Subject: Re: [PATCH v7 0/8] x86/module: use large ROX pages for text allocations

From: Mike Rapoport <[email-masked]>
Date: Mon, 18 Nov 2024 10:40:26 -0800

On Mon, Nov 18, 2024 at 01:25:01PM -0500, Steven Rostedt wrote:
> On Wed, 23 Oct 2024 19:27:03 +0300
> Mike Rapoport <[email-masked]> wrote:
> 
> > From: "Mike Rapoport (Microsoft)" <[email-masked]>
> > 
> > Hi,
> > 
> > This is an updated version of execmem ROX caches.
> > 
> 
> FYI, I booted a kernel before and after applying these patches with my
> change:
> 
>   https://lore.kernel.org/[email-masked]
> 
> Before these patches:
> 
>  # cat /sys/kernel/tracing/dyn_ftrace_total_info
> 57695 pages:231 groups: 9
> ftrace boot update time = 14733459 (ns)
> ftrace module total update time = 449016 (ns)
> 
> After:
> 
>  # cat /sys/kernel/tracing/dyn_ftrace_total_info
> 57708 pages:231 groups: 9
> ftrace boot update time = 47195374 (ns)
> ftrace module total update time = 592080 (ns)
> 
> Which caused boot time to slowdown by over 30ms. That may not seem like
> much, but we are very concerned about boot time and are fighting every ms
> we can get.

Hmm, looks like this change was lost in rebase :/

@Andrew, should I send it as a patch on top of mm-stable?

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);
 }
 
 /*

> -- Steve

-- 
Sincerely yours,
Mike.