Re: [PATCH] Add static_key_feature_checks_initialized flag

[Nicholas Miehlbradt <nicholas@linux.ibm.com>]

On 28/3/2024 2:20 am, Christophe Leroy wrote:
> 
> 
> Le 27/03/2024 à 05:59, Nicholas Miehlbradt a écrit :
>> JUMP_LABEL_FEATURE_CHECK_DEBUG used static_key_initialized to determine
>> whether {cpu,mmu}_has_feature() was used before static keys were
>> initialized. However, {cpu,mmu}_has_feature() should not be used before
>> setup_feature_keys() is called. As static_key_initalized is set much
>> earlier during boot there is a window in which JUMP_LABEL_FEATURE_CHECK_DEBUG
>> will not report errors. Add a flag specifically to indicate when
>> {cpu,mmu}_has_feature() is safe to use.
> 
> What do you mean by "much earlier" ?
> 
> As far as I can see, static_key_initialized is set by jump_label_init()
> as cpu_feature_keys_init() and mmu_feature_keys_init() are call
> immediately after. I don't think it is possible to do anything inbetween.
> 
> Or maybe you mean the problem is the call to jump_label_init() in
> early_init_devtree() ? You should make it explicit in the message, and
> see if it wouldn't be better to call cpu_feature_keys_init() and
> mmu_feature_keys_init() as well in early_init_devtree() in that case ?
> 
The jump_label_init() call in early_init_devtree() is exactly the issue. 
I don't think it's possible to move the call to mmu_feature_keys_init() 
earlier without significant refactoring since mmu features are being set 
as late as setup_kup().

I'll still sent a v2 with a better worded commit message.

Nicholas

> Christophe