[RFC PATCH 1/9] kernel: add support for patchable function pointers

[Ard Biesheuvel]

> On 5 Oct 2018, at 20:28, Jason A. Donenfeld <Jason at zx2c4.com> wrote:
> 
> Hey Andy,
> 
>> On Fri, Oct 5, 2018 at 7:44 PM Andy Lutomirski <luto at kernel.org> wrote:
>> I *think* the only change to Zinc per se would be that the calls like
>> chacha20_simd() would be static calls or patchable functions or
>> whatever we want to call them.  And there could be a debugfs to
>> override the default selection.
> 
> Yea, right, exactly. It turns out this is really easy to do with the
> way it's structured now. I'd actually experimented considerably with
> using the static keys a while back, but couldn't find any performance
> difference on any platform at all (four ARM microarchitectures, three
> MIPS, various random intel, an old powerpc), so went with the simplest
> solution. But we can certainly play with more elaborate patching
> mechanisms later on and see how those turn out. Also, even with the
> simple bools as we have now, it's quite easy to make all the
> parameters toggle-able.
> 
>> Ard, I don't think that sticking this in udev rules makes sense.  The
>> kernel has bascially complete information as to what the right choice
>> is, and that will change over time as the implementation gets tuned,
>> and the udev rules will never get updated in sync.
> 
> Yes, I agree with this.
> 
> 

I am not referring to udev rules. I just mean the current way that udev autoloads modules based on CPU features.