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Date:   Wed, 26 Feb 2020 14:28:50 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Andy Lutomirski <luto@kernel.org>
Cc:     Frederic Weisbecker <frederic@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Steven Rostedt <rostedt@goodmis.org>,
        Brian Gerst <brgerst@gmail.com>,
        Juergen Gross <jgross@suse.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Arnd Bergmann <arnd@arndb.de>
Subject: Re: [patch 02/10] x86/mce: Disable tracing and kprobes on
 do_machine_check()
Message-ID: <20200226132850.GX18400@hirez.programming.kicks-ass.net>
References: <20200225213636.689276920@linutronix.de>
 <20200225220216.315548935@linutronix.de>
 <20200226011349.GH9599@lenoir>
 <d9bde3a6-1e19-1340-1fda-bc6de2eb4f7c@kernel.org>
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On Tue, Feb 25, 2020 at 09:29:00PM -0800, Andy Lutomirski wrote:

> >> +void notrace do_machine_check(struct pt_regs *regs, long error_code)
> >>  {
> >>  	DECLARE_BITMAP(valid_banks, MAX_NR_BANKS);
> >>  	DECLARE_BITMAP(toclear, MAX_NR_BANKS);
> >> @@ -1360,6 +1366,7 @@ void do_machine_check(struct pt_regs *re
> >>  	ist_exit(regs);
> >>  }
> >>  EXPORT_SYMBOL_GPL(do_machine_check);
> >> +NOKPROBE_SYMBOL(do_machine_check);
> > 
> > That won't protect all the function called by do_machine_check(), right?
> > There are lots of them.
> > 
> 
> It at least means we can survive to run actual C code in
> do_machine_check(), which lets us try to mitigate this issue further.
> PeterZ has patches for that, and maybe this series fixes it later on.
> (I'm reading in order!)

Yeah, I don't cover that either. Making the kernel completely kprobe
safe is _lots_ more work I think.

We really need some form of automation for this :/ The current situation
is completely nonsatisfactory.