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From:   Andy Lutomirski <luto@amacapital.net>
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Subject: Re: [patch 02/10] x86/mce: Disable tracing and kprobes on do_machine_check()
Date:   Wed, 26 Feb 2020 11:09:03 -0800
Message-Id: <F7C318D0-D9B8-4984-AE84-2E903837EED5@amacapital.net>
References: <20200226185945.GC18400@hirez.programming.kicks-ass.net>
Cc:     Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>, X86 ML <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>
In-Reply-To: <20200226185945.GC18400@hirez.programming.kicks-ass.net>
To:     Peter Zijlstra <peterz@infradead.org>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Feb 26, 2020, at 10:59 AM, Peter Zijlstra <peterz@infradead.org> wrote:=

>=20
> =EF=BB=BFOn 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.
>>=20
>> FWIW, I had this at the beginning of the #MC handler in a feeble attempt
>> to poke at this:
>>=20
>> +       hw_breakpoint_disable();
>> +       static_key_disable(&__tracepoint_read_msr.key);
>> +       tracing_off();
>=20
> You can't do static_key_disable() from an IST

Can we set a percpu variable saying =E2=80=9Cin some stupid context, don=E2=80=
=99t trace=E2=80=9D?=