linux-kernel - Re: [PATCH v6 6/8] x86/module: prepare module loading for ROX allocations of text

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Message-ID: <20241017101712.5a052712@gandalf.local.home>
Date: Thu, 17 Oct 2024 10:17:12 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Mike Rapoport <rppt@...nel.org>
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Subject: Re: [PATCH v6 6/8] x86/module: prepare module loading for ROX
 allocations of text

On Wed, 16 Oct 2024 17:01:28 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> If this is only needed for module load, can we at least still use the
> text_poke_early() at boot up?
> 
>  	if (ftrace_poke_late) {
>  		text_poke_queue((void *)ip, new_code, MCOUNT_INSN_SIZE, NULL);
> 	} else if (system_state == SYSTEM_BOOTING) {
> 		text_poke_early((void *)ip, new_code, MCOUNT_INSN_SIZE);
>  	} else {
>  		mutex_lock(&text_mutex);
>  		text_poke((void *)ip, new_code, MCOUNT_INSN_SIZE);
>  		mutex_unlock(&text_mutex);
>  	}
> 
> ?
> 
> The above if statement looks to slow things down just slightly, but only by
> 2ms, which is more reasonable.

I changed the above to this (yes it's a little hacky) and got my 2ms back!

-- Steve

DEFINE_STATIC_KEY_TRUE(ftrace_modify_boot);

static int __init ftrace_boot_init_done(void)
{
	static_branch_disable(&ftrace_modify_boot);
	return 0;
}
/* Ftrace updates happen before core init */
core_initcall(ftrace_boot_init_done);

/*
 * Marked __ref because it calls text_poke_early() which is .init.text. That is
 * ok because that call will happen early, during boot, when .init sections are
 * still present.
 */
static int __ref
ftrace_modify_code_direct(unsigned long ip, const char *old_code,
			  const char *new_code)
{
	int ret = ftrace_verify_code(ip, old_code);

	if (ret)
		return ret;

	/* replace the text with the new text */
	if (static_branch_unlikely(&ftrace_modify_boot)) {
		text_poke_early((void *)ip, new_code, MCOUNT_INSN_SIZE);
	} else if (ftrace_poke_late) {
		text_poke_queue((void *)ip, new_code, MCOUNT_INSN_SIZE, NULL);
	} else {
		mutex_lock(&text_mutex);
		text_poke((void *)ip, new_code, MCOUNT_INSN_SIZE);
		mutex_unlock(&text_mutex);
	}
	return 0;
}