linux-kernel - Re: [PATCH RFC] x86/cpu: fix intermittent lockup on poweroff

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Date:   Wed, 26 Apr 2023 15:02:10 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Tony Battersby <tonyb@...ernetics.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Mario Limonciello <mario.limonciello@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] x86/cpu: fix intermittent lockup on poweroff

> > > This is probably going to pull in a cache line and cause the problem the
> > > native_wbinvd() is trying to avoid.
> > 
> > Is one _more_ cacheline really the problem?
> 
> The answer is it depends. If the cacheline ends up modified/dirty, then it
> can be a problem.

I haven't followed this all in detail, but if any dirty cache line a
problem you probably would need to be sure that any possible NMI user
(like perf or watchdogs) is disabled at this point, otherwise you could
still get NMIs here. 

I don't think perf currently has a mechanism to do that other
than to offline the CPU.

Also there are of course machine checks and SMIs that could still happen, 
but I guess there's nothing you could do about them.

-Andi