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Date:   Mon, 26 Nov 2018 17:08:37 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Josh Poimboeuf <jpoimboe@redhat.com>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Andy Lutomirski <luto@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Jason Baron <jbaron@akamai.com>, Jiri Kosina <jkosina@suse.cz>,
        David Laight <David.Laight@ACULAB.COM>,
        Borislav Petkov <bp@alien8.de>,
        Julia Cartwright <julia@ni.com>, Jessica Yu <jeyu@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v2 4/4] x86/static_call: Add inline static call
 implementation for x86-64
Message-ID: <20181126160837.GS2113@hirez.programming.kicks-ass.net>
References: <cover.1543200841.git.jpoimboe@redhat.com>
 <62188c62f6dda49ca2e20629ee8e5a62a6c0b500.1543200841.git.jpoimboe@redhat.com>
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On Mon, Nov 26, 2018 at 07:55:00AM -0600, Josh Poimboeuf wrote:
> +#ifdef CONFIG_HAVE_STATIC_CALL_INLINE
> +void arch_static_call_defuse_tramp(void *site, void *tramp)
> +{
> +	unsigned short opcode = INSN_UD2;
> +
> +	mutex_lock(&text_mutex);
> +	text_poke((void *)tramp, &opcode, 2);
> +	mutex_unlock(&text_mutex);
> +}
> +#endif

I would rather think that makes the trampoline _more_ dangerous, rather
than less so.

My dictionary sayeth:

  defuse: verb

    - remove the fuse from (an explosive device) in order to prevent it
      from exploding.

    - make (a situation) less tense or dangerous

patching in an UD2 seems to do the exact opposite.