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

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Date:   Fri, 14 Oct 2016 12:11:12 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        "linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Network Development <netdev@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Linux Wireless List <linux-wireless@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jouni Malinen <j@...fi>
Subject: Re: [mac80211] BUG_ON with current -git (4.8.0-11417-g24532f7)

On 14 October 2016 at 11:00, Johannes Berg <johannes@...solutions.net> 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.