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Date:   Sun, 12 Jul 2020 22:12:24 -0700
From:   Andrii Nakryiko <andriin@...com>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>, <ast@...com>,
        <daniel@...earbox.net>
CC:     <andrii.nakryiko@...il.com>, <kernel-team@...com>,
        Andrii Nakryiko <andriin@...com>, Andrey Ignatov <rdna@...com>,
        Takshak Chahande <ctakshak@...com>
Subject: [PATCH bpf-next 1/7] bpf, xdp: maintain info on attached XDP BPF programs in net_device

Instead of delegating to drivers, maintain information about which BPF
programs are attached in which XDP modes (generic/skb, driver, or hardware)
locally in net_device. This effectively obsoletes XDP_QUERY_PROG command.

Such re-organization simplifies existing code already. But it also allows to
further add bpf_link-based XDP attachments without drivers having to know
about any of this at all, which seems like a good setup.
XDP_SETUP_PROG/XDP_SETUP_PROG_HW are just low-level commands to driver to
install/uninstall active BPF program. All the higher-level concerns about
prog/link interaction will be contained within generic driver-agnostic logic.

All the XDP_QUERY_PROG calls to driver in dev_xdp_uninstall() were removed.
It's not clear for me why dev_xdp_uninstall() were passing previous prog_flags
when resetting installed programs. That seems unnecessary, plus most drivers
don't populate prog_flags anyways. Having XDP_SETUP_PROG vs XDP_SETUP_PROG_HW
should be enough of an indicator of what is required of driver to correctly
reset active BPF program.

Signed-off-by: Andrii Nakryiko <andriin@...com>
---
 include/linux/netdevice.h |  17 +++++-
 net/core/dev.c            | 113 +++++++++++++++++++-------------------
 net/core/rtnetlink.c      |   5 +-
 3 files changed, 73 insertions(+), 62 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 39e28e11863c..d5630e535836 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -887,6 +887,17 @@ struct netlink_ext_ack;
 struct xdp_umem;
 struct xdp_dev_bulk_queue;
 
+enum bpf_xdp_mode {
+	XDP_MODE_SKB = 0,
+	XDP_MODE_DRV = 1,
+	XDP_MODE_HW = 2,
+	__MAX_XDP_MODE
+};
+
+struct bpf_xdp_entity {
+	struct bpf_prog *prog;
+};
+
 struct netdev_bpf {
 	enum bpf_netdev_command command;
 	union {
@@ -2134,6 +2145,9 @@ struct net_device {
 	/* MACsec management functions */
 	const struct macsec_ops *macsec_ops;
 #endif
+
+	/* protected by rtnl_lock */
+	struct bpf_xdp_entity	xdp_state[__MAX_XDP_MODE];
 };
 #define to_net_dev(d) container_of(d, struct net_device, dev)
 
@@ -3809,8 +3823,7 @@ struct sk_buff *dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
 typedef int (*bpf_op_t)(struct net_device *dev, struct netdev_bpf *bpf);
 int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
 		      int fd, int expected_fd, u32 flags);
-u32 __dev_xdp_query(struct net_device *dev, bpf_op_t xdp_op,
-		    enum bpf_netdev_command cmd);
+u32 dev_xdp_prog_id(struct net_device *dev, enum bpf_xdp_mode mode);
 int xdp_umem_query(struct net_device *dev, u16 queue_id);
 
 int __dev_forward_skb(struct net_device *dev, struct sk_buff *skb);
diff --git a/net/core/dev.c b/net/core/dev.c
index c02bae927812..d3b82b664e2d 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8713,84 +8713,82 @@ int dev_change_proto_down_generic(struct net_device *dev, bool proto_down)
 }
 EXPORT_SYMBOL(dev_change_proto_down_generic);
 
-u32 __dev_xdp_query(struct net_device *dev, bpf_op_t bpf_op,
-		    enum bpf_netdev_command cmd)
+static struct bpf_prog *dev_xdp_prog(struct net_device *dev, enum bpf_xdp_mode mode)
 {
-	struct netdev_bpf xdp;
-
-	if (!bpf_op)
-		return 0;
+	return dev->xdp_state[mode].prog;
+}
 
-	memset(&xdp, 0, sizeof(xdp));
-	xdp.command = cmd;
+u32 dev_xdp_prog_id(struct net_device *dev, enum bpf_xdp_mode mode)
+{
+	struct bpf_prog *prog = dev_xdp_prog(dev, mode);
 
-	/* Query must always succeed. */
-	WARN_ON(bpf_op(dev, &xdp) < 0 && cmd == XDP_QUERY_PROG);
+	return prog ? prog->aux->id : 0;
+}
 
-	return xdp.prog_id;
+static void dev_xdp_set_prog(struct net_device *dev, enum bpf_xdp_mode mode,
+			     struct bpf_prog *prog)
+{
+	dev->xdp_state[mode].prog = prog;
 }
 
-static int dev_xdp_install(struct net_device *dev, bpf_op_t bpf_op,
-			   struct netlink_ext_ack *extack, u32 flags,
-			   struct bpf_prog *prog)
+static int dev_xdp_install(struct net_device *dev, enum bpf_xdp_mode mode,
+			   bpf_op_t bpf_op, struct netlink_ext_ack *extack,
+			   u32 flags, struct bpf_prog *prog)
 {
-	bool non_hw = !(flags & XDP_FLAGS_HW_MODE);
-	struct bpf_prog *prev_prog = NULL;
 	struct netdev_bpf xdp;
 	int err;
 
-	if (non_hw) {
-		prev_prog = bpf_prog_by_id(__dev_xdp_query(dev, bpf_op,
-							   XDP_QUERY_PROG));
-		if (IS_ERR(prev_prog))
-			prev_prog = NULL;
-	}
-
 	memset(&xdp, 0, sizeof(xdp));
-	if (flags & XDP_FLAGS_HW_MODE)
-		xdp.command = XDP_SETUP_PROG_HW;
-	else
-		xdp.command = XDP_SETUP_PROG;
+	xdp.command = mode == XDP_MODE_HW ? XDP_SETUP_PROG_HW : XDP_SETUP_PROG;
 	xdp.extack = extack;
 	xdp.flags = flags;
 	xdp.prog = prog;
 
 	err = bpf_op(dev, &xdp);
-	if (!err && non_hw)
-		bpf_prog_change_xdp(prev_prog, prog);
+	if (err)
+		return err;
 
-	if (prev_prog)
-		bpf_prog_put(prev_prog);
+	if (mode != XDP_MODE_HW)
+		bpf_prog_change_xdp(dev_xdp_prog(dev, mode), prog);
 
-	return err;
+	return 0;
 }
 
 static void dev_xdp_uninstall(struct net_device *dev)
 {
-	struct netdev_bpf xdp;
 	bpf_op_t ndo_bpf;
 
 	/* Remove generic XDP */
-	WARN_ON(dev_xdp_install(dev, generic_xdp_install, NULL, 0, NULL));
+	WARN_ON(dev_xdp_install(dev, XDP_MODE_SKB, generic_xdp_install,
+				NULL, 0, NULL));
+	dev_xdp_set_prog(dev, XDP_MODE_SKB, NULL);
 
 	/* Remove from the driver */
 	ndo_bpf = dev->netdev_ops->ndo_bpf;
 	if (!ndo_bpf)
 		return;
 
-	memset(&xdp, 0, sizeof(xdp));
-	xdp.command = XDP_QUERY_PROG;
-	WARN_ON(ndo_bpf(dev, &xdp));
-	if (xdp.prog_id)
-		WARN_ON(dev_xdp_install(dev, ndo_bpf, NULL, xdp.prog_flags,
-					NULL));
+	if (dev_xdp_prog_id(dev, XDP_MODE_DRV)) {
+		WARN_ON(dev_xdp_install(dev, XDP_MODE_DRV, ndo_bpf,
+					NULL, 0, NULL));
+		dev_xdp_set_prog(dev, XDP_MODE_DRV, NULL);
+	}
 
 	/* Remove HW offload */
-	memset(&xdp, 0, sizeof(xdp));
-	xdp.command = XDP_QUERY_PROG_HW;
-	if (!ndo_bpf(dev, &xdp) && xdp.prog_id)
-		WARN_ON(dev_xdp_install(dev, ndo_bpf, NULL, xdp.prog_flags,
-					NULL));
+	if (dev_xdp_prog_id(dev, XDP_MODE_HW)) {
+		WARN_ON(dev_xdp_install(dev, XDP_MODE_HW, ndo_bpf,
+					NULL, 0, NULL));
+		dev_xdp_set_prog(dev, XDP_MODE_HW, NULL);
+	}
+}
+
+static enum bpf_xdp_mode xdp_flags_to_mode(u32 flags)
+{
+	if (flags & XDP_FLAGS_HW_MODE)
+		return XDP_MODE_HW;
+	if (flags & XDP_FLAGS_DRV_MODE)
+		return XDP_MODE_DRV;
+	return XDP_MODE_SKB;
 }
 
 /**
@@ -8807,29 +8805,26 @@ int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
 		      int fd, int expected_fd, u32 flags)
 {
 	const struct net_device_ops *ops = dev->netdev_ops;
-	enum bpf_netdev_command query;
+	enum bpf_xdp_mode mode = xdp_flags_to_mode(flags);
+	bool offload = mode == XDP_MODE_HW;
 	u32 prog_id, expected_id = 0;
 	bpf_op_t bpf_op, bpf_chk;
 	struct bpf_prog *prog;
-	bool offload;
 	int err;
 
 	ASSERT_RTNL();
 
-	offload = flags & XDP_FLAGS_HW_MODE;
-	query = offload ? XDP_QUERY_PROG_HW : XDP_QUERY_PROG;
-
 	bpf_op = bpf_chk = ops->ndo_bpf;
-	if (!bpf_op && (flags & (XDP_FLAGS_DRV_MODE | XDP_FLAGS_HW_MODE))) {
+	if (!bpf_op && (mode == XDP_MODE_DRV || mode == XDP_MODE_HW)) {
 		NL_SET_ERR_MSG(extack, "underlying driver does not support XDP in native mode");
 		return -EOPNOTSUPP;
 	}
-	if (!bpf_op || (flags & XDP_FLAGS_SKB_MODE))
+	if (!bpf_op || mode == XDP_MODE_SKB)
 		bpf_op = generic_xdp_install;
 	if (bpf_op == bpf_chk)
 		bpf_chk = generic_xdp_install;
 
-	prog_id = __dev_xdp_query(dev, bpf_op, query);
+	prog_id = dev_xdp_prog_id(dev, mode);
 	if (flags & XDP_FLAGS_REPLACE) {
 		if (expected_fd >= 0) {
 			prog = bpf_prog_get_type_dev(expected_fd,
@@ -8847,7 +8842,8 @@ int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
 		}
 	}
 	if (fd >= 0) {
-		if (!offload && __dev_xdp_query(dev, bpf_chk, XDP_QUERY_PROG)) {
+		/* XDP_MODE_SKB == 1 - XDP_MODE_DRV */
+		if (!offload && dev_xdp_prog_id(dev, 1 - mode)) {
 			NL_SET_ERR_MSG(extack, "native and generic XDP can't be active at the same time");
 			return -EEXIST;
 		}
@@ -8885,11 +8881,14 @@ int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
 		prog = NULL;
 	}
 
-	err = dev_xdp_install(dev, bpf_op, extack, flags, prog);
-	if (err < 0 && prog)
+	err = dev_xdp_install(dev, mode, bpf_op, extack, flags, prog);
+	if (err < 0 && prog) {
 		bpf_prog_put(prog);
+		return err;
+	}
+	dev_xdp_set_prog(dev, mode, prog);
 
-	return err;
+	return 0;
 }
 
 /**
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 9aedc15736ad..754fdfafacb0 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1416,13 +1416,12 @@ static u32 rtnl_xdp_prog_skb(struct net_device *dev)
 
 static u32 rtnl_xdp_prog_drv(struct net_device *dev)
 {
-	return __dev_xdp_query(dev, dev->netdev_ops->ndo_bpf, XDP_QUERY_PROG);
+	return dev_xdp_prog_id(dev, XDP_MODE_DRV);
 }
 
 static u32 rtnl_xdp_prog_hw(struct net_device *dev)
 {
-	return __dev_xdp_query(dev, dev->netdev_ops->ndo_bpf,
-			       XDP_QUERY_PROG_HW);
+	return dev_xdp_prog_id(dev, XDP_MODE_HW);
 }
 
 static int rtnl_xdp_report_one(struct sk_buff *skb, struct net_device *dev,
-- 
2.24.1

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