Re: [RFC PATCH v2 13/20] context_tracking: Make context_tracking_key __ro_after_init

Valentin Schneider
2023-07-31T11:17:50Z

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@redhat.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