linux-kernel - Re: [patch 02/10] x86/mce: Disable tracing and kprobes on do_machine

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Message-ID: <20200226185945.GC18400@hirez.programming.kicks-ass.net>
Date:   Wed, 26 Feb 2020 19:59:45 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Andy Lutomirski <luto@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Brian Gerst <brgerst@...il.com>,
        Juergen Gross <JGross@...e.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [patch 02/10] x86/mce: Disable tracing and kprobes on
 do_machine_check()

On Wed, Feb 26, 2020 at 07:42:37PM +0100, Borislav Petkov wrote:
> On Wed, Feb 26, 2020 at 09:28:51AM -0800, Andy Lutomirski wrote:
> > > It entirely depends on what the goal is :-/ On the one hand I see why
> > > people might want function tracing / kprobes enabled, OTOH it's all
> > > mighty frigging scary. Any tracing/probing/whatever on an MCE has the
> > > potential to make a bad situation worse -- not unlike the same on #DF.
> 
> FWIW, I had this at the beginning of the #MC handler in a feeble attempt
> to poke at this:
> 
> +       hw_breakpoint_disable();
> +       static_key_disable(&__tracepoint_read_msr.key);
> +       tracing_off();

You can't do static_key_disable() from an IST