netdev - Re: [PATCH net-next v6 2/7] net: ethtool: add support for symmetric-xor RSS hash

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Date: Mon, 27 Nov 2023 07:21:47 -0700
From: Ahmed Zaki <ahmed.zaki@...el.com>
To: Jakub Kicinski <kuba@...nel.org>
CC: <netdev@...r.kernel.org>, <intel-wired-lan@...ts.osuosl.org>,
	<corbet@....net>, <jesse.brandeburg@...el.com>, <anthony.l.nguyen@...el.com>,
	<davem@...emloft.net>, <edumazet@...gle.com>, <pabeni@...hat.com>,
	<vladimir.oltean@....com>, <andrew@...n.ch>, <horms@...nel.org>,
	<mkubecek@...e.cz>, <willemdebruijn.kernel@...il.com>, <gal@...dia.com>,
	<alexander.duyck@...il.com>, <linux-doc@...r.kernel.org>, Wojciech Drewek
	<wojciech.drewek@...el.com>
Subject: Re: [PATCH net-next v6 2/7] net: ethtool: add support for
 symmetric-xor RSS hash



On 2023-11-21 16:33, Jakub Kicinski wrote:
> On Mon, 20 Nov 2023 13:56:09 -0700 Ahmed Zaki wrote:
>> + * @data: Extension for the RSS hash function. Valid values are one of the
>> + *	%RXH_HFUNC_*.
> 
> @data is way too generic. Can we call this key_xfrm? key_preproc?

We manipulate the "input data" (protocol fields) not the key. I will 
rename to "input_xfrm".

> 
>> +/* RSS hash function data
>> + * XOR the corresponding source and destination fields of each specified
>> + * protocol. Both copies of the XOR'ed fields are fed into the RSS and RXHASH
>> + * calculation.
>> + */
>> +#define	RXH_HFUNC_SYM_XOR	(1 << 0)
> 
> We need to mention somewhere that sym-xor is unsafe, per Alex's
> comments.

I already added the following in Documentation/networking/scaling.rst:

"The Symmetric-XOR" is a type of RSS algorithms that achieves this hash 
symmetry by XORing the input source and destination fields of the IP
and/or L4 protocols. This, however, results in reduced input entropy and
could potentially be exploited."


Or do you mean add it also to "uapi/linux/ethtool.h" ?


Will do the rest in the next version.