netdev - Re: Resource management for ndo_xdp_xmit (Was: [PATCH net] virtio_net: Account for tx bytes and packets on sending xdp

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Date:   Sat, 09 Feb 2019 17:56:51 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Saeed Mahameed <saeedm@...lanox.com>
Cc:     "brouer\@redhat.com" <brouer@...hat.com>,
        "hawk\@kernel.org" <hawk@...nel.org>,
        "virtualization\@lists.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "borkmann\@iogearbox.net" <borkmann@...earbox.net>,
        Tariq Toukan <tariqt@...lanox.com>,
        "john.fastabend\@gmail.com" <john.fastabend@...il.com>,
        "mst\@redhat.com" <mst@...hat.com>,
        "dsahern\@gmail.com" <dsahern@...il.com>,
        "netdev\@vger.kernel.org" <netdev@...r.kernel.org>,
        "jasowang\@redhat.com" <jasowang@...hat.com>,
        "davem\@davemloft.net" <davem@...emloft.net>,
        "makita.toshiaki\@lab.ntt.co.jp" <makita.toshiaki@....ntt.co.jp>
Subject: Re: Resource management for ndo_xdp_xmit (Was: [PATCH net] virtio_net: Account for tx bytes and packets on sending xdp_frames)

Jakub Kicinski <jakub.kicinski@...ronome.com> writes:

> On Sat, 9 Feb 2019 00:18:31 +0000, Saeed Mahameed wrote:
>> On Fri, 2019-02-08 at 15:17 -0800, Saeed Mahameed wrote:
>> > On Thu, 2019-02-07 at 19:08 +0000, Saeed Mahameed wrote:  
>> > > 
>> > > So 
>> > > 1) on dev_map_update_elem() we will call
>> > > dev->dev->ndo_bpf() to notify the device on the intention to
>> > > start/stop
>> > > redirect, and wait for it to create/destroy the HW resources
>> > > before/after actually updating the map
>> > >   
>> > 
>> > silly me, dev_map_update_elem must be atomic, we can't hook driver
>> > resource allocation to it, it must come as a separate request
>> > (syscall)
>> > from user space to request to create XDP redirect resources.
>> >   
>> 
>> Well, it is possible to render dev_map_update_elem non-atomic and fail
>> BPF programs who try to update it in the verifier
>> check_map_func_compatibility.
>> 
>> if you know of any case where devmap needs to be updated from the BPF
>> program please let me know.
>
> Did we find a solution to non-map redirect?

See my other reply to Saeed :)

-Toke