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.