linux-kernel - Re: [patch V4 part 4 11/24] x86/mce: Use untraced rd/wrmsr in the MCE offline/crash check

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Date:   Thu, 14 May 2020 22:24:45 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [patch V4 part 4 11/24] x86/mce: Use untraced rd/wrmsr in the MCE
 offline/crash check

On Tue, May 5, 2020 at 7:16 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> mce_check_crashing_cpu() is called right at the entry of the MCE
> handler. It uses mce_rdmsr() and mce_wrmsr() which are wrappers around
> rdmsr() and wrmsr() to handle the MCE error injection mechanism, which is
> pointless in this context, i.e. when the MCE hits an offline CPU or the
> system is already marked crashing.
>
> The MSR access can also be traced, so use the untraceable variants. This
> is also safe vs. XEN paravirt as these MSRs are not affected by XEN PV
> modifications.


Acked-by: Andy Lutomirski <luto@...nel.org>