Hi, > I may miss something. > > But RSS requires to update the map. This won't work if you don't grant > any permission to qemu. > > Thanks >
Partly - with "kernel.unprivileged_bpf_disabled=0" capabilities is not required to update maps. With "kernel.unprivileged_bpf_disabled=1" - setting maps will fail(without CAP_BPF) and "in-qemu" RSS will be used. On Tue, Jun 15, 2021 at 12:13 PM Jason Wang <jasow...@redhat.com> wrote: > > 在 2021/6/12 上午12:49, Andrew Melnichenko 写道: > > Hi, > > > > 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. > > > > > > The main idea is to run eBPF RSS with qemu without any permission. > > Libvirt should handle everything and pass proper eBPF file descriptors. > > For current eBPF RSS, CAP_SYS_ADMIN(bypass some limitations) > > also required, and in the future may be other permissions. > > > I may miss something. > > But RSS requires to update the map. This won't work if you don't grant > any permission to qemu. > > Thanks > > > > > > 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 > > > > > > Technically TAP/vhost not related to a particular qemu emulator. So > common > > TAP creation should fit any modern qemu. eBPF fds(program and maps) > should > > suit the interface for current qemu, g.e. some qemu builds may have > > different map > > structures or their count. It's necessary that the qemu got fds > > prepared by the helper > > that was built with the qemu. > > > > I think we need an example on the detail steps for how libvirt is > > expected to use this. > > > > > > The simplified workflow looks like this: > > > > 1. Libvirt got "emulator" from domain document. > > 2. Libvirt queries for qemu capabilities. > > 3. One of the capabilities is "qemu-ebpf-rss-helper" path(if present). > > 4. On NIC preparation Libvirt checks for virtio-net + rss > configurations. > > 5. If required, the "qemu-ebpf-rss-helper" called and fds are > > received through unix fd. > > 6. Those fds are for eBPF RSS, which passed to child process - qemu. > > 7. Qemu launched with virtio-net-pci property "rss" and "ebpf_rss_fds". > > > > > > On Fri, Jun 11, 2021 at 8:36 AM Jason Wang <jasow...@redhat.com > > <mailto:jasow...@redhat.com>> wrote: > > > > > > 在 2021/6/10 下午2:55, Yuri Benditovich 写道: > > > On Thu, Jun 10, 2021 at 9:41 AM Jason Wang<jasow...@redhat.com > > <mailto:jasow...@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 > > <https://github.com/daynix/libvirt/tree/RSSv1> > > > > > > Will have a look but it would be better if the assumption of the > > management is detailed here to ease the reviewers. > > > > Thanks > > > > > > > > > > >
