linux-kernel - Re: [PATCH v3 2/7] x86/jump_label: Use text_poke_early() during early

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Date:   Mon, 5 Nov 2018 15:09:25 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nadav Amit <namit@...are.com>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH v3 2/7] x86/jump_label: Use text_poke_early() during
 early_init

On Fri, Nov 02, 2018 at 04:29:41PM -0700, Nadav Amit wrote:
> diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
> index aac0c1f7e354..367c1d0c20a3 100644
> --- a/arch/x86/kernel/jump_label.c
> +++ b/arch/x86/kernel/jump_label.c
> @@ -52,7 +52,13 @@ static void __ref __jump_label_transform(struct jump_entry *entry,
>  	jmp.offset = jump_entry_target(entry) -
>  		     (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
>  
> -	if (early_boot_irqs_disabled)
> +	/*
> +	 * As long as we are in early boot, we can use text_poke_early(), which
> +	 * is more efficient: the memory was still not marked as read-only (it
> +	 * is only marked after poking_init()). This also prevents us from using
> +	 * text_poke() before poking_init() is called.
> +	 */
> +	if (!early_boot_done)
>  		poker = text_poke_early;
>  
>  	if (type == JUMP_LABEL_JMP) {

It took me a while to untangle init/maze^H^Hin.c... but I think this
is all we need:

diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index aac0c1f7e354..ed5fe274a7d8 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -52,7 +52,12 @@ static void __ref __jump_label_transform(struct jump_entry *entry,
 	jmp.offset = jump_entry_target(entry) -
 		     (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
 
-	if (early_boot_irqs_disabled)
+	/*
+	 * As long as we're UP and not yet marked RO, we can use
+	 * text_poke_early; SYSTEM_BOOTING guarantees both, as we switch to
+	 * SYSTEM_SCHEDULING before going either.
+	 */
+	if (system_state == SYSTEM_BOOTING)
 		poker = text_poke_early;
 
 	if (type == JUMP_LABEL_JMP) {