Re: [PATCH 4/5] ebpf_rss_helper: Added helper for eBPF RSS.

[Andrew Melnichenko]

Hi,

I think it's for back-compatibility.

E.g current codes works without mmap(), and user will surprise that it
wont' work after upgrading their qemu.

Well, the current code would require additional capabilities with "kernel.unprivileged_bpf_disabled=1", which may be possible on RedHat systems.

Technically we may have mmap test which will show that mmap for BPF_MAP_TYPE_ARRAY works, but on the target system, we will know it only in runtime.

If I'm not mistaken, mmap for BPF_MAP_TYPE_ARRAY was added before kernel 5.4 and our bpf program requires kernel 5.8+.

So, there are no reasons to add bpf() update map as a fallback for mmap().

On Wed, Sep 1, 2021 at 9:42 AM Jason Wang <jasowang@redhat.com> wrote:

在 2021/8/31 上午1:07, Yuri Benditovich 写道:
> On Fri, Aug 20, 2021 at 6:41 AM Jason Wang <jasowang@redhat.com> wrote:
>>
>> 在 2021/7/13 下午11:37, Andrew Melnychenko 写道:
>>> Helper program. Loads eBPF RSS program and maps and passes them through unix socket.
>>> Libvirt may launch this helper and pass eBPF fds to qemu virtio-net.
>>
>> I wonder if this can be done as helper for TAP/bridge.
>>
>> E.g it's the qemu to launch those helper with set-uid.
>>
>> Then libvirt won't even need to care about that?
>>
> There are pros and cons for such a solution with set-uid.
>  From my point of view one of the cons is that set-uid is efficient
> only at install time so the coexistence of different qemu builds (and
> different helpers for each one) is kind of problematic.
> With the current solution this does not present any problem: the
> developer can have several different builds, each one automatically
> has its own helper and there is no conflict between these builds and
> between these builds and installed qemu package. Changing the
> 'emulator' in the libvirt profile automatically brings the proper
> helper to work.


I'm not sure I get you here. We can still have default/sample helper to
make sure it works for different builds.

If we can avoid the involvement of libvirt, that would be better.

Thanks


>
>>> Also, libbpf dependency now exclusively for Linux.
>>> Libbpf is used for eBPF RSS steering, which is supported only by Linux TAP.
>>> There is no reason yet to build eBPF loader and helper for non Linux systems,
>>> even if libbpf is present.
>>>
>>> Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
>>> ---
>>>    ebpf/qemu-ebpf-rss-helper.c | 130 ++++++++++++++++++++++++++++++++++++
>>>    meson.build                 |  37 ++++++----
>>>    2 files changed, 154 insertions(+), 13 deletions(-)
>>>    create mode 100644 ebpf/qemu-ebpf-rss-helper.c
>>>
>>> diff --git a/ebpf/qemu-ebpf-rss-helper.c b/ebpf/qemu-ebpf-rss-helper.c
>>> new file mode 100644
>>> index 0000000000..fe68758f57
>>> --- /dev/null
>>> +++ b/ebpf/qemu-ebpf-rss-helper.c
>>> @@ -0,0 +1,130 @@
>>> +/*
>>> + * eBPF RSS Helper
>>> + *
>>> + * Developed by Daynix Computing LTD (http://www.daynix.com)
>>> + *
>>> + * Authors:
>>> + *  Andrew Melnychenko <andrew@daynix.com>
>>> + *
>>> + * This work is licensed under the terms of the GNU GPL, version 2.  See
>>> + * the COPYING file in the top-level directory.
>>> + *
>>> + * Description: This is helper program for libvirtd.
>>> + *              It loads eBPF RSS program and passes fds through unix socket.
>>> + *              Built by meson, target - 'qemu-ebpf-rss-helper'.
>>> + */
>>> +
>>> +#include <stdio.h>
>>> +#include <stdint.h>
>>> +#include <stdlib.h>
>>> +#include <stdbool.h>
>>> +#include <getopt.h>
>>> +#include <memory.h>
>>> +#include <errno.h>
>>> +#include <sys/socket.h>
>>> +
>>> +#include "ebpf_rss.h"
>>> +
>>> +#include "qemu-helper-stamp.h"
>>> +
>>> +void QEMU_HELPER_STAMP(void) {}
>>> +
>>> +static int send_fds(int socket, int *fds, int n)
>>> +{
>>> +    struct msghdr msg = {};
>>> +    struct cmsghdr *cmsg = NULL;
>>> +    char buf[CMSG_SPACE(n * sizeof(int))];
>>> +    char dummy_buffer = 0;
>>> +    struct iovec io = { .iov_base = &dummy_buffer,
>>> +                        .iov_len = sizeof(dummy_buffer) };
>>> +
>>> +    memset(buf, 0, sizeof(buf));
>>> +
>>> +    msg.msg_iov = &io;
>>> +    msg.msg_iovlen = 1;
>>> +    msg.msg_control = buf;
>>> +    msg.msg_controllen = sizeof(buf);
>>> +
>>> +    cmsg = CMSG_FIRSTHDR(&msg);
>>> +    cmsg->cmsg_level = SOL_SOCKET;
>>> +    cmsg->cmsg_type = SCM_RIGHTS;
>>> +    cmsg->cmsg_len = CMSG_LEN(n * sizeof(int));
>>> +
>>> +    memcpy(CMSG_DATA(cmsg), fds, n * sizeof(int));
>>> +
>>> +    return sendmsg(socket, &msg, 0);
>>> +}
>>> +
>>> +static void print_help_and_exit(const char *prog, int exitcode)
>>> +{
>>> +    fprintf(stderr, "%s - load eBPF RSS program for qemu and pass eBPF fds"
>>> +            " through unix socket.\n", prog);
>>> +    fprintf(stderr, "\t--fd <num>, -f <num> - unix socket file descriptor"
>>> +            " used to pass eBPF fds.\n");
>>> +    fprintf(stderr, "\t--help, -h - this help.\n");
>>> +    exit(exitcode);
>>> +}
>>> +
>>> +int main(int argc, char **argv)
>>> +{
>>> +    char *fd_string = NULL;
>>> +    int unix_fd = 0;
>>> +    struct EBPFRSSContext ctx = {};
>>> +    int fds[EBPF_RSS_MAX_FDS] = {};
>>> +    int ret = -1;
>>> +
>>> +    for (;;) {
>>> +        int c;
>>> +        static struct option long_options[] = {
>>> +                {"help",  no_argument, 0, 'h'},
>>> +                {"fd",  required_argument, 0, 'f'},
>>> +                {0, 0, 0, 0}
>>> +        };
>>> +        c = getopt_long(argc, argv, "hf:",
>>> +                long_options, NULL);
>>> +
>>> +        if (c == -1) {
>>> +            break;
>>> +        }
>>> +
>>> +        switch (c) {
>>> +        case 'f':
>>> +            fd_string = optarg;
>>> +            break;
>>> +        case 'h':
>>> +        default:
>>> +            print_help_and_exit(argv[0],
>>> +                    c == 'h' ? EXIT_SUCCESS : EXIT_FAILURE);
>>> +        }
>>> +    }
>>> +
>>> +    if (!fd_string) {
>>> +        fprintf(stderr, "Unix file descriptor not present.\n");
>>> +        print_help_and_exit(argv[0], EXIT_FAILURE);
>>> +    }
>>> +
>>> +    unix_fd = atoi(fd_string);
>>> +
>>> +    if (!unix_fd) {
>>> +        fprintf(stderr, "Unix file descriptor is invalid.\n");
>>> +        return EXIT_FAILURE;
>>> +    }
>>> +
>>> +    ebpf_rss_init(&ctx);
>>> +    if (!ebpf_rss_load(&ctx)) {
>>> +        fprintf(stderr, "Can't load ebpf.\n");
>>> +        return EXIT_FAILURE;
>>> +    }
>>> +    fds[0] = ctx.program_fd;
>>> +    fds[1] = ctx.map_configuration;
>>> +
>>> +    ret = send_fds(unix_fd, fds, EBPF_RSS_MAX_FDS);
>>> +    if (ret < 0) {
>>> +        fprintf(stderr, "Issue while sending fds: %s.\n", strerror(errno));
>>> +    }
>>> +
>>> +    ebpf_rss_unload(&ctx);
>>> +
>>> +    return ret < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
>>> +}
>>> +
>>> diff --git a/meson.build b/meson.build
>>> index 257e51d91b..913aa1fee5 100644
>>> --- a/meson.build
>>> +++ b/meson.build
>>> @@ -1033,19 +1033,22 @@ if not get_option('fuse_lseek').disabled()
>>>    endif
>>>
>>>    # libbpf
>>> -libbpf = dependency('libbpf', required: get_option('bpf'), method: 'pkg-config')
>>> -if libbpf.found() and not cc.links('''
>>> -   #include <bpf/libbpf.h>
>>> -   int main(void)
>>> -   {
>>> -     bpf_object__destroy_skeleton(NULL);
>>> -     return 0;
>>> -   }''', dependencies: libbpf)
>>> -  libbpf = not_found
>>> -  if get_option('bpf').enabled()
>>> -    error('libbpf skeleton test failed')
>>> -  else
>>> -    warning('libbpf skeleton test failed, disabling')
>>> +libbpf = not_found
>>> +if targetos == 'linux'
>>> +  libbpf = dependency('libbpf', required: get_option('bpf'), method: 'pkg-config')
>>> +  if libbpf.found() and not cc.links('''
>>> +    #include <bpf/libbpf.h>
>>> +    int main(void)
>>> +    {
>>> +      bpf_object__destroy_skeleton(NULL);
>>
>> Do we need to test whether the bpf can do mmap() here?
>>
>> Thanks
>>
>>
>>> +      return 0;
>>> +    }''', dependencies: libbpf)
>>> +    libbpf = not_found
>>> +    if get_option('bpf').enabled()
>>> +      error('libbpf skeleton test failed')
>>> +    else
>>> +      warning('libbpf skeleton test failed, disabling')
>>> +    endif
>>>      endif
>>>    endif
>>>
>>> @@ -2423,6 +2426,14 @@ if have_tools
>>>                   dependencies: [authz, crypto, io, qom, qemuutil,
>>>                                  libcap_ng, mpathpersist],
>>>                   install: true)
>>> +
>>> +    if libbpf.found()
>>> +        executable('qemu-ebpf-rss-helper', files(
>>> +                   'ebpf/qemu-ebpf-rss-helper.c', 'ebpf/ebpf_rss.c'),
>>> +                   dependencies: [qemuutil, libbpf, glib],
>>> +                   install: true,
>>> +                   install_dir: get_option('libexecdir'))
>>> +    endif
>>>      endif
>>>
>>>      if 'CONFIG_IVSHMEM' in config_host