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

Mike Rapoport
2024-10-19T12:11:02Z

On Thu, Oct 17, 2024 at 10:17:12AM -0400, Steven Rostedt wrote:
> 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);

We can also pass mod to ftrace_modify_code_direct() and use that to
distinguish early boot and ftrace_module_init.
With this I get very similar numbers like with the static branch

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 8da0e66ca22d..859902dd06fc 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -111,17 +111,22 @@ static int ftrace_verify_code(unsigned long ip, const char *old_code)
*/
static int __ref
ftrace_modify_code_direct(unsigned long ip, const char *old_code,
- const char *new_code)
+ const char *new_code, struct module *mod)
{
int ret = ftrace_verify_code(ip, old_code);
if (ret)
return ret;

/* replace the text with the new text */
- if (ftrace_poke_late)
+ if (ftrace_poke_late) {
text_poke_queue((void *)ip, new_code, MCOUNT_INSN_SIZE, NULL);
- else
+ } else if (!mod) {
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);
+ }
return 0;
}

@@ -142,7 +147,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long ad
* just modify the code directly.
*/
if (addr == MCOUNT_ADDR)
- return ftrace_modify_code_direct(ip, old, new);
+ return ftrace_modify_code_direct(ip, old, new, mod);

/*
* x86 overrides ftrace_replace_code -- this function will never be used
@@ -161,7 +166,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
new = ftrace_call_replace(ip, addr);

/* Should only be called when module is loaded */
- return ftrace_modify_code_direct(rec->ip, old, new);
+ return ftrace_modify_code_direct(rec->ip, old, new, NULL);
}

/*

--
Sincerely yours,
Mike.