linux-kernel - Re: [PATCH] perf/x86/amd: Change NMI latency mitigation to use a timestamp

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Message-ID: <alpine.DEB.2.21.1908012352390.1789@nanos.tec.linutronix.de>
Date:   Thu, 1 Aug 2019 23:59:45 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Jerry Hoemann <jerry.hoemann@....com>
Subject: Re: [PATCH] perf/x86/amd: Change NMI latency mitigation to use a
 timestamp

On Thu, 1 Aug 2019, Peter Zijlstra wrote:
> On Thu, Aug 01, 2019 at 11:34:23PM +0200, Thomas Gleixner wrote:
> > Avoid the whole NMI mess, make the PMC interrupt a proper vector in the
> > highest prio bucket and instead of using CLI/STI use CR8. That would have
> > the additional advantage that we could prevent perf "NMI" then occsionally :)
> 
> Exactly, and not only the PMC, we can basically start giving out actual
> vectors on register_nmi_handler() and do away with all that shared line
> crap.
> 
> And then the actual NMI line will be mostly empty again, and it can read
> its stupid slow reason port again.
> 
> One complication though; IRET et al only do EFLAGS, not CR8, so that's
> going to be massive fun :-(
> 
> Did I say I hates the x86 interrupt scheme?

You're not alone.

That stuff definitely violates article 3 of the Convention for the
Protection of Human Rights and Fundamental Freedoms.