Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 26 Apr 2023 15:02:10 -0700
From:   Andi Kleen <ak@linux.intel.com>
To:     Tom Lendacky <thomas.lendacky@amd.com>
Cc:     Dave Hansen <dave.hansen@intel.com>,
        Tony Battersby <tonyb@cybernetics.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Mario Limonciello <mario.limonciello@amd.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RFC] x86/cpu: fix intermittent lockup on poweroff
Message-ID: <ZEmfYpOyyul4BaKP@tassilo>
References: <3817d810-e0f1-8ef8-0bbd-663b919ca49b@cybernetics.com>
 <f5c7a104-d422-bd02-d361-e9e9f433d41d@intel.com>
 <87o7nbzn8w.ffs@tglx>
 <5f8a9cb8-70cf-2a17-cfc4-cb31cb658de4@cybernetics.com>
 <87y1mey503.ffs@tglx>
 <ccf57fd2-45b8-1f1f-f46a-55d7f4c56161@cybernetics.com>
 <01a44722-931a-7aff-4f4b-75e78855beb1@amd.com>
 <25dd25d3-2db1-acf6-0814-9bb5bcd65bb9@intel.com>
 <469754ab-d8ec-168a-15c7-61045a880792@amd.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <469754ab-d8ec-168a-15c7-61045a880792@amd.com>
Precedence: bulk

> > > 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