netdev - Re: [PATCH] wireguard: convert index_hashtable and pubkey

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Message-ID: <CAHmME9oSo=4BtfO+=327n=gsor5gWcvhzAMS_BpqQ-6=6yxVRA@mail.gmail.com>
Date:   Wed, 8 Sep 2021 13:27:12 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     someguy@...ective-light.com
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        WireGuard mailing list <wireguard@...ts.zx2c4.com>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] wireguard: convert index_hashtable and pubkey_hashtable
 into rhashtables

Hi Hamza,

Thanks for this patch. I have a few concerns/questions about it:

- What's performance like? Does the abstraction of rhashtable
introduce overhead? These are used in fast paths -- for every packet
-- so being quick is important.

- How does this interact with the timing side channel concerns in the
comment of the file? Will the time required to find an unused index
leak the number of items in the hash table? Do we need stochastic
masking? Or is the construction of rhashtable such that we always get
ball-park same time?

Thanks,
Jason