netdev - Re: [PATCH net-next V2 3/3] tun: add eBPF based queue selection method

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Date:   Wed, 8 Nov 2017 20:13:15 +0900
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Tom Herbert <tom@...bertland.com>,
        Aaron Conole <aconole@...hat.com>
Subject: Re: [PATCH net-next V2 3/3] tun: add eBPF based queue selection
 method



On 2017年11月08日 14:43, Michael S. Tsirkin wrote:
> On Wed, Nov 08, 2017 at 02:28:53PM +0900, Jason Wang wrote:
>>
>> On 2017年11月04日 08:56, Willem de Bruijn wrote:
>>> On Fri, Nov 3, 2017 at 5:56 PM, Willem de Bruijn
>>> <willemdebruijn.kernel@...il.com> wrote:
>>>> On Tue, Oct 31, 2017 at 7:32 PM, Jason Wang <jasowang@...hat.com> wrote:
>>>>> This patch introduces an eBPF based queue selection method based on
>>>>> the flow steering policy ops. Userspace could load an eBPF program
>>>>> through TUNSETSTEERINGEBPF. This gives much more flexibility compare
>>>>> to simple but hard coded policy in kernel.
>>>>>
>>>>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>>>>> ---
>>>>> +static int tun_set_steering_ebpf(struct tun_struct *tun, void __user *data)
>>>>> +{
>>>>> +       struct bpf_prog *prog;
>>>>> +       u32 fd;
>>>>> +
>>>>> +       if (copy_from_user(&fd, data, sizeof(fd)))
>>>>> +               return -EFAULT;
>>>>> +
>>>>> +       prog = bpf_prog_get_type(fd, BPF_PROG_TYPE_SOCKET_FILTER);
>>>> If the idea is to allow guests to pass BPF programs down to the host,
>>>> you may want to define a new program type that is more restrictive than
>>>> socket filter.
>>>>
>>>> The external functions allowed for socket filters (sk_filter_func_proto)
>>>> are relatively few (compared to, say, clsact), but may still leak host
>>>> information to a guest. More importantly, guest security considerations
>>>> limits how we can extend socket filters later.
>>> Unless the idea is for the hypervisor to prepared the BPF based on a
>>> limited set of well defined modes that the guest can configure. Then
>>> socket filters are fine, as the BPF is prepared by a regular host process.
>> Yes, I think the idea is to let qemu to build a BPF program now.
>>
>> Passing eBPF program from guest to host is interesting, but an obvious issue
>> is how to deal with the accessing of map.
>>
>> Thanks
> Fundamentally, I suspect the way to solve it is to allow
> the program to specify "should be offloaded to host".
>
> And then it would access the host map rather than the guest map.

This looks a big extension.

>
> Then add some control path API for guest to poke at the host map.

Actually, as Willem said, we can even forbid using map through a type, 
but this will lose lots of flexibility.

>
> It's not that there's anything special about the host map -
> it's just separate from the guest - so if we wanted to
> do something that can work on bare-metal we could -
> just do something like a namespace and put all host
> maps there. But I'm not sure it's worth the complexity.
>
> Cc Aaron who wanted to look at this.
>

Maybe the first step is to let classic BPF to be passed from guest and 
consider eBPF on top.

Thanks