netdev - Re: [PATCH] [v3] infiniband: i40iw, nes: don't use wall time for TCP sequence numbers

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Date:   Wed, 11 Jul 2018 12:26:06 -0600
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Faisal Latif <faisal.latif@...el.com>,
        Shiraz Saleem <shiraz.saleem@...el.com>,
        Doug Ledford <dledford@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Yuval Shaia <yuval.shaia@...cle.com>,
        Henry Orosco <henry.orosco@...el.com>,
        Tatyana Nikolova <tatyana.e.nikolova@...el.com>,
        Mustafa Ismail <mustafa.ismail@...el.com>,
        Jia-Ju Bai <baijiaju1990@...il.com>,
        Bart Van Assche <bart.vanassche@....com>,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH] [v3] infiniband: i40iw, nes: don't use wall time for TCP
 sequence numbers

On Mon, Jul 09, 2018 at 10:34:43AM +0200, Arnd Bergmann wrote:
> The nes infiniband driver uses current_kernel_time() to get a nanosecond
> granunarity timestamp to initialize its tcp sequence counters. This is
> one of only a few remaining users of that deprecated function, so we
> should try to get rid of it.
> 
> Aside from using a deprecated API, there are several problems I see here:
> 
> - Using a CLOCK_REALTIME based time source makes it predictable in
>   case the time base is synchronized.
> - Using a coarse timestamp means it only gets updated once per jiffie,
>   making it even more predictable in order to avoid having to access
>   the hardware clock source
> - The upper 2 bits are always zero because the nanoseconds are at most
>   999999999.
> 
> For the Linux TCP implementation, we use secure_tcp_seq(), which appears
> to be appropriate here as well, and solves all the above problems.
> 
> i40iw uses a variant of the same code, so I do that same thing there
> for ipv4. Unlike nes, i40e also supports ipv6, which needs to call
> secure_tcpv6_seq instead.
> 
> Acked-by: Shiraz Saleem <shiraz.saleem@...el.com>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> v2: use secure_tcpv6_seq for IPv6 support as suggested by Shiraz Saleem.
> v3: add a soft IPv6 dependency to prevent a link error with CONFIG_IPV6=m,
>     this now forces i40iw to be a module as well, add an IS_ENABLED()
>     check to avoid calling it when IPV6 is completely disabled.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/infiniband/hw/i40iw/Kconfig    |  1 +
>  drivers/infiniband/hw/i40iw/i40iw_cm.c | 26 +++++++++++++++++++++-----
>  drivers/infiniband/hw/nes/nes_cm.c     |  8 +++++---
>  net/core/secure_seq.c                  |  1 +
>  4 files changed, 28 insertions(+), 8 deletions(-)

Applied to for-next thanks

Jason