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

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Date:   Wed, 26 Feb 2020 11:09:03 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Borislav Petkov <bp@...en8.de>, 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 Feb 26, 2020, at 10:59 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> 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

Can we set a percpu variable saying “in some stupid context, don’t trace”?