Re: [RFC PATCH 0/5] ebpf: Added ebpf helper for libvirtd.

[Yuri Benditovich]

On Thu, Jun 10, 2021 at 9:41 AM Jason Wang <jasowang@redhat.com> wrote:
>
>
> 在 2021/6/9 下午6:04, Andrew Melnychenko 写道:
> > Libvirt usually launches qemu with strict permissions.
> > To enable eBPF RSS steering, qemu-ebpf-rss-helper was added.
>
>
> A silly question:
>
> Kernel had the following permission checks in bpf syscall:
>
>         if (sysctl_unprivileged_bpf_disabled && !bpf_capable())
>                  return -EPERM;
> ...
>
>          err = security_bpf(cmd, &attr, size);
>          if (err < 0)
>                  return err;
>
> So if I understand the code correctly, bpf syscall can only be done if:
>
> 1) unprivileged_bpf is enabled or
> 2) has the capability  and pass the LSM checks
>
> So I think the series is for unprivileged_bpf disabled. If I'm not
> wrong, I guess the policy is to grant CAP_BPF but do fine grain checks
> via LSM.
>
> If this is correct, need to describe it in the commit log.
>
>
> >
> > Added property "ebpf_rss_fds" for "virtio-net" that allows to
> > initialize eBPF RSS context with passed program & maps fds.
> >
> > Added qemu-ebpf-rss-helper - simple helper that loads eBPF
> > context and passes fds through unix socket.
> > Libvirt should call the helper and pass fds to qemu through
> > "ebpf_rss_fds" property.
> >
> > Added explicit target OS check for libbpf dependency in meson.
> > eBPF RSS works only with Linux TAP, so there is no reason to
> > build eBPF loader/helper for non-Linux.
> >
> > Overall, libvirt process should not be aware of the "interface"
> > of eBPF RSS, it will not be aware of eBPF maps/program "type" and
> > their quantity.
>
>
> I'm not sure this is the best. We have several examples that let libvirt
> to involve. Examples:
>
> 1) create TAP device (and the TUN_SETIFF)
>
> 2) open vhost devices
>
>
> >   That's why qemu and the helper should be from
> > the same build and be "synchronized". Technically each qemu may
> > have its own helper. That's why "query-helper-paths" qmp command
> > was added. Qemu should return the path to the helper that suits
> > and libvirt should use "that" helper for "that" emulator.
> >
> > qmp sample:
> > C: { "execute": "query-helper-paths" }
> > S: { "return": [
> >       {
> >         "name": "qemu-ebpf-rss-helper",
> >         "path": "/usr/local/libexec/qemu-ebpf-rss-helper"
> >       }
> >      ]
> >     }
>
>
> I think we need an example on the detail steps for how libvirt is
> expected to use this.

The preliminary patches for libvirt are at
https://github.com/daynix/libvirt/tree/RSSv1

>
> Thanks
>
>
> >
> > Andrew Melnychenko (5):
> >    ebpf: Added eBPF initialization by fds.
> >    virtio-net: Added property to load eBPF RSS with fds.
> >    ebpf_rss_helper: Added helper for eBPF RSS.
> >    qmp: Added qemu-ebpf-rss-path command.
> >    meson: libbpf dependency now exclusively for Linux.
> >
> >   ebpf/ebpf_rss-stub.c           |   6 ++
> >   ebpf/ebpf_rss.c                |  31 +++++++-
> >   ebpf/ebpf_rss.h                |   5 ++
> >   ebpf/qemu-ebpf-rss-helper.c    | 130 +++++++++++++++++++++++++++++++++
> >   hw/net/virtio-net.c            |  77 ++++++++++++++++++-
> >   include/hw/virtio/virtio-net.h |   1 +
> >   meson.build                    |  37 ++++++----
> >   monitor/qmp-cmds.c             |  78 ++++++++++++++++++++
> >   qapi/misc.json                 |  29 ++++++++
> >   9 files changed, 374 insertions(+), 20 deletions(-)
> >   create mode 100644 ebpf/qemu-ebpf-rss-helper.c
> >
>