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Date: Mon, 29 Oct 2018 15:11:01 -0700
From: John Fastabend <john.fastabend@...il.com>
To: Shannon Nelson <shannon.nelson@...cle.com>, ast@...nel.org,
daniel@...earbox.net
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com,
silviu.smarandache@...cle.com, shannon.lee.nelson@...il.com
Subject: Re: [PATCH bpf-next] xdp: sample code for redirecting vlan packets to
specific cpus
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) {
> +
> + /* 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?
> + 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;
> +}
>
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