On Mon, Mar 29, 2021 at 01:05:44PM +0200, Toke Høiland-Jørgensen wrote:
> Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx> writes:
>
> > Currently, if there are multiple xdpsock instances running on a single
> > interface and in case one of the instances is terminated, the rest of
> > them are left in an inoperable state due to the fact of unloaded XDP
> > prog from interface.
> >
> > Consider the scenario below:
> >
> > // load xdp prog and xskmap and add entry to xskmap at idx 10
> > $ sudo ./xdpsock -i ens801f0 -t -q 10
> >
> > // add entry to xskmap at idx 11
> > $ sudo ./xdpsock -i ens801f0 -t -q 11
> >
> > terminate one of the processes and another one is unable to work due to
> > the fact that the XDP prog was unloaded from interface.
> >
> > To address that, step away from setting bpf prog in favour of bpf_link.
> > This means that refcounting of BPF resources will be done automatically
> > by bpf_link itself.
> >
> > Provide backward compatibility by checking if underlying system is
> > bpf_link capable. Do this by looking up/creating bpf_link on loopback
> > device. If it failed in any way, stick with netlink-based XDP prog.
> > therwise, use bpf_link-based logic.
> >
> > When setting up BPF resources during xsk socket creation, check whether
> > bpf_link for a given ifindex already exists via set of calls to
> > bpf_link_get_next_id -> bpf_link_get_fd_by_id -> bpf_obj_get_info_by_fd
> > and comparing the ifindexes from bpf_link and xsk socket.
> >
> > For case where resources exist but they are not AF_XDP related, bail out
> > and ask user to remove existing prog and then retry.
> >
> > Lastly, do a bit of refactoring within __xsk_setup_xdp_prog and pull out
> > existing code branches based on prog_id value onto separate functions
> > that are responsible for resource initialization if prog_id was 0 and
> > for lookup existing resources for non-zero prog_id as that implies that
> > XDP program is present on the underlying net device. This in turn makes
> > it easier to follow, especially the teardown part of both branches.
> >
> > Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx>
>
> The logic is much improved in this version! A few smallish issues below:
Glad to hear that!
>
> > ---
> > tools/lib/bpf/xsk.c | 259 ++++++++++++++++++++++++++++++++++++--------
> > 1 file changed, 214 insertions(+), 45 deletions(-)
> >
> > diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
> > index 526fc35c0b23..c75067f0035f 100644
> > --- a/tools/lib/bpf/xsk.c
> > +++ b/tools/lib/bpf/xsk.c
> > @@ -28,6 +28,7 @@
> > #include <sys/mman.h>
> > #include <sys/socket.h>
> > #include <sys/types.h>
> > +#include <linux/if_link.h>
> >
> > #include "bpf.h"
> > #include "libbpf.h"
> > @@ -70,8 +71,10 @@ struct xsk_ctx {
> > int ifindex;
> > struct list_head list;
> > int prog_fd;
> > + int link_fd;
> > int xsks_map_fd;
> > char ifname[IFNAMSIZ];
> > + bool has_bpf_link;
> > };
> >
> > struct xsk_socket {
> > @@ -409,7 +412,7 @@ static int xsk_load_xdp_prog(struct xsk_socket *xsk)
> > static const int log_buf_size = 16 * 1024;
> > struct xsk_ctx *ctx = xsk->ctx;
> > char log_buf[log_buf_size];
> > - int err, prog_fd;
> > + int prog_fd;
> >
> > /* This is the fallback C-program:
> > * SEC("xdp_sock") int xdp_sock_prog(struct xdp_md *ctx)
> > @@ -499,14 +502,43 @@ static int xsk_load_xdp_prog(struct xsk_socket *xsk)
> > return prog_fd;
> > }
> >
> > - err = bpf_set_link_xdp_fd(xsk->ctx->ifindex, prog_fd,
> > - xsk->config.xdp_flags);
> > + ctx->prog_fd = prog_fd;
> > + return 0;
> > +}
> > +
> > +static int xsk_create_bpf_link(struct xsk_socket *xsk)
> > +{
> > + /* bpf_link only accepts XDP_FLAGS_MODES, but xsk->config.xdp_flags
> > + * might have set XDP_FLAGS_UPDATE_IF_NOEXIST
> > + */
> > + DECLARE_LIBBPF_OPTS(bpf_link_create_opts, opts,
> > + .flags = (xsk->config.xdp_flags & XDP_FLAGS_MODES));
>
> This will silently suppress any new flags as well; that's not a good
> idea. Rather mask out the particular flag (UPDATE_IF_NOEXIST) and pass
> everything else through so the kernel can reject invalid ones.
I'd say it's fine as it matches the check:
/* link supports only XDP mode flags */
if (link && (flags & ~XDP_FLAGS_MODES)) {
NL_SET_ERR_MSG(extack, "Invalid XDP flags for BPF link attachment");
return -EINVAL;
}
from dev_xdp_attach() in net/core/dev.c ?
>
> > + struct xsk_ctx *ctx = xsk->ctx;
> > + __u32 prog_id = 0;
> > + int link_fd;
> > + int err;
> > +
> > + err = bpf_get_link_xdp_id(ctx->ifindex, &prog_id, xsk->config.xdp_flags);
> > if (err) {
> > - close(prog_fd);
> > + pr_warn("getting XDP prog id failed\n");
> > return err;
> > }
> >
> > - ctx->prog_fd = prog_fd;
> > + /* if there's a netlink-based XDP prog loaded on interface, bail out
> > + * and ask user to do the removal by himself
> > + */
> > + if (prog_id) {
> > + pr_warn("Netlink-based XDP prog detected, please unload it in order to launch AF_XDP prog\n");
> > + return -EINVAL;
> > + }
> > +
> > + link_fd = bpf_link_create(ctx->prog_fd, ctx->ifindex, BPF_XDP, &opts);
> > + if (link_fd < 0) {
> > + pr_warn("bpf_link_create failed: %s\n", strerror(errno));
> > + return link_fd;
> > + }
> > +
> > + ctx->link_fd = link_fd;
> > return 0;
> > }
> >
> > @@ -625,7 +657,6 @@ static int xsk_lookup_bpf_maps(struct xsk_socket *xsk)
> > close(fd);
> > }
> >
> > - err = 0;
> > if (ctx->xsks_map_fd == -1)
> > err = -ENOENT;
> >
> > @@ -642,6 +673,97 @@ static int xsk_set_bpf_maps(struct xsk_socket *xsk)
> > &xsk->fd, 0);
> > }
> >
> > +static int xsk_link_lookup(int ifindex, __u32 *prog_id, int *link_fd)
> > +{
> > + struct bpf_link_info link_info;
> > + __u32 link_len;
> > + __u32 id = 0;
> > + int err;
> > + int fd;
> > +
> > + while (true) {
> > + err = bpf_link_get_next_id(id, &id);
> > + if (err) {
> > + if (errno == ENOENT) {
> > + err = 0;
> > + break;
> > + }
> > + pr_warn("can't get next link: %s\n", strerror(errno));
> > + break;
> > + }
> > +
> > + fd = bpf_link_get_fd_by_id(id);
> > + if (fd < 0) {
> > + if (errno == ENOENT)
> > + continue;
> > + pr_warn("can't get link by id (%u): %s\n", id, strerror(errno));
> > + err = -errno;
> > + break;
> > + }
> > +
> > + link_len = sizeof(struct bpf_link_info);
> > + memset(&link_info, 0, link_len);
> > + err = bpf_obj_get_info_by_fd(fd, &link_info, &link_len);
> > + if (err) {
> > + pr_warn("can't get link info: %s\n", strerror(errno));
> > + close(fd);
> > + break;
> > + }
> > + if (link_info.type == BPF_LINK_TYPE_XDP) {
> > + if (link_info.xdp.ifindex == ifindex) {
> > + *link_fd = fd;
> > + if (prog_id)
> > + *prog_id = link_info.prog_id;
> > + break;
> > + }
> > + }
> > + close(fd);
> > + }
> > +
> > + return err;
> > +}
> > +
> > +static bool xsk_probe_bpf_link(void)
> > +{
> > + DECLARE_LIBBPF_OPTS(bpf_link_create_opts, opts,
> > + .flags = XDP_FLAGS_SKB_MODE);
> > + struct bpf_load_program_attr prog_attr;
> > + struct bpf_insn insns[2] = {
> > + BPF_MOV64_IMM(BPF_REG_0, XDP_PASS),
> > + BPF_EXIT_INSN()
> > + };
> > + int prog_fd, link_fd = -1;
> > + int ifindex_lo = 1;
> > + bool ret = false;
> > + int err;
> > +
> > + err = xsk_link_lookup(ifindex_lo, NULL, &link_fd);
> > + if (err)
> > + return ret;
> > +
> > + if (link_fd >= 0)
> > + return true;
> > +
> > + memset(&prog_attr, 0, sizeof(prog_attr));
> > + prog_attr.prog_type = BPF_PROG_TYPE_XDP;
> > + prog_attr.insns = insns;
> > + prog_attr.insns_cnt = ARRAY_SIZE(insns);
> > + prog_attr.license = "GPL";
> > +
> > + prog_fd = bpf_load_program_xattr(&prog_attr, NULL, 0);
> > + if (prog_fd < 0)
> > + return ret;
> > +
> > + link_fd = bpf_link_create(prog_fd, ifindex_lo, BPF_XDP, &opts);
> > + if (link_fd >= 0)
> > + ret = true;
> > +
> > + close(prog_fd);
> > + close(link_fd);
>
> This potentially calls close() on an invalid link_fd...
Will fix.
>
> > +
> > + return ret;
> > +}
> > +
> > static int xsk_create_xsk_struct(int ifindex, struct xsk_socket *xsk)
> > {
> > char ifname[IFNAMSIZ];
> > @@ -663,64 +785,108 @@ static int xsk_create_xsk_struct(int ifindex, struct xsk_socket *xsk)
> > ctx->ifname[IFNAMSIZ - 1] = 0;
> >
> > xsk->ctx = ctx;
> > + xsk->ctx->has_bpf_link = xsk_probe_bpf_link();
> >
> > return 0;
> > }
> >
> > -static int __xsk_setup_xdp_prog(struct xsk_socket *_xdp,
> > - int *xsks_map_fd)
> > +static int xsk_init_xdp_res(struct xsk_socket *xsk,
> > + int *xsks_map_fd)
> > {
> > - struct xsk_socket *xsk = _xdp;
> > struct xsk_ctx *ctx = xsk->ctx;
> > - __u32 prog_id = 0;
> > int err;
> >
> > - err = bpf_get_link_xdp_id(ctx->ifindex, &prog_id,
> > - xsk->config.xdp_flags);
> > + err = xsk_create_bpf_maps(xsk);
> > if (err)
> > return err;
> >
> > - if (!prog_id) {
> > - err = xsk_create_bpf_maps(xsk);
> > - if (err)
> > - return err;
> > + err = xsk_load_xdp_prog(xsk);
> > + if (err)
> > + goto err_load_xdp_prog;
> >
> > - err = xsk_load_xdp_prog(xsk);
> > - if (err) {
> > - goto err_load_xdp_prog;
> > - }
> > - } else {
> > - ctx->prog_fd = bpf_prog_get_fd_by_id(prog_id);
> > - if (ctx->prog_fd < 0)
> > - return -errno;
> > - err = xsk_lookup_bpf_maps(xsk);
> > - if (err) {
> > - close(ctx->prog_fd);
> > - return err;
> > - }
> > - }
> > + if (ctx->has_bpf_link)
> > + err = xsk_create_bpf_link(xsk);
> > + else
> > + err = bpf_set_link_xdp_fd(xsk->ctx->ifindex, ctx->prog_fd,
> > + xsk->config.xdp_flags);
> >
> > - if (xsk->rx) {
> > - err = xsk_set_bpf_maps(xsk);
> > - if (err) {
> > - if (!prog_id) {
> > - goto err_set_bpf_maps;
> > - } else {
> > - close(ctx->prog_fd);
> > - return err;
> > - }
> > - }
> > - }
> > - if (xsks_map_fd)
> > - *xsks_map_fd = ctx->xsks_map_fd;
> > + if (err)
> > + goto err_atach_xdp_prog;
>
> s/atach/attach/
Whoops :)
>
> -Toke
>
