linux-kernel - Re: WARNING in lmce_supported() during reboot.

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Message-ID: <7080ee37ce53d5559ba85f72a0ff59b4bc5a083d.camel@kernel.crashing.org>
Date: Sat, 26 Oct 2024 13:33:30 +1100
From: Benjamin Herrenschmidt <benh@...nel.crashing.org>
To: Dave Hansen <dave.hansen@...el.com>,
        Kuniyuki Iwashima
 <kuniyu@...zon.com>, x86@...nel.org,
        linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Tony Luck <tony.luck@...el.com>, Borislav Petkov <bp@...en8.de>,
        Thomas
 Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Dave Hansen
	 <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Alex Graf
	 <graf@...zon.de>
Subject: Re: WARNING in lmce_supported() during reboot.

On Fri, 2024-10-25 at 16:58 -0700, Dave Hansen wrote:
> 
> Hi Folks,
> 
> We really do need it to be reproduced on mainline.  At the very least,
> it would be greatly appreciated if you could summarize what your fork is
> doing and why you don't think it is responsible.
> 
> But I don't see how this could be timing related.  That MSR gets locked
> early from what I can tell, long before the system would be rebooting.
> 
> Your best bet is going to be getting a handle on what
> MSR_IA32_FEAT_CTL's value was after the CPU was brought up and when this
> reboot was attempted.  If those values differ, when it got changed.
> 
> I'd _suspect_ some kind of BIOS sleep/wakeup wonkiness where something
> forgot to re-lock the MSR.

So far we just happened to notice it in the serial console while doing
other things, I told Kuniyuki to forward it to you in case it rings a
bell. We can definitely do some more systematic attempts at reproducing
but that might take a while.

For me it happened once while rebooting a c5d.4xlarge instance, and not
since (I tried a few reboots), so it could well be something BIOS related
(CC'ing Alex).

This is a KVM/Nitro guest, so the CPU is somewhat virtualized, but
/proc/cpuinfo says: Intel(R) Xeon(R) Platinum 8124M CPU @ 3.00GHz

Cheers,
Ben.