linux-kernel - Re: [PATCH V4 2/9] jump_label: Add the jump_label_can_update

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Date:   Tue, 5 Feb 2019 08:22:20 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Daniel Bristot de Oliveira <bristot@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Jiri Kosina <jkosina@...e.cz>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Chris von Recklinghausen <crecklin@...hat.com>,
        Jason Baron <jbaron@...mai.com>, Scott Wood <swood@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Clark Williams <williams@...hat.com>, x86@...nel.org
Subject: Re: [PATCH V4 2/9] jump_label: Add the jump_label_can_update_check()
 helper

> Subject: Re: [PATCH V4 2/9] jump_label: Add the jump_label_can_update_check() helper

s/the/a/

On Mon, Feb 04, 2019 at 08:58:55PM +0100, Daniel Bristot de Oliveira wrote:
> Move the check of if a jump_entry is valid to a function.

s/of //

> diff --git a/kernel/jump_label.c b/kernel/jump_label.c
> index 288d630da22d..456c0d7cbb5b 100644
> --- a/kernel/jump_label.c
> +++ b/kernel/jump_label.c
> @@ -374,22 +374,32 @@ static enum jump_label_type jump_label_type(struct jump_entry *entry)
>  	return enabled ^ branch;
>  }
>  
> +bool jump_label_can_update_check(struct jump_entry *entry, bool init)

static.

Also, "jump_label_can_update" is sufficient for a name AFAICT.

> +{
> +	/*
> +	 * An entry->code of 0 indicates an entry which has been
> +	 * disabled because it was in an init text area.
> +	 */
> +	if (init || !jump_entry_is_init(entry)) {
> +		if (!kernel_text_address(jump_entry_code(entry))) {
> +			WARN_ONCE(1, "can't patch jump_label at %pS",
> +				  (void *)jump_entry_code(entry));
> +			return 0;
> +		}
> +		return 1;
> +	}
> +	return 0;

Those should be bools which it returns, no?

Also, I'd do the function this way, to make it more readable and not
have three returns back-to-back. :)

/*
 * An entry->code of 0 indicates an entry which has been disabled because it
 * was in an init text area.
 */
bool jump_label_can_update(struct jump_entry *entry, bool init)
{
        if (!init && jump_entry_is_init(entry))
                return false;

        if (WARN_ON_ONCE(!kernel_text_address(jump_entry_code(entry))),
                         "can't patch jump_label at %pS", (void *)jump_entry_code(entry))
                return false;

        return true;
}

That second check could be even:

        if (WARN_ON_ONCE(!kernel_text_address(jump_entry_code(entry))),
                         "can't patch jump_label at %pS", (void *)jump_entry_code(entry))
                return false;

but that's not more readable than above, I'd say.

>  static void __jump_label_update(struct static_key *key,
>  				struct jump_entry *entry,
>  				struct jump_entry *stop,
>  				bool init)
>  {
>  	for_each_label_entry(key, entry, stop) {
> -		/*
> -		 * An entry->code of 0 indicates an entry which has been
> -		 * disabled because it was in an init text area.
> -		 */
> -		if (init || !jump_entry_is_init(entry)) {
> -			if (kernel_text_address(jump_entry_code(entry)))
> -				arch_jump_label_transform(entry, jump_label_type(entry));
> -			else
> -				WARN_ONCE(1, "can't patch jump_label at %pS",
> -					  (void *)jump_entry_code(entry));
> +		if (jump_label_can_update_check(entry, init)) {
> +			arch_jump_label_transform(entry,
> +						  jump_label_type(entry));

Yeah, let that one stick out.

-- 
Regards/Gruss,
    Boris.

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