[xdp-hints] [PATCH RFC bpf-next 10/52] net, xdp: add ability to specify frame size threshold for XDP metadata

[Alexander Lobakin <alexandr.lobakin@intel.com>]

Add the UAPI and the corresponding kernel part to be able to specify
the frame size which the drivers should start composing metadata
from (if supported).

Instead of having just 1 bit on/off, have the possilibty to set the
threshold for drivers to start composing meta. It helps with the
situations when e.g. lots of traffic receive %XDP_DROP verdict
without looking at the meta. In such cases, the performance on the
small frames (< 96 bytes) can suffer by several Mpps with no
benefits, so setting the threshold of 100-128 makes much sense.
Setting it to 0 or 1 works just like a bitflag, values of 2-14
work like 1, values of SZ_16K+ works like 0.
So, the logics in the drivers should be like:

	if (rx_desc->frame_size >= meta_thresh)
		compose_meta();

	bpf_prog_run_xdp();

The threshold can be set and updated via both BPF link and rtnetlink
(the %IFLA_XDP_META_THRESH attribute) interfaces, got via
&bpf_link_info and is being passed to the drivers inside
&netdev_bpf. net_device_ops::ndo_bpf() is now also being called when
@new_prog == @old_prog && @new_btf_id == @btf_id &&
@new_meta_thresh != @meta_thresh.

Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com>
---
 include/linux/netdevice.h          |  2 ++
 include/net/xdp.h                  |  1 +
 include/uapi/linux/bpf.h           | 10 +++++++-
 include/uapi/linux/if_link.h       |  1 +
 kernel/bpf/syscall.c               |  2 +-
 net/bpf/core.c                     |  1 +
 net/bpf/dev.c                      | 38 +++++++++++++++++++++++-------
 net/core/rtnetlink.c               |  6 +++++
 tools/include/uapi/linux/bpf.h     | 10 +++++++-
 tools/include/uapi/linux/if_link.h |  1 +
 10 files changed, 60 insertions(+), 12 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 2218c1901daf..bc2d82a3d0de 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -985,6 +985,7 @@ struct netdev_bpf {
 		/* XDP_SETUP_PROG */
 		struct {
 			u32 flags;
+			u32 meta_thresh;
 			u64 btf_id;
 			struct bpf_prog *prog;
 			struct netlink_ext_ack *extack;
@@ -3853,6 +3854,7 @@ struct xdp_install_args {
 	struct net_device	*dev;
 	struct netlink_ext_ack	*extack;
 	u32			flags;
+	u32			meta_thresh;
 	u64			btf_id;
 };
 
diff --git a/include/net/xdp.h b/include/net/xdp.h
index 13133c7493bc..7b8ba068d28a 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -401,6 +401,7 @@ static inline bool xdp_metalen_invalid(unsigned long metalen)
 struct xdp_attachment_info {
 	struct bpf_prog *prog;
 	u64 btf_id;
+	u32 meta_thresh;
 	u32 flags;
 };
 
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index c67ddb78915d..372170ded1d8 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1502,6 +1502,10 @@ union bpf_attr {
 			struct {
 				/* target metadata BTF + type ID */
 				__aligned_u64	btf_id;
+				/* frame size to start composing XDP
+				 * metadata from
+				 */
+				__u32		meta_thresh;
 			} xdp;
 		};
 	} link_create;
@@ -1518,6 +1522,10 @@ union bpf_attr {
 			struct {
 				/* new target metadata BTF + type ID */
 				__aligned_u64	new_btf_id;
+				/* new frame size to start composing XDP
+				 * metadata from
+				 */
+				__u32		new_meta_thresh;
 			} xdp;
 		};
 	} link_update;
@@ -6148,7 +6156,7 @@ struct bpf_link_info {
 		} netns;
 		struct {
 			__u32 ifindex;
-			__u32 :32;
+			__u32 meta_thresh;
 			__aligned_u64 btf_id;
 		} xdp;
 	};
diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index 73cdcc86875e..78b448ff1cb7 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -1308,6 +1308,7 @@ enum {
 	IFLA_XDP_HW_PROG_ID,
 	IFLA_XDP_EXPECTED_FD,
 	IFLA_XDP_BTF_ID,
+	IFLA_XDP_META_THRESH,
 	__IFLA_XDP_MAX,
 };
 
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 2e86cfeae10f..e1a56e62bdb4 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -4575,7 +4575,7 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
 	return ret;
 }
 
-#define BPF_LINK_UPDATE_LAST_FIELD link_update.xdp.new_btf_id
+#define BPF_LINK_UPDATE_LAST_FIELD link_update.xdp.new_meta_thresh
 
 static int link_update(union bpf_attr *attr)
 {
diff --git a/net/bpf/core.c b/net/bpf/core.c
index e5abd5a64df7..dcd3b6ae86b7 100644
--- a/net/bpf/core.c
+++ b/net/bpf/core.c
@@ -553,6 +553,7 @@ void xdp_attachment_setup(struct xdp_attachment_info *info,
 		bpf_prog_put(info->prog);
 	info->prog = bpf->prog;
 	info->btf_id = bpf->btf_id;
+	info->meta_thresh = bpf->meta_thresh;
 	info->flags = bpf->flags;
 }
 EXPORT_SYMBOL_GPL(xdp_attachment_setup);
diff --git a/net/bpf/dev.c b/net/bpf/dev.c
index e96986220126..82948d0536c8 100644
--- a/net/bpf/dev.c
+++ b/net/bpf/dev.c
@@ -273,6 +273,7 @@ struct bpf_xdp_link {
 	struct bpf_link link;
 	struct net_device *dev; /* protected by rtnl_lock, no refcnt held */
 	int flags;
+	u32 meta_thresh;
 	u64 btf_id;
 };
 
@@ -358,12 +359,20 @@ static int dev_xdp_install(const struct xdp_install_args *args,
 	struct netdev_bpf xdp;
 	int err;
 
-	/* BTF ID must not be set when uninstalling the program */
-	if (!prog && args->btf_id)
+	/* Neither BTF ID nor meta threshold can be set when uninstalling
+	 * the program
+	 */
+	if (!prog && (args->btf_id || args->meta_thresh))
+		return -EINVAL;
+
+	/* Both meta threshold and BTF ID must be either specified or not */
+	if (!args->btf_id != !args->meta_thresh)
 		return -EINVAL;
 
 	memset(&xdp, 0, sizeof(xdp));
 	xdp.command = mode == XDP_MODE_HW ? XDP_SETUP_PROG_HW : XDP_SETUP_PROG;
+	/* Convert 0 to "infitity" to allow plain >= comparison on hotpath */
+	xdp.meta_thresh = args->meta_thresh ? : ~args->meta_thresh;
 	xdp.btf_id = args->btf_id;
 	xdp.extack = args->extack;
 	xdp.flags = args->flags;
@@ -523,11 +532,13 @@ static int dev_xdp_attach(const struct xdp_install_args *args,
 		}
 	}
 
-	/* don't call drivers if the effective program or BTF ID didn't change.
-	 * If @link == %NULL, we don't know the old value, so the only thing we
-	 * can do is to call installing unconditionally
+	/* don't call drivers if the effective program or BTF ID / metadata
+	 * threshold didn't change. If @link == %NULL, we don't know the
+	 * old values, so the only thing we can do is to call installing
+	 * unconditionally
 	 */
-	if (new_prog != cur_prog || !link || args->btf_id != link->btf_id) {
+	if (new_prog != cur_prog || !link || args->btf_id != link->btf_id ||
+	    args->meta_thresh != link->meta_thresh) {
 		bpf_op = dev_xdp_bpf_op(dev, mode);
 		if (!bpf_op) {
 			NL_SET_ERR_MSG(extack, "Underlying driver does not support XDP in native mode");
@@ -555,6 +566,7 @@ static int dev_xdp_attach_link(struct bpf_xdp_link *link)
 		.dev		= link->dev,
 		.flags		= link->flags,
 		.btf_id		= link->btf_id,
+		.meta_thresh	= link->meta_thresh,
 	};
 
 	return dev_xdp_attach(&args, link, NULL, NULL);
@@ -615,16 +627,18 @@ static void bpf_xdp_link_show_fdinfo(const struct bpf_link *link,
 				     struct seq_file *seq)
 {
 	struct bpf_xdp_link *xdp_link = container_of(link, struct bpf_xdp_link, link);
-	u32 ifindex = 0;
+	u32 meta_thresh, ifindex = 0;
 	u64 btf_id;
 
 	rtnl_lock();
 	if (xdp_link->dev)
 		ifindex = xdp_link->dev->ifindex;
+	meta_thresh = xdp_link->meta_thresh;
 	btf_id = xdp_link->btf_id;
 	rtnl_unlock();
 
 	seq_printf(seq, "ifindex:\t%u\n", ifindex);
+	seq_printf(seq, "meta_thresh:\t%u\n", meta_thresh);
 	seq_printf(seq, "btf_id:\t0x%llx\n", btf_id);
 }
 
@@ -632,17 +646,19 @@ static int bpf_xdp_link_fill_link_info(const struct bpf_link *link,
 				       struct bpf_link_info *info)
 {
 	struct bpf_xdp_link *xdp_link = container_of(link, struct bpf_xdp_link, link);
-	u32 ifindex = 0;
+	u32 meta_thresh, ifindex = 0;
 	u64 btf_id;
 
 	rtnl_lock();
 	if (xdp_link->dev)
 		ifindex = xdp_link->dev->ifindex;
+	meta_thresh = xdp_link->meta_thresh;
 	btf_id = xdp_link->btf_id;
 	rtnl_unlock();
 
 	info->xdp.ifindex = ifindex;
 	info->xdp.btf_id = btf_id;
+	info->xdp.meta_thresh = meta_thresh;
 	return 0;
 }
 
@@ -656,6 +672,7 @@ static int bpf_xdp_link_update(struct bpf_link *link,
 		.dev		= xdp_link->dev,
 		.flags		= xdp_link->flags,
 		.btf_id		= attr->link_update.xdp.new_btf_id,
+		.meta_thresh	= attr->link_update.xdp.new_meta_thresh,
 	};
 	enum bpf_xdp_mode mode;
 	bpf_op_t bpf_op;
@@ -680,7 +697,8 @@ static int bpf_xdp_link_update(struct bpf_link *link,
 		goto out_unlock;
 	}
 
-	if (old_prog == new_prog && args.btf_id == xdp_link->btf_id) {
+	if (old_prog == new_prog && args.btf_id == xdp_link->btf_id &&
+	    args.meta_thresh == xdp_link->meta_thresh) {
 		/* no-op, don't disturb drivers */
 		bpf_prog_put(new_prog);
 		goto out_unlock;
@@ -696,6 +714,7 @@ static int bpf_xdp_link_update(struct bpf_link *link,
 	bpf_prog_put(old_prog);
 
 	xdp_link->btf_id = args.btf_id;
+	xdp_link->meta_thresh = args.meta_thresh;
 
 out_unlock:
 	rtnl_unlock();
@@ -736,6 +755,7 @@ int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 	link->dev = dev;
 	link->flags = attr->link_create.flags;
 	link->btf_id = attr->link_create.xdp.btf_id;
+	link->meta_thresh = attr->link_create.xdp.meta_thresh;
 
 	err = bpf_link_prime(&link->link, &link_primer);
 	if (err) {
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index a30723b0e50c..500420d5017c 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1980,6 +1980,7 @@ static const struct nla_policy ifla_xdp_policy[IFLA_XDP_MAX + 1] = {
 	[IFLA_XDP_FLAGS]	= { .type = NLA_U32 },
 	[IFLA_XDP_PROG_ID]	= { .type = NLA_U32 },
 	[IFLA_XDP_BTF_ID]	= { .type = NLA_U64 },
+	[IFLA_XDP_META_THRESH]	= { .type = NLA_U32 },
 };
 
 static const struct rtnl_link_ops *linkinfo_to_kind_ops(const struct nlattr *nla)
@@ -2962,6 +2963,7 @@ static int do_setlink(const struct sk_buff *skb,
 
 	if (tb[IFLA_XDP]) {
 		struct nlattr *xdp[IFLA_XDP_MAX + 1];
+		u32 meta_thresh = 0;
 		u32 xdp_flags = 0;
 		u64 btf_id = 0;
 
@@ -2991,12 +2993,16 @@ static int do_setlink(const struct sk_buff *skb,
 		if (xdp[IFLA_XDP_BTF_ID])
 			btf_id = nla_get_u64(xdp[IFLA_XDP_BTF_ID]);
 
+		if (xdp[IFLA_XDP_META_THRESH])
+			meta_thresh = nla_get_u32(xdp[IFLA_XDP_META_THRESH]);
+
 		if (xdp[IFLA_XDP_FD]) {
 			struct xdp_install_args args = {
 				.dev		= dev,
 				.extack		= extack,
 				.btf_id		= btf_id,
 				.flags		= xdp_flags,
+				.meta_thresh	= meta_thresh,
 			};
 			int expected_fd = -1;
 
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index c67ddb78915d..372170ded1d8 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1502,6 +1502,10 @@ union bpf_attr {
 			struct {
 				/* target metadata BTF + type ID */
 				__aligned_u64	btf_id;
+				/* frame size to start composing XDP
+				 * metadata from
+				 */
+				__u32		meta_thresh;
 			} xdp;
 		};
 	} link_create;
@@ -1518,6 +1522,10 @@ union bpf_attr {
 			struct {
 				/* new target metadata BTF + type ID */
 				__aligned_u64	new_btf_id;
+				/* new frame size to start composing XDP
+				 * metadata from
+				 */
+				__u32		new_meta_thresh;
 			} xdp;
 		};
 	} link_update;
@@ -6148,7 +6156,7 @@ struct bpf_link_info {
 		} netns;
 		struct {
 			__u32 ifindex;
-			__u32 :32;
+			__u32 meta_thresh;
 			__aligned_u64 btf_id;
 		} xdp;
 	};
diff --git a/tools/include/uapi/linux/if_link.h b/tools/include/uapi/linux/if_link.h
index 68b126678dc8..b73b9c0f06fb 100644
--- a/tools/include/uapi/linux/if_link.h
+++ b/tools/include/uapi/linux/if_link.h
@@ -1213,6 +1213,7 @@ enum {
 	IFLA_XDP_HW_PROG_ID,
 	IFLA_XDP_EXPECTED_FD,
 	IFLA_XDP_BTF_ID,
+	IFLA_XDP_META_THRESH,
 	__IFLA_XDP_MAX,
 };
 
-- 
2.36.1