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Message-ID: <7080ee37ce53d5559ba85f72a0ff59b4bc5a083d.camel@kernel.crashing.org>
Subject: Re: WARNING in lmce_supported() during reboot.
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Dave Hansen <dave.hansen@intel.com>,
        Kuniyuki Iwashima
 <kuniyu@amazon.com>, x86@kernel.org,
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Cc: Tony Luck <tony.luck@intel.com>, Borislav Petkov <bp@alien8.de>,
        Thomas
 Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        Dave Hansen
	 <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Alex Graf
	 <graf@amazon.de>
Date: Sat, 26 Oct 2024 13:33:30 +1100
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On Fri, 2024-10-25 at 16:58 -0700, Dave Hansen wrote:
>=20
> Hi Folks,
>=20
> We really do need it to be reproduced on mainline.=C2=A0 At the very leas=
t,
> it would be greatly appreciated if you could summarize what your fork is
> doing and why you don't think it is responsible.
>=20
> But I don't see how this could be timing related.=C2=A0 That MSR gets loc=
ked
> early from what I can tell, long before the system would be rebooting.
>=20
> 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.=C2=A0 If those values differ, when it got changed.
>=20
> 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.