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

[Jason Wang]

On Thu, Sep 9, 2021 at 8:00 AM Yuri Benditovich
<yuri.benditovich@daynix.com> wrote:
>
> On Wed, Sep 8, 2021 at 6:45 AM Jason Wang <jasowang@redhat.com> wrote:
> >
> > On Tue, Sep 7, 2021 at 6:40 PM Yuri Benditovich
> > <yuri.benditovich@daynix.com> wrote:
> > >
> > > 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.
> > >
> > > Hi Jason,
> > >
> > > Indeed I did not get the idea, can you please explain it in more
> > > details (as detailed as possible to avoid future misunderstanding),
> > > especially how exactly we can use the set-uid and what is the 'default' 
> > > helper.
> > > We also would prefer to do everything from qemu but we do not see how
> > > we can do that.
> >
> >
> Some more questions to understand the idea better:
> > Something like:
> >
> > 1) -netdev tap,rss_helper=/path/to/name
>
> So, on each editing of 'emulator' in the xml  the helper path should
> be set manually or be default?

It could done manually, or we can have a default path.

>
> > 2) having a sample/default helper implemented in Qemu
>
> Does it mean the default helper is the code in the qemu (without
> running additional executable, like it does today)

Yes.

 or this is qemu
> itself with dedicated command line?
> As far as I remember Daniel had strong objections of ever running qemu
> with capabilities

Qemu won't run with capabilities but the helper.

>
> > 3) we can introduce something special path like "default", then if
> > -netdev tap,rss_helper="default" is specified, qemu will use the
> > sample helper
>
> Probably this is not so important but the rss helper and rss in
> general has no relation to netdev, much more they are related to
> virtio-net

So I think the reason for this is that we currently only support
eBPF/RSS for tap.

>
> >
> > So we have:
> > 1) set set-uid for the helper
> Who and when does set-uid to the helper binary? Only installer or
> libvirt can do that, correct?

Yes, it could be done the installer, or other system provision tools.

>
> > 2) libvirt may just choose to launch the default helper
> All this discussion is to avoid launching the helper from libvirt, correct?

Sorry, it's a typo. I meant, libvirt launch qemu, and then qemu will
launch the helper.

Thanks

>
> >
> > >
> > > Our main points (what should be addressed):
> > > - qemu should be able to load ebpf and use the maps when it runs from
> > > libvirt (without special caps) and standalone (with caps)
> >
> > This is solved by leaving the privileged operations to the helper with 
> > set-uid.
> >
> > > - it is possible that there are different qemu builds on the machine,
> > > one of them might be installed, their ebpf's might be different and
> > > the interface between qemu and ebpf (exact content of maps and number
> > > of maps)
> >
> > We can use different helpers in this way.
> >
> > > - qemu configures the RSS dynamically according to the commands
> > > provided by the guest
> >
> > Consider we decided to use mmap() based maps, this is not an issue.
> >
> > Or am I missing something?
> >
> > Thanks
> >
> > >
> > > Thanks in advance
> > > Yuri
> > >
> > > >
> > > > 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
> > > >
> > >
> >
>