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Date: Wed, 7 Nov 2018 15:37:07 -0800
From: Shannon Nelson <shannon.lee.nelson@...il.com>
To: daniel@...earbox.net
Cc: john.fastabend@...il.com,
Shannon Nelson <shannon.nelson@...cle.com>, ast@...nel.org,
netdev@...r.kernel.org, eric.dumazet@...il.com,
silviu.smarandache@...cle.com
Subject: Re: [PATCH bpf-next] xdp: sample code for redirecting vlan packets to
specific cpus
On Wed, Nov 7, 2018 at 1:44 PM Daniel Borkmann <daniel@...earbox.net> wrote:
>
> On 10/29/2018 11:11 PM, John Fastabend wrote:
> > On 10/29/2018 02:19 PM, Shannon Nelson wrote:
> >> This is an example of using XDP to redirect the processing of
> >> particular vlan packets to specific CPUs. This is in response
> >> to comments received on a kernel patch put forth previously
> >> to do something similar using RPS.
> >> https://www.spinics.net/lists/netdev/msg528210.html
> >> [PATCH net-next] net: enable RPS on vlan devices
> >>
> >> This XDP application watches for inbound vlan-tagged packets
> >> and redirects those packets to be processed on a specific CPU
> >> as configured in a BPF map. The BPF map can be modified by
> >> this user program, which can also load and unload the kernel
> >> XDP code.
> >>
> >> One example use is for supporting VMs where we can't control the
> >> OS being used: we'd like to separate the VM CPU processing from
> >> the host's CPUs as a way to help mitigate L1TF related issues.
> >> When running the VM's traffic on a vlan we can stick the host's
> >> Rx processing on one set of CPUs separate from the VM's CPUs.
> >>
> >> This example currently uses a vlan key and cpu value in the
> >> BPF map, so only can do one CPU per vlan. This could easily
> >> be modified to use a bitpattern of CPUs rather than a CPU id
> >> to allow multiple CPUs per vlan.
> >
> > Great, so does this solve your use case then? At least on drivers
> > with XDP support?
> >
> >>
> >> Signed-off-by: Shannon Nelson <shannon.nelson@...cle.com>
> >> ---
> >
> > Some really small and trivial nits below.
> >
> > Acked-by: John Fastabend <john.fastabend@...il.com>
> >
> > [...]
> >
> >> + if (install) {
> >> +
> >
> > new line probably not needed.
> >
> >> + /* check to see if already installed */
> >> + errno = 0;
> >> + access(pin_prog_name, R_OK);
> >> + if (errno != ENOENT) {
> >> + fprintf(stderr, "ERR: %s is already installed\n", argv[0]);
> >> + return -1;
> >> + }
> >> +
> >> + /* load the XDP program and maps with the convenient library */
> >> + if (load_bpf_file(filename)) {
> >> + fprintf(stderr, "ERR: load_bpf_file(%s): \n%s",
> >> + filename, bpf_log_buf);
> >> + return -1;
> >> + }
> >> + if (!prog_fd[0]) {
> >> + fprintf(stderr, "ERR: load_bpf_file(%s): %d %s\n",
> >> + filename, errno, strerror(errno));
> >> + return -1;
> >> + }
> >> +
> >> + /* pin the XDP program and maps */
> >> + if (bpf_obj_pin(prog_fd[0], pin_prog_name) < 0) {
> >> + fprintf(stderr, "ERR: bpf_obj_pin(%s): %d %s\n",
> >> + pin_prog_name, errno, strerror(errno));
> >> + if (errno == 2)
> >> + fprintf(stderr, " (is the BPF fs mounted on /sys/fs/bpf?)\n");
> >> + return -1;
> >> + }
> >> + if (bpf_obj_pin(map_fd[0], pin_vlanmap_name) < 0) {
> >> + fprintf(stderr, "ERR: bpf_obj_pin(%s): %d %s\n",
> >> + pin_vlanmap_name, errno, strerror(errno));
> >> + return -1;
> >> + }
> >> + if (bpf_obj_pin(map_fd[2], pin_countermap_name) < 0) {
> >> + fprintf(stderr, "ERR: bpf_obj_pin(%s): %d %s\n",
> >> + pin_countermap_name, errno, strerror(errno));
> >> + return -1;
> >> + }
> >> +
> >> + /* prep the vlan map with "not used" values */
> >> + c64 = UNDEF_CPU;
> >> + for (v64 = 0; v64 < 4096; v64++) {
> >
> > maybe #define MAX_VLANS 4096 just to avoid constants.
> >
> >> + if (bpf_map_update_elem(map_fd[0], &v64, &c64, 0)) {
> >> + fprintf(stderr, "ERR: preping vlan map failed on v=%llu: %d %s\n",
> >> + v64, errno, strerror(errno));
> >> + return -1;
> >> + }
> >> + }
> >> +
> >> + /* prep the cpumap with queue sizes */
> >> + c64 = 128+64; /* see note in xdp_redirect_cpu_user.c */
> >> + for (v64 = 0; v64 < MAX_CPUS; v64++) {
> >> + if (bpf_map_update_elem(map_fd[1], &v64, &c64, 0)) {
> >> + if (errno == ENODEV) {
> >> + /* Save the last CPU number attempted
> >> + * into the counters map
> >> + */
> >> + c64 = CPU_COUNT;
> >> + ret = bpf_map_update_elem(map_fd[2], &c64, &v64, 0);
> >> + break;
> >> + }
> >> +
> >> + fprintf(stderr, "ERR: preping cpu map failed on v=%llu: %d %s\n",
> >> + v64, errno, strerror(errno));
> >> + return -1;
> >> + }
> >> + }
> >> +
> >> + /* wire the XDP program to the device */
> >> + if (bpf_set_link_xdp_fd(ifindex, prog_fd[0], 0) < 0) {
> >> + fprintf(stderr, "ERR: bpf_set_link_xdp_fd(): %d %s\n",
> >> + errno, strerror(errno));
> >> + return -1;
> >> + }
> >> +
> >> + return 0;
> >> + }
> >> +
> >> + if (remove) {
> >> +
>
> Ditto
>
> >> + /* unlink the program from the device */
> >> + if (bpf_set_link_xdp_fd(ifindex, -1, 0) < 0)
> >> + fprintf(stderr, "ERR: bpf_set_link_xdp_fd(): %d %s\n",
> >> + errno, strerror(errno));
> >> +
> >> + /* unlink pinned files */
> >> + if (unlink(pin_prog_name))
> >> + fprintf(stderr, "ERR: unlink(%s): %d %s\n",
> >> + pin_prog_name, errno, strerror(errno));
> >> + if (unlink(pin_vlanmap_name))
> >> + fprintf(stderr, "ERR: unlink(%s): %d %s\n",
> >> + pin_vlanmap_name, errno, strerror(errno));
> >> + if (unlink(pin_countermap_name))
> >> + fprintf(stderr, "ERR: unlink(%s): %d %s\n",
> >> + pin_countermap_name, errno, strerror(errno));
> >> +
> >> + return 0;
> >> + }
> >> +
> >> + if (vlan == 0) {
> >> + fprintf(stderr, "ERR: required option --vlan missing\n");
> >> + goto error;
> >> + }
> >> +
> >> + if (cpu == MAX_CPUS && vlan > 0) {
> >> + fprintf(stderr, "ERR: required option --cpu missing\n");
> >> + goto error;
> >> + }
> >> +
> >> + vfd = bpf_obj_get(pin_vlanmap_name);
> >> + if (vfd < 0) {
> >> + fprintf(stderr, "ERR: can't find pinned map %s: %d %s\n",
> >> + pin_vlanmap_name, errno, strerror(errno));
> >> + if (errno == ENOENT)
> >> + fprintf(stderr, " (has %s been installed yet?)\n", argv[0]);
> >> + return -1;
> >> + }
> >> +
> >> + /* decode the requested action */
> >> + if (vlan > 0) {
> >> + /* check cpu against the max value found */
> >> + cfd = bpf_obj_get(pin_countermap_name);
> >> + if (cfd < 0) {
> >> + fprintf(stderr, "ERR: can't find pinned map %s: %d %s\n",
> >> + pin_countermap_name, errno, strerror(errno));
> >> + return -1;
> >> + }
> >> + c64 = CPU_COUNT;
> >> + ret = bpf_map_lookup_elem(cfd, &c64, &v64);
> >> + if (cpu >= v64) {
> >
> > Need to check ret code?
>
> Yeah, I expect this would have another respin, thanks!
Being as I no longer work for Oracle (as of this week), and I'm deep
into the spin-up of learning a new company, this won't be happening
right away. Let's consider this an RFC, and I will try to follow up
in the "near" future.
Thanks
sln
>
> >> + fprintf(stderr, "ERR: cpu %d greater than max %llu\n", cpu, v64);
> >> + return -1;
> >> + }
> >> +
> >> + /* Note that the value and key pointers really do need to be
> >> + * pointers to 64-bit values, else things get a bit muddled.
> >> + */
> >> + v64 = vlan;
> >> + c64 = cpu;
> >> + ret = bpf_map_update_elem(vfd, &v64, &c64, 0);
> >> + if (ret) {
> >> + fprintf(stderr, "Adding vlan %d CPU %d failed: %d %s\n",
> >> + vlan, cpu, errno, strerror(errno));
> >> + return -1;
> >> + }
> >> +
> >> + } else {
> >> + v64 = -vlan;
> >> + c64 = UNDEF_CPU;
> >> +
> >> + /* We can't actually delete from a TYPE_ARRAY map, so we
> >> + * simply set it to an undefined value.
> >> + */
> >> + ret = bpf_map_update_elem(vfd, &v64, &c64, 0);
> >> + if (ret) {
> >> + fprintf(stderr, "Delete of vlan %llu failed: %d %s\n",
> >> + v64, errno, strerror(errno));
> >> + return -1;
> >> + }
> >> + }
> >> +
> >> + return 0;
> >> +
> >> +error:
> >> + usage(argv);
> >> + return -1;
> >> +}
> >>
> >
>
--
==============================================
Mr. Shannon Nelson Parents can't afford to be squeamish.
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