linux-kernel - Re: [tip:x86/alternatives] [x86/alternatives] ee8962082a: WARNING:at_arch/x86/kernel/cpu/cpuid-deps.c:#do_clear_cpu

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Date: Mon, 6 May 2024 15:09:27 +0800
From: Oliver Sang <oliver.sang@...el.com>
To: Borislav Petkov <bp@...en8.de>
CC: Sean Christopherson <seanjc@...gle.com>, <oe-lkp@...ts.linux.dev>,
	<lkp@...el.com>, <linux-kernel@...r.kernel.org>, <x86@...nel.org>, "Ingo
 Molnar" <mingo@...nel.org>, Srikanth Aithal <sraithal@....com>,
	<oliver.sang@...el.com>
Subject: Re: [tip:x86/alternatives] [x86/alternatives] ee8962082a:
 WARNING:at_arch/x86/kernel/cpu/cpuid-deps.c:#do_clear_cpu_cap

hi, Boris,

On Sat, May 04, 2024 at 02:48:22PM +0200, Borislav Petkov wrote:
> On Wed, May 01, 2024 at 12:33:05AM +0200, Borislav Petkov wrote:
> > On Tue, Apr 30, 2024 at 12:51:02PM -0700, Sean Christopherson wrote:
> > > But that would just mask the underlying problem, it wouldn't actually fix anything
> > > other than making the WARN go away.  Unless I'm misreading the splat+code, the
> > > issue isn't that init_ia32_feat_ctl() clears VMX late, it's that the BSP sees
> > > VMX as fully enabled, but at least one AP sees VMX as disabled.
> > > 
> > > I don't see how the kernel can expect to function correctly with divergent feature
> > > support across CPUs, i.e. the WARN is a _good_ thing in this case, because it
> > > alerts the user that their system is messed up, e.g. has a bad BIOS or something.
> > 
> > Yes, and yes.
> > 
> > There are two issues. Clearing feature flags after alternatives have
> > been applied should not happen, and this particular issue with that box.
> > 
> > Lemme cook up something in the coming days for the former.
> 
> Two simple patches as a reply to this.
> 
> Oliver, can you run them on your box pls?

we confirmed after applying them upon ee8962082a, the WARNING which was reported
in our original report cannot be reproduced any longer.

Tested-by: kernel test robot <oliver.sang@...el.com>

> 
> Thx.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette