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

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Date:   Thu, 7 Feb 2019 18:00:53 +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

On 2/7/19 3:08 PM, Borislav Petkov wrote:
> On Thu, Feb 07, 2019 at 02:21:09PM +0100, Daniel Bristot de Oliveira wrote:
>> diff --git a/kernel/jump_label.c b/kernel/jump_label.c
>> index 288d630da22d..1e6f4d27e28d 100644
>> --- a/kernel/jump_label.c
>> +++ b/kernel/jump_label.c
>> @@ -374,22 +374,29 @@ static enum jump_label_type jump_label_type(struct jump_entry *entry)
>>  	return enabled ^ branch;
>>  }
>>  
>> +static bool jump_label_can_update(struct jump_entry *entry, bool init)
>> +{
>> +	/*
>> +	 * Cannot update code that was in an init text area.
>> +	 */
>> +	if (!init || jump_entry_is_init(entry))
> 
> Shouldn't this be &&
> 
> ?

Oops! should be &&! sorry.

>> +		return false;
>> +
>> +	if (WARN_ONCE(!kernel_text_address(jump_entry_code(entry)),
>> +			 "can't patch jump_label at %pS", (void *)jump_entry_code(entry)))
>> +		return false;
> 
> Yeah, I think that this way of writing it is less readable than:
> 
> 	if (!kernel_text_address(jump_entry_code(entry))) {
> 		WARN_ONCE(1, "can't patch jump_label at %pS", (void *)jump_entry_code(entry));
> 		return false;
> 	}

It is taking 95 characters. In this case, wouldn't be better to break?

        if (!kernel_text_address(jump_entry_code(entry))) {
                WARN_ONCE(1, "can't patch jump_label at %pS",
                          (void *)jump_entry_code(entry));
                return false;
        }

I agree your suggestion is better... just confirming that 95 is not too long...

> 
>> +		if (jump_label_can_update(entry, init)) {
>> +			arch_jump_label_transform(entry, jump_label_type(entry));
> 
> Yap.
> 
> Thx.
> 

Thanks!

-- Daniel