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From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Schneider <pschneider1968@googlemail.com>
Cc: LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
 stable@vger.kernel.org, regressions@lists.linux.dev
Subject: Re: Kernel 6.9 regression: X86: Bogus messages from topology detection
In-Reply-To: <877cffcs7h.ffs@tglx>
References: <877cffcs7h.ffs@tglx>
Date: Mon, 27 May 2024 22:49:35 +0200
Message-ID: <87jzjfaskg.ffs@tglx>
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On Mon, May 27 2024 at 15:14, Thomas Gleixner wrote:
> 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?

And once the output of:

  cpuid -r

no matter on which kernel please?

Thanks,

        tglx