linux-kernel - Re: [RFC PATCH v2 13/20] context_tracking: Make context_tracking_key __ro_after

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Date:   Mon, 31 Jul 2023 12:16:43 +0100
From:   Valentin Schneider <vschneid@...hat.com>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, kvm@...r.kernel.org, linux-mm@...ck.org,
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        Yair Podemsky <ypodemsk@...hat.com>
Subject: Re: [RFC PATCH v2 13/20] context_tracking: Make
 context_tracking_key __ro_after_init

On 28/07/23 11:00, Josh Poimboeuf wrote:
> On Thu, Jul 20, 2023 at 05:30:49PM +0100, Valentin Schneider wrote:
>> objtool now warns about it:
>>
>>   vmlinux.o: warning: objtool: enter_from_user_mode+0x4e: Non __ro_after_init static key "context_tracking_key" in .noinstr section
>>   vmlinux.o: warning: objtool: enter_from_user_mode+0x50: Non __ro_after_init static key "context_tracking_key" in .noinstr section
>>   vmlinux.o: warning: objtool: syscall_enter_from_user_mode+0x60: Non __ro_after_init static key "context_tracking_key" in .noinstr section
>>   vmlinux.o: warning: objtool: syscall_enter_from_user_mode+0x62: Non __ro_after_init static key "context_tracking_key" in .noinstr section
>>   [...]
>>
>> The key can only be enabled (and not disabled) in the __init function
>> ct_cpu_tracker_user(), so mark it as __ro_after_init.
>>
>> Signed-off-by: Valentin Schneider <vschneid@...hat.com>
>
> It's best to avoid temporarily introducing warnings.  Bots will
> rightfully complain about that.  This patch and the next one should come
> before the objtool patches.
>

Ack, I'll reverse the order of these.

> Also it would be helpful for the commit log to have a brief
> justification for the patch beyond "fix the objtool warning".  Something
> roughly like:
>
>   Soon, runtime-mutable text won't be allowed in .noinstr sections, so
>   that a code patching IPI to a userspace-bound CPU can be safely
>   deferred to the next kernel entry.
>
>   'context_tracking_key' is only enabled in __init ct_cpu_tracker_user().
>   Mark it as __ro_after_init.
>

Looks better indeed, thanks!

> --
> Josh