Symbol cpu_feature_keys should be exported to all modules on powerpc

Symbol cpu_feature_keys should be exported to all modules on powerpc

[王昊然]

Just like symbol 'mmu_feature_keys'[1], 'cpu_feature_keys' was referenced
indirectly by many inline functions; any GPL-incompatible modules using such
a function will be potentially broken due to 'cpu_feature_keys' being
exported as GPL-only.

For example it still breaks ZFS, see
https://github.com/openzfs/zfs/issues/14545

[1]: https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20220329085709.4132729-1-haokexin@gmail.com/

Re: Symbol cpu_feature_keys should be exported to all modules on powerpc

[Greg KH]

On Tue, Feb 28, 2023 at 04:18:12PM +0800, 王昊然 wrote:
> Just like symbol 'mmu_feature_keys'[1], 'cpu_feature_keys' was referenced
> indirectly by many inline functions; any GPL-incompatible modules using such
> a function will be potentially broken due to 'cpu_feature_keys' being
> exported as GPL-only.
> 
> For example it still breaks ZFS, see
> https://github.com/openzfs/zfs/issues/14545
> 
> [1]: https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20220329085709.4132729-1-haokexin@gmail.com/

External modules are always on their own, sorry.  Especially ones that
are not released under the GPL.

good luck!

greg k-h

Fwd: Symbol cpu_feature_keys should be exported to all modules on powerpc

[王昊然]

---------- Forwarded message ----------
From: 王昊然 <msl0000023508@gmail.com>
Date: Tue, 28 Feb 2023 18:16:14 +0800
Subject: Re: Symbol cpu_feature_keys should be exported to all modules
on powerpc
To: Greg KH <gregkh@linuxfoundation.org>
Cc: stable@vger.kernel.org

2023-02-28 16:28 GMT+08:00, Greg KH <gregkh@linuxfoundation.org>:
> On Tue, Feb 28, 2023 at 04:18:12PM +0800, 王昊然 wrote:
>> Just like symbol 'mmu_feature_keys'[1], 'cpu_feature_keys' was referenced
>> indirectly by many inline functions; any GPL-incompatible modules using
>> such
>> a function will be potentially broken due to 'cpu_feature_keys' being
>> exported as GPL-only.
>>
>> For example it still breaks ZFS, see
>> https://github.com/openzfs/zfs/issues/14545
>>
>> [1]:
>> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20220329085709.4132729-1-haokexin@gmail.com/
>
> External modules are always on their own, sorry.  Especially ones that
> are not released under the GPL.
>
> good luck!
>
> greg k-h
>

Some inline functions are just powerpc implementation of some generic KPIs,
such as flush_dcache_page, which indirectly references 'cpu_feature_keys' in
powerpc-specific code; this essentially makes 'flush_dcache_page' GPL-only in
Linux powerpc, but not in other architectures.