Message-ID: <xhsmhy11dhnz8.mognet@vschneid-thinkpadt14sgen2i.remote.csb>
Date: Wed, 20 Nov 2024 17:24:59 +0100
From: Valentin Schneider <vschneid@...hat.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>
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Subject: Re: [RFC PATCH v3 06/15] jump_label: Add forceful jump label type

On 19/11/24 15:39, Josh Poimboeuf wrote:
> On Tue, Nov 19, 2024 at 04:34:53PM +0100, Valentin Schneider wrote:
>> Later commits will cause objtool to warn about non __ro_after_init static
>> keys being used in .noinstr sections in order to safely defer instruction
>> patching IPIs targeted at NOHZ_FULL CPUs.
>
> Don't we need similar checking for static calls?
>

/sifts through my notes throwing paper all around

Huh, I thought I had something, but no... Per the results they don't seem
to be flipped around as much as static keys, but they also end up in
text_poke_bp(), so yeah, we do. Welp, I'll add that to the list.

>> Two such keys currently exist: mds_idle_clear and __sched_clock_stable,
>> which can both be modified at runtime.
>
> Not sure if feasible, but it sure would be a lot simpler to just make
> "no noinstr patching" a hard rule and then convert the above keys (or at
> least their noinstr-specific usage) to regular branches.
>
> Then "no noinstr patching" could be unilaterally enforced in
> text_poke_bp().
>
>> diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
>> index f5a2727ca4a9a..93e729545b941 100644
>> --- a/include/linux/jump_label.h
>> +++ b/include/linux/jump_label.h
>> @@ -200,7 +200,8 @@ struct module;
>>  #define JUMP_TYPE_FALSE		0UL
>>  #define JUMP_TYPE_TRUE		1UL
>>  #define JUMP_TYPE_LINKED	2UL
>> -#define JUMP_TYPE_MASK		3UL
>> +#define JUMP_TYPE_FORCEFUL      4UL
>
> JUMP_TYPE_NOINSTR_ALLOWED ?
>

That's better, I'll take it. Thanks!

> -- 
> Josh

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