linux-kernel - Re: Kernel 6.9 regression: X86: Bogus messages from topology detection

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Date: Mon, 27 May 2024 15:14:26 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Peter Schneider <pschneider1968@...glemail.com>
Cc: LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
 stable@...r.kernel.org, regressions@...ts.linux.dev
Subject: Re: Kernel 6.9 regression: X86: Bogus messages from topology detection

On Mon, May 27 2024 at 09:29, Peter Schneider wrote:
> This is coming from an older server machine: 2-socket Ivy Bridge Xeon E5-2697 v2 (24C/48T) 
> in an Asus Z9PE-D16/2L motherboard (Intel C-602A chipset); BIOS patched to the latest 
> available from Asus. All memory slots occupied, so 256 GB RAM in total.
>
>  From a "good boot", e.g. kernel 6.8.11, dmesg output looks like this:
>
> [    1.823797] smpboot: x86: Booting SMP configuration:
> [    1.823799] .... node  #0, CPUs:        #1  #2  #3  #4  #5  #6  #7  #8  #9 #10 #11
> [    1.827514] .... node  #1, CPUs:   #12 #13 #14 #15 #16 #17 #18 #19 #20 #21 #22 #23
> [    0.011462] smpboot: CPU 12 Converting physical 0 to logical die 1
>
> [    1.875532] .... node  #0, CPUs:   #24 #25 #26 #27 #28 #29 #30 #31 #32 #33 #34 #35
> [    1.882453] .... node  #1, CPUs:   #36 #37 #38 #39 #40 #41 #42 #43 #44 #45 #46 #47
> [    1.887532] MDS CPU bug present and SMT on, data leak possible. See 
> https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/mds.html for more details.
> [    1.933640] smp: Brought up 2 nodes, 48 CPUs
> [    1.933640] smpboot: Max logical packages: 2
> [    1.933640] smpboot: Total of 48 processors activated (259199.61 BogoMIPS)
>
>
>  From a "bad" boot, e.g. kernel 6.9.2, dmesg output has these messages in it:
>
> [    1.785937] smpboot: x86: Booting SMP configuration:
> [    1.785939] .... node  #0, CPUs:        #4
> [    1.786215] .... node  #1, CPUs:   #12 #16

Yuck. That does not make any sense.

> [    1.797547] .... node  #0, CPUs:    #1  #2  #3  #5  #6  #7  #8  #9 #10 #11
> [    1.801858] .... node  #1, CPUs:   #13 #14 #15 #17 #18 #19 #20 #21 #22 #23
> [    1.804687] .... node  #0, CPUs:   #24 #25 #26 #27 #28 #29 #30 #31 #32 #33 #34 #35
> [    1.810728] .... node  #1, CPUs:   #36 #37 #38 #39 #40 #41 #42 #43 #44 #45 #46 #47

> However the machine boots, and except from these strange messages, I cannot detect any 
> other abnormal behaviour. It is running ~15 QEMU/KVM virtual machines just fine. Because 
> these messages look unusual and a bit scary though, I have bisected the issue, to be able 
> to report it here. The first bad commit I found is this one:

Ok. So as the machine is booting, can you please provide the output of:

 cat /sys/kernel/debug/x86/topo/cpus/*

on the 6.9 kernel and 

 cat /proc/cpuinfo

for both 6.8 and 6.9?

Thanks,

        tglx