Re: [PATCH 05/11] x86/fpu: set PKRU state for kernel threads

[Dave Hansen]

On 10/04/2018 07:05 AM, Sebastian Andrzej Siewior wrote:
> The PKRU value is not set for kernel threads because they do not have
> the ->initialized value set. As a result the kernel thread has a random
> PKRU value set which it inherits from the previous task.
> It has been suggested by Paolo Bonzini to set it for kernel threads, too
> because it might be a fix.
> I *think* this is not required because the kernel threads don't copy
> data to/from userland and don't have access to any userspace mm in
> general.
> However there is this use_mm(). If we gain a mm by use_mm() we don't
> have a matching PKRU value because those are per thread. It has been
> suggested to use 0 as the PKRU value but this would bypass PKRU.
> 
> Set the initial (default) PKRU value for kernel threads.

We might want to do this for cleanliness reasons...  Maybe.

But this *should* have no practical effects.  Kernel threads have no
real 'mm' and no user pages.  They should not have do access to user
mappings.  Protection keys *only* apply to user mappings.  Thus,
logically, they should never be affected by PKRU values.

So I'm kinda missing the point of the patch.