linux-kernel - RE: [PATCH] net/mlx5: IPSec, fix 64-bit division correctly

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Message-ID: <AM4PR0501MB19405DA4B7430E02897CF0B9DBA90@AM4PR0501MB1940.eurprd05.prod.outlook.com>
Date:   Mon, 10 Jul 2017 09:57:47 +0000
From:   Ilan Tayari <ilant@...lanox.com>
To:     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

> -----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.
> 
> This makes it use the correct helper function instead.
> 
> Fixes: 5dfd87b67cd9 ("net/mlx5: IPSec, Fix 64-bit division on 32-bit
> builds")
> Fixes: 2ac9cfe78223 ("net/mlx5e: IPSec, Add Innova IPSec offload TX data
> path")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/net/ethernet/mellanox/mlx5/core/en_accel/ipsec_rxtx.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_accel/ipsec_rxtx.c
> b/drivers/net/ethernet/mellanox/mlx5/core/en_accel/ipsec_rxtx.c
> index 7d06c673851a..4614ddfa91eb 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_accel/ipsec_rxtx.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_accel/ipsec_rxtx.c
> @@ -363,7 +363,6 @@ void mlx5e_ipsec_build_inverse_table(void)
>  {
>  	u16 mss_inv;
>  	u32 mss;
> -	u64 n;
> 
>  	/* Calculate 1/x inverse table for use in GSO data path.
>  	 * Using this table, we provide the IPSec accelerator with the value
> of
> @@ -373,8 +372,7 @@ void mlx5e_ipsec_build_inverse_table(void)
>  	 */
>  	mlx5e_ipsec_inverse_table[1] = htons(0xFFFF);
>  	for (mss = 2; mss < MAX_LSO_MSS; mss++) {
> -		n = 1ULL << 32;
> -		mss_inv = do_div(n, mss) >> 16;
> +		mss_inv = div_u64(1ULL << 32, mss) >> 16;

Thanks Arnd, 

:o
I'm surprised... let me check this...

>  		mlx5e_ipsec_inverse_table[mss] = htons(mss_inv);
>  	}
>  }
> --
> 2.9.0