netdev - Re: [PATCH bpf-next v2] net: Don't call XDP_SETUP

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Date:   Sat, 17 Aug 2019 23:29:57 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Maxim Mikityanskiy <maximmi@...lanox.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>
Subject: Re: [PATCH bpf-next v2] net: Don't call XDP_SETUP_PROG when nothing
 is changed

On 8/14/19 4:34 PM, Maxim Mikityanskiy wrote:
> Don't uninstall an XDP program when none is installed, and don't install
> an XDP program that has the same ID as the one already installed.
> 
> dev_change_xdp_fd doesn't perform any checks in case it uninstalls an
> XDP program. It means that the driver's ndo_bpf can be called with
> XDP_SETUP_PROG asking to set it to NULL even if it's already NULL. This
> case happens if the user runs `ip link set eth0 xdp off` when there is
> no XDP program attached.
> 
> The symmetrical case is possible when the user tries to set the program
> that is already set.
> 
> The drivers typically perform some heavy operations on XDP_SETUP_PROG,
> so they all have to handle these cases internally to return early if
> they happen. This patch puts this check into the kernel code, so that
> all drivers will benefit from it.
> 
> Signed-off-by: Maxim Mikityanskiy <maximmi@...lanox.com>

Applied, thanks!