sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 287 insertions, 0 deletions

diff --git a/net/ipv4/gre_offload.c b/net/ipv4/gre_offload.c
new file mode 100644
index 000000000..5028c72d4
--- /dev/null
+++ b/net/ipv4/gre_offload.c
@@ -0,0 +1,287 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *	IPV4 GSO/GRO offload support
+ *	Linux INET implementation
+ *
+ *	GRE GSO support
+ */
+
+#include <linux/skbuff.h>
+#include <linux/init.h>
+#include <net/protocol.h>
+#include <net/gre.h>
+#include <net/gro.h>
+#include <net/gso.h>
+
+static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
+				       netdev_features_t features)
+{
+	int tnl_hlen = skb_inner_mac_header(skb) - skb_transport_header(skb);
+	bool need_csum, offload_csum, gso_partial, need_ipsec;
+	struct sk_buff *segs = ERR_PTR(-EINVAL);
+	u16 mac_offset = skb->mac_header;
+	__be16 protocol = skb->protocol;
+	u16 mac_len = skb->mac_len;
+	int gre_offset, outer_hlen;
+
+	if (!skb->encapsulation)
+		goto out;
+
+	if (unlikely(tnl_hlen < sizeof(struct gre_base_hdr)))
+		goto out;
+
+	if (unlikely(!pskb_may_pull(skb, tnl_hlen)))
+		goto out;
+
+	/* setup inner skb. */
+	skb->encapsulation = 0;
+	SKB_GSO_CB(skb)->encap_level = 0;
+	__skb_pull(skb, tnl_hlen);
+	skb_reset_mac_header(skb);
+	skb_set_network_header(skb, skb_inner_network_offset(skb));
+	skb->mac_len = skb_inner_network_offset(skb);
+	skb->protocol = skb->inner_protocol;
+
+	need_csum = !!(skb_shinfo(skb)->gso_type & SKB_GSO_GRE_CSUM);
+	skb->encap_hdr_csum = need_csum;
+
+	features &= skb->dev->hw_enc_features;
+	if (need_csum)
+		features &= ~NETIF_F_SCTP_CRC;
+
+	need_ipsec = skb_dst(skb) && dst_xfrm(skb_dst(skb));
+	/* Try to offload checksum if possible */
+	offload_csum = !!(need_csum && !need_ipsec &&
+			  (skb->dev->features & NETIF_F_HW_CSUM));
+
+	/* segment inner packet. */
+	segs = skb_mac_gso_segment(skb, features);
+	if (IS_ERR_OR_NULL(segs)) {
+		skb_gso_error_unwind(skb, protocol, tnl_hlen, mac_offset,
+				     mac_len);
+		goto out;
+	}
+
+	gso_partial = !!(skb_shinfo(segs)->gso_type & SKB_GSO_PARTIAL);
+
+	outer_hlen = skb_tnl_header_len(skb);
+	gre_offset = outer_hlen - tnl_hlen;
+	skb = segs;
+	do {
+		struct gre_base_hdr *greh;
+		__sum16 *pcsum;
+
+		/* Set up inner headers if we are offloading inner checksum */
+		if (skb->ip_summed == CHECKSUM_PARTIAL) {
+			skb_reset_inner_headers(skb);
+			skb->encapsulation = 1;
+		}
+
+		skb->mac_len = mac_len;
+		skb->protocol = protocol;
+
+		__skb_push(skb, outer_hlen);
+		skb_reset_mac_header(skb);
+		skb_set_network_header(skb, mac_len);
+		skb_set_transport_header(skb, gre_offset);
+
+		if (!need_csum)
+			continue;
+
+		greh = (struct gre_base_hdr *)skb_transport_header(skb);
+		pcsum = (__sum16 *)(greh + 1);
+
+		if (gso_partial && skb_is_gso(skb)) {
+			unsigned int partial_adj;
+
+			/* Adjust checksum to account for the fact that
+			 * the partial checksum is based on actual size
+			 * whereas headers should be based on MSS size.
+			 */
+			partial_adj = skb->len + skb_headroom(skb) -
+				      SKB_GSO_CB(skb)->data_offset -
+				      skb_shinfo(skb)->gso_size;
+			*pcsum = ~csum_fold((__force __wsum)htonl(partial_adj));
+		} else {
+			*pcsum = 0;
+		}
+
+		*(pcsum + 1) = 0;
+		if (skb->encapsulation || !offload_csum) {
+			*pcsum = gso_make_checksum(skb, 0);
+		} else {
+			skb->ip_summed = CHECKSUM_PARTIAL;
+			skb->csum_start = skb_transport_header(skb) - skb->head;
+			skb->csum_offset = sizeof(*greh);
+		}
+	} while ((skb = skb->next));
+out:
+	return segs;
+}
+
+static struct sk_buff *gre_gro_receive(struct list_head *head,
+				       struct sk_buff *skb)
+{
+	struct sk_buff *pp = NULL;
+	struct sk_buff *p;
+	const struct gre_base_hdr *greh;
+	unsigned int hlen, grehlen;
+	unsigned int off;
+	int flush = 1;
+	struct packet_offload *ptype;
+	__be16 type;
+
+	if (NAPI_GRO_CB(skb)->encap_mark)
+		goto out;
+
+	NAPI_GRO_CB(skb)->encap_mark = 1;
+
+	off = skb_gro_offset(skb);
+	hlen = off + sizeof(*greh);
+	greh = skb_gro_header(skb, hlen, off);
+	if (unlikely(!greh))
+		goto out;
+
+	/* Only support version 0 and K (key), C (csum) flags. Note that
+	 * although the support for the S (seq#) flag can be added easily
+	 * for GRO, this is problematic for GSO hence can not be enabled
+	 * here because a GRO pkt may end up in the forwarding path, thus
+	 * requiring GSO support to break it up correctly.
+	 */
+	if ((greh->flags & ~(GRE_KEY|GRE_CSUM)) != 0)
+		goto out;
+
+	/* We can only support GRE_CSUM if we can track the location of
+	 * the GRE header.  In the case of FOU/GUE we cannot because the
+	 * outer UDP header displaces the GRE header leaving us in a state
+	 * of limbo.
+	 */
+	if ((greh->flags & GRE_CSUM) && NAPI_GRO_CB(skb)->is_fou)
+		goto out;
+
+	type = greh->protocol;
+
+	ptype = gro_find_receive_by_type(type);
+	if (!ptype)
+		goto out;
+
+	grehlen = GRE_HEADER_SECTION;
+
+	if (greh->flags & GRE_KEY)
+		grehlen += GRE_HEADER_SECTION;
+
+	if (greh->flags & GRE_CSUM)
+		grehlen += GRE_HEADER_SECTION;
+
+	hlen = off + grehlen;
+	if (!skb_gro_may_pull(skb, hlen)) {
+		greh = skb_gro_header_slow(skb, hlen, off);
+		if (unlikely(!greh))
+			goto out;
+	}
+
+	/* Don't bother verifying checksum if we're going to flush anyway. */
+	if ((greh->flags & GRE_CSUM) && !NAPI_GRO_CB(skb)->flush) {
+		if (skb_gro_checksum_simple_validate(skb))
+			goto out;
+
+		skb_gro_checksum_try_convert(skb, IPPROTO_GRE,
+					     null_compute_pseudo);
+	}
+
+	list_for_each_entry(p, head, list) {
+		const struct gre_base_hdr *greh2;
+
+		if (!NAPI_GRO_CB(p)->same_flow)
+			continue;
+
+		/* The following checks are needed to ensure only pkts
+		 * from the same tunnel are considered for aggregation.
+		 * The criteria for "the same tunnel" includes:
+		 * 1) same version (we only support version 0 here)
+		 * 2) same protocol (we only support ETH_P_IP for now)
+		 * 3) same set of flags
+		 * 4) same key if the key field is present.
+		 */
+		greh2 = (struct gre_base_hdr *)(p->data + off);
+
+		if (greh2->flags != greh->flags ||
+		    greh2->protocol != greh->protocol) {
+			NAPI_GRO_CB(p)->same_flow = 0;
+			continue;
+		}
+		if (greh->flags & GRE_KEY) {
+			/* compare keys */
+			if (*(__be32 *)(greh2+1) != *(__be32 *)(greh+1)) {
+				NAPI_GRO_CB(p)->same_flow = 0;
+				continue;
+			}
+		}
+	}
+
+	skb_gro_pull(skb, grehlen);
+
+	/* Adjusted NAPI_GRO_CB(skb)->csum after skb_gro_pull()*/
+	skb_gro_postpull_rcsum(skb, greh, grehlen);
+
+	pp = call_gro_receive(ptype->callbacks.gro_receive, head, skb);
+	flush = 0;
+
+out:
+	skb_gro_flush_final(skb, pp, flush);
+
+	return pp;
+}
+
+static int gre_gro_complete(struct sk_buff *skb, int nhoff)
+{
+	struct gre_base_hdr *greh = (struct gre_base_hdr *)(skb->data + nhoff);
+	struct packet_offload *ptype;
+	unsigned int grehlen = sizeof(*greh);
+	int err = -ENOENT;
+	__be16 type;
+
+	skb->encapsulation = 1;
+	skb_shinfo(skb)->gso_type = SKB_GSO_GRE;
+
+	type = greh->protocol;
+	if (greh->flags & GRE_KEY)
+		grehlen += GRE_HEADER_SECTION;
+
+	if (greh->flags & GRE_CSUM)
+		grehlen += GRE_HEADER_SECTION;
+
+	ptype = gro_find_complete_by_type(type);
+	if (ptype)
+		err = ptype->callbacks.gro_complete(skb, nhoff + grehlen);
+
+	skb_set_inner_mac_header(skb, nhoff + grehlen);
+
+	return err;
+}
+
+static const struct net_offload gre_offload = {
+	.callbacks = {
+		.gso_segment = gre_gso_segment,
+		.gro_receive = gre_gro_receive,
+		.gro_complete = gre_gro_complete,
+	},
+};
+
+static int __init gre_offload_init(void)
+{
+	int err;
+
+	err = inet_add_offload(&gre_offload, IPPROTO_GRE);
+#if IS_ENABLED(CONFIG_IPV6)
+	if (err)
+		return err;
+
+	err = inet6_add_offload(&gre_offload, IPPROTO_GRE);
+	if (err)
+		inet_del_offload(&gre_offload, IPPROTO_GRE);
+#endif
+
+	return err;
+}
+device_initcall(gre_offload_init);