netdev - Re: recvfrom/recvmsg performance and CONFIG_HARDENED

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Message-ID: <fbac8306-247f-10f3-4067-14c0610b17d6@gmail.com>
Date:   Fri, 6 Dec 2019 08:19:03 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        David Laight <David.Laight@...LAB.COM>,
        network dev <netdev@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: recvfrom/recvmsg performance and CONFIG_HARDENED_USERCOPY



On 12/6/19 8:09 AM, Paolo Abeni wrote:

> Oh, nice! I though the compiler was smart enough to avoid the indirect
> call with the current code, but it looks like that least gcc 9.2.1 is
> not.
> 
> Thanks for pointing that out!
> 
> In this specific scenario I think the code you propose above is better
> than INDIRECT_CALL.
> 
> Would you submit the patch formally?

Certainly, although I am not sure this will be enough to close
the gap between recvmsg() and recvfrom() :)

Also I was wondering if a likely() or unlikely() clause would
make sense.

This could prevent an over zealous compiler optimizer
to put back the indirect call that we tried to avoid.