Re: [mac80211] BUG_ON with current -git (4.8.0-11417-g24532f7)

From: Ard Biesheuvel
Date: Fri Oct 14 2016 - 07:11:31 EST

On 14 October 2016 at 11:00, Johannes Berg <johannes@xxxxxxxxxxxxxxxx> wrote:
>> So why is the performance hit acceptable for ESP but not for WPA? We
>> could easily implement the same thing, i.e.,
>> kmalloc(GFP_ATOMIC)/kfree the aead_req struct rather than allocate it
>> on the stack
> Yeah, maybe we should. It's likely a much bigger allocation, but I
> don't actually know if that affects speed.
> In most cases where you want high performance we never hit this anyway
> since we'll have hardware crypto. I know for our (Intel's) devices we
> normally never hit these code paths.
> But on the other hand, you also did your changes for a reason, and the
> only reason I can see of that is performance. So you'd be the one with
> most "skin in the game", I guess?

Well, what sucks here is that the accelerated driver I implemented for
arm64 does not actually need this, as long as we take aad[] off the
stack. And note that the API was changed since my patch, to add aad[]
to the scatterlist: prior to this change, it used
aead_request_set_assoc() to set the associated data separately.