpu+0x50/0xa0
> [    0.008282]  start_secondary+0x7c/0x160
> [    0.008282]  common_startup_64+0x13e/0x141
> [    0.008282]  </TASK>
> [    0.008282] ---[ end trace 0000000000000000 ]---
> [    0.354753] smp: Brought up 1 node, 2 CPUs
> [    0.354797] smpboot: Total of 2 processors activated (6666.06 BogoMIPS)
> 
> Any ideas?

That's a fun one.

This looks to be this code:

                        pr_info("Disabled fast string operations\n");
                        setup_clear_cpu_cap(X86_FEATURE_REP_GOOD);
 
because we can see the pr_info() and I'm assuming that the 'feature' is
X86_FEATURE_REP_GOOD (0x70) which we can see in RSI/RBP.

But X86_FEATURE_REP_GOOD isn't even a real CPU feature, it's one of the
synthetic ones. The only way I can see this happening is if
MSR_IA32_MISC_ENABLE_FAST_STRING is mismatched between the boot CPU and
a secondary.

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.

When was the last kernel that worked for you? Also, do you have old
microcode? Can you dump the beginning of /proc/cpuinfo, please?

processor	: 21
vendor_id	: GenuineIntel
cpu family	: 6
model		: 170
model name	: Intel(R) Core(TM) Ultra 7 155H
stepping	: 4
microcode	: 0x24

I can see your microcode version in dmesg, but not the cpu
model/family/stepping.