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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Alexandre Chartre <alexandre.chartre@oracle.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Brian Gerst <brgerst@gmail.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Will Deacon <will@kernel.org>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Wei Liu <wei.liu@kernel.org>,
        Michael Kelley <mikelley@microsoft.com>,
        Jason Chen CJ <jason.cj.chen@intel.com>,
        Zhao Yakui <yakui.zhao@intel.com>
Subject: Re: [patch V6 00/37] x86/entry: Rework leftovers and merge plan
In-Reply-To: <20200518160750.GA279861@hirez.programming.kicks-ass.net>
References: <20200515234547.710474468@linutronix.de> <20200518160750.GA279861@hirez.programming.kicks-ass.net>
Date:   Mon, 18 May 2020 20:53:49 +0200
Message-ID: <87h7wdvzuq.fsf@nanos.tec.linutronix.de>
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Peter Zijlstra <peterz@infradead.org> writes:
> So on top of you entry-v8-full; I had to chase one of those
> instrumentation_end() escapes an (extended) basic block chase (again!).
>  
> +#ifdef CONFIG_DEBUG_ENTRY

Why this? We lose the kprobes runtime protection that way.

> +/* Section for code which can't be instrumented at all */
> +#define noinstr								\
> +	noinline notrace __attribute((__section__(".noinstr.text")))
> +
>  /* Begin/end of an instrumentation safe region */
> -#define instrumentation_begin() ({						\
> +#define instrumentation_begin() ({					\
>  	asm volatile("%c0:\n\t"						\
>  		     ".pushsection .discard.instr_begin\n\t"		\
>  		     ".long %c0b - .\n\t"				\
>  		     ".popsection\n\t" : : "i" (__COUNTER__));

Nifty.

Thanks,

        tglx