netdev - Re: [PATCH] net/mlx5: IPSec, fix 64-bit division correctly

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Date:   Mon, 10 Jul 2017 08:45:43 -0700
From:   Joe Perches <joe@...ches.com>
To:     Ilan Tayari <ilant@...lanox.com>, Arnd Bergmann <arnd@...db.de>,
        Saeed Mahameed <saeedm@...lanox.com>
Cc:     Matan Barak <matanb@...lanox.com>,
        Leon Romanovsky <leonro@...lanox.com>,
        Yossi Kuperman <yossiku@...lanox.com>,
        Yevgeny Kliteynik <kliteyn@...lanox.com>,
        Boris Pismenny <borisp@...lanox.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net/mlx5: IPSec, fix 64-bit division correctly

On Mon, 2017-07-10 at 10:24 +0000, Ilan Tayari wrote:
> > -----Original Message-----
> > From: Arnd Bergmann [mailto:arnd@...db.de]
> > Subject: [PATCH] net/mlx5: IPSec, fix 64-bit division correctly
> > 
> > The new IPSec offload code introduced a build error:
> > 
> > drivers/net/ethernet/mellanox/mlx5/core/en_accel/ipsec_rxtx.o: In function
> > `mlx5e_ipsec_build_inverse_table':
> > ipsec_rxtx.c:(.text+0x556): undefined reference
> > 
> > Another patch was added on top to fix the build error, but
> > that introduced a new bug, as we now use the remainder of
> > the division rather than the result.

Is it possible to return noise in mlx5e_ipsec_mss_inv ?

What clamps skb_shinfo(skb)->gso_size to MAX_LSO
(the size of inverse_table)?

#define MAX_LSO_MSS 2048
static __be16 mlx5e_ipsec_inverse_table[MAX_LSO_MSS];

static inline __be16 mlx5e_ipsec_mss_inv(struct sk_buff *skb)
{
	return mlx5e_ipsec_inverse_table[skb_shinfo(skb)->gso_size];
}