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

Steven Rostedt
2024-10-17T14:16:56Z

On Wed, 16 Oct 2024 17:01:28 -0400
Steven Rostedt <rostedt@goodmis.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;
}