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

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Date:   Wed, 14 Aug 2019 10:57:19 -0700
From:   "Jonathan Lemon" <jlemon@...gsvamp.com>
To:     "Maxim Mikityanskiy" <maximmi@...lanox.com>
Cc:     "Alexei Starovoitov" <ast@...nel.org>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        "Jakub Kicinski" <jakub.kicinski@...ronome.com>,
        bpf@...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 14 Aug 2019, at 7:34, 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>

Acked-by: Jonathan Lemon <jonathan.lemon@...il.com>