xdp: add flag to enforce driver mode

After commit b5cdae3291f7 ("net: Generic XDP") we automatically fall
back to a generic XDP variant if the driver does not support native
XDP. Allow for an option where the user can specify that always the
native XDP variant should be selected and in case it's not supported
by a driver, just bail out.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 23 insertions, 5 deletions

diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index 8e56ac70e0d1..549ac8a98b44 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -888,9 +888,11 @@ enum {
 /* XDP section */
 
 #define XDP_FLAGS_UPDATE_IF_NOEXIST     (1U << 0)
-#define XDP_FLAGS_SKB_MODE              (2U << 0)
+#define XDP_FLAGS_SKB_MODE              (1U << 1)
+#define XDP_FLAGS_DRV_MODE              (1U << 2)
 #define XDP_FLAGS_MASK                  (XDP_FLAGS_UPDATE_IF_NOEXIST | \
-                                         XDP_FLAGS_SKB_MODE)
+                                         XDP_FLAGS_SKB_MODE | \
+                                         XDP_FLAGS_DRV_MODE)
 
 enum {
         IFLA_XDP_UNSPEC,
diff --git a/net/core/dev.c b/net/core/dev.c
index 96cf83da0d66..e56cb71351d4 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6873,6 +6873,8 @@ int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
         ASSERT_RTNL();
 
         xdp_op = ops->ndo_xdp;
+        if (!xdp_op && (flags & XDP_FLAGS_DRV_MODE))
+                return -EOPNOTSUPP;
         if (!xdp_op || (flags & XDP_FLAGS_SKB_MODE))
                 xdp_op = generic_xdp_install;
 
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index bcb0f610ee42..dda9f1636356 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -2199,6 +2199,11 @@ static int do_setlink(const struct sk_buff *skb,
                                 err = -EINVAL;
                                 goto errout;
                         }
+                        if ((xdp_flags & XDP_FLAGS_SKB_MODE) &&
+                            (xdp_flags & XDP_FLAGS_DRV_MODE)) {
+                                err = -EINVAL;
+                                goto errout;
+                        }
                 }
 
                 if (xdp[IFLA_XDP_FD]) {
diff --git a/samples/bpf/xdp1_user.c b/samples/bpf/xdp1_user.c
index 378850c70eb8..17be9ea3ecb2 100644
--- a/samples/bpf/xdp1_user.c
+++ b/samples/bpf/xdp1_user.c
@@ -62,13 +62,14 @@ static void usage(const char *prog)
         fprintf(stderr,
                 "usage: %s [OPTS] IFINDEX\n\n"
                 "OPTS:\n"
-                "    -S    use skb-mode\n",
+                "    -S    use skb-mode\n"
+                "    -N    enforce native mode\n",
                 prog);
 }
 
 int main(int argc, char **argv)
 {
-        const char *optstr = "S";
+        const char *optstr = "SN";
         char filename[256];
         int opt;
 
@@ -77,6 +78,9 @@ int main(int argc, char **argv)
                 case 'S':
                         xdp_flags |= XDP_FLAGS_SKB_MODE;
                         break;
+                case 'N':
+                        xdp_flags |= XDP_FLAGS_DRV_MODE;
+                        break;
                 default:
                         usage(basename(argv[0]));
                         return 1;
diff --git a/samples/bpf/xdp_tx_iptunnel_user.c b/samples/bpf/xdp_tx_iptunnel_user.c
index 92b8bde9337c..631cdcc41c97 100644
--- a/samples/bpf/xdp_tx_iptunnel_user.c
+++ b/samples/bpf/xdp_tx_iptunnel_user.c
@@ -79,6 +79,8 @@ static void usage(const char *cmd)
         printf("    -m <dest-MAC> Used in sending the IP Tunneled pkt\n");
         printf("    -T <stop-after-X-seconds> Default: 0 (forever)\n");
         printf("    -P <IP-Protocol> Default is TCP\n");
+        printf("    -S use skb-mode\n");
+        printf("    -N enforce native mode\n");
         printf("    -h Display this help\n");
 }
 
@@ -138,7 +140,7 @@ int main(int argc, char **argv)
 {
         unsigned char opt_flags[256] = {};
         unsigned int kill_after_s = 0;
-        const char *optstr = "i:a:p:s:d:m:T:P:Sh";
+        const char *optstr = "i:a:p:s:d:m:T:P:SNh";
         int min_port = 0, max_port = 0;
         struct iptnl_info tnl = {};
         struct rlimit r = {RLIM_INFINITY, RLIM_INFINITY};
@@ -206,6 +208,9 @@ int main(int argc, char **argv)
                 case 'S':
                         xdp_flags |= XDP_FLAGS_SKB_MODE;
                         break;
+                case 'N':
+                        xdp_flags |= XDP_FLAGS_DRV_MODE;
+                        break;
                 default:
                         usage(argv[0]);
                         return 1;