xdp: add HW offload mode flag for installing programs

Add an installation-time flag for requesting that the program
be installed only if it can be offloaded to HW.

Internally new command for ndo_xdp is added, this way we avoid
putting checks into drivers since they all return -EINVAL on
an unknown command.
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -807,6 +807,7 @@ enum xdp_netdev_command {
 	 * when it is no longer used.
 	 */
 	XDP_SETUP_PROG,
+	XDP_SETUP_PROG_HW,
 	/* Check if a bpf program is set on the device.  The callee should
 	 * return true if a program is currently attached and running.
 	 */

include/uapi/linux/if_link.h

@@ -891,9 +891,12 @@ enum {
 #define XDP_FLAGS_UPDATE_IF_NOEXIST	(1U << 0)
 #define XDP_FLAGS_SKB_MODE		(1U << 1)
 #define XDP_FLAGS_DRV_MODE		(1U << 2)
+#define XDP_FLAGS_HW_MODE		(1U << 3)
+#define XDP_FLAGS_MODES			(XDP_FLAGS_SKB_MODE | \
+					 XDP_FLAGS_DRV_MODE | \
+					 XDP_FLAGS_HW_MODE)
 #define XDP_FLAGS_MASK			(XDP_FLAGS_UPDATE_IF_NOEXIST | \
-					 XDP_FLAGS_SKB_MODE | \
-					 XDP_FLAGS_DRV_MODE)
+					 XDP_FLAGS_MODES)
 
 /* These are stored into IFLA_XDP_ATTACHED on dump. */
 enum {

net/core/dev.c

@@ -6957,7 +6957,10 @@ static int dev_xdp_install(struct net_device *dev, xdp_op_t xdp_op,
 	struct netdev_xdp xdp;
 
 	memset(&xdp, 0, sizeof(xdp));
-	xdp.command = XDP_SETUP_PROG;
+	if (flags & XDP_FLAGS_HW_MODE)
+		xdp.command = XDP_SETUP_PROG_HW;
+	else
+		xdp.command = XDP_SETUP_PROG;
 	xdp.extack = extack;
 	xdp.flags = flags;
 	xdp.prog = prog;
@@ -6985,7 +6988,7 @@ int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
 	ASSERT_RTNL();
 
 	xdp_op = xdp_chk = ops->ndo_xdp;
-	if (!xdp_op && (flags & XDP_FLAGS_DRV_MODE))
+	if (!xdp_op && (flags & (XDP_FLAGS_DRV_MODE | XDP_FLAGS_HW_MODE)))
 		return -EOPNOTSUPP;
 	if (!xdp_op || (flags & XDP_FLAGS_SKB_MODE))
 		xdp_op = generic_xdp_install;

net/core/rtnetlink.c

@@ -16,6 +16,7 @@
  *	Vitaly E. Lavrov		RTA_OK arithmetics was wrong.
  */
 
+#include <linux/bitops.h>
 #include <linux/errno.h>
 #include <linux/module.h>
 #include <linux/types.h>
@@ -2253,8 +2254,7 @@ 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)) {
+			if (hweight32(xdp_flags & XDP_FLAGS_MODES) > 1) {
 				err = -EINVAL;
 				goto errout;
 			}