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

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Message-ID: <cb65e500-44dd-873c-622f-b49b9336b6a2@redhat.com>
Date:   Tue, 5 Feb 2019 14:50:39 +0100
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
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

Hi Borislav!

On 2/5/19 8:22 AM, Borislav Petkov wrote:
>> Subject: Re: [PATCH V4 2/9] jump_label: Add the jump_label_can_update_check() helper
> 
> s/the/a/

ack!

> 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 //

ack!

>> 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.

sounds better indeed.

>> +{
>> +	/*
>> +	 * 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.

Agreed!

> 
>>  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.

I did not get this part...

Thanks!

-- Daniel