[xdp-hints] [RFC bpf-next v2 12/24] xdp: Add checksum hint

[Larysa Zaremba <larysa.zaremba@intel.com>]

Implement functionality that enables drivers to expose to XDP code checksum
information that consists of:

- Checksum status - 2 non-exlusive flags:
  - XDP_CHECKSUM_VERIFIED indicating HW has validated the checksum
    (corresponding to CHECKSUM_UNNECESSARY in sk_buff)
  - XDP_CHECKSUM_COMPLETE signifies the validity of the second argument
    (corresponding to CHECKSUM_COMPLETE in sk_buff)
- Checksum, calculated over the entire packet, valid if the second flag is
  set

Acked-by: Stanislav Fomichev <sdf@google.com>
Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
---
 Documentation/networking/xdp-rx-metadata.rst |  3 +++
 include/net/xdp.h                            | 17 +++++++++++++++
 include/uapi/linux/netdev.h                  |  5 ++++-
 net/core/xdp.c                               | 23 ++++++++++++++++++++
 tools/include/uapi/linux/netdev.h            |  5 ++++-
 5 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/Documentation/networking/xdp-rx-metadata.rst b/Documentation/networking/xdp-rx-metadata.rst
index bb53b00d1b2c..af603568e560 100644
--- a/Documentation/networking/xdp-rx-metadata.rst
+++ b/Documentation/networking/xdp-rx-metadata.rst
@@ -26,6 +26,9 @@ metadata is supported, this set will grow:
 .. kernel-doc:: net/core/xdp.c
    :identifiers: bpf_xdp_metadata_rx_vlan_tag
 
+.. kernel-doc:: net/core/xdp.c
+   :identifiers: bpf_xdp_metadata_rx_csum
+
 An XDP program can use these kfuncs to read the metadata into stack
 variables for its own consumption. Or, to pass the metadata on to other
 consumers, an XDP program can store it into the metadata area carried
diff --git a/include/net/xdp.h b/include/net/xdp.h
index ef79f124dbcf..1dba8ab6c6ba 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -403,6 +403,10 @@ void xdp_attachment_setup(struct xdp_attachment_info *info,
 			   NETDEV_XDP_RX_METADATA_VLAN_TAG, \
 			   bpf_xdp_metadata_rx_vlan_tag, \
 			   xmo_rx_vlan_tag) \
+	XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_CSUM, \
+			   NETDEV_XDP_RX_METADATA_CSUM, \
+			   bpf_xdp_metadata_rx_csum, \
+			   xmo_rx_csum) \
 
 enum xdp_rx_metadata {
 #define XDP_METADATA_KFUNC(name, _, __, ___) name,
@@ -460,12 +464,25 @@ enum xdp_rss_hash_type {
 	XDP_RSS_TYPE_L4_IPV6_SCTP_EX = XDP_RSS_TYPE_L4_IPV6_SCTP | XDP_RSS_L3_DYNHDR,
 };
 
+enum xdp_csum_status {
+	/* HW had parsed headers and validated the outermost checksum,
+	 * same as ``CHECKSUM_UNNECESSARY`` in ``sk_buff``.
+	 */
+	XDP_CHECKSUM_VERIFIED		= BIT(0),
+
+	/* Checksum, calculated over the entire packet is provided */
+	XDP_CHECKSUM_COMPLETE		= BIT(1),
+};
+
 struct xdp_metadata_ops {
 	int	(*xmo_rx_timestamp)(const struct xdp_md *ctx, u64 *timestamp);
 	int	(*xmo_rx_hash)(const struct xdp_md *ctx, u32 *hash,
 			       enum xdp_rss_hash_type *rss_type);
 	int	(*xmo_rx_vlan_tag)(const struct xdp_md *ctx, __be16 *vlan_proto,
 				   u16 *vlan_tci);
+	int	(*xmo_rx_csum)(const struct xdp_md *ctx,
+			       enum xdp_csum_status *csum_status,
+			       __wsum *csum);
 };
 
 #ifdef CONFIG_NET
diff --git a/include/uapi/linux/netdev.h b/include/uapi/linux/netdev.h
index 661f603e3e43..ef477d7391e2 100644
--- a/include/uapi/linux/netdev.h
+++ b/include/uapi/linux/netdev.h
@@ -46,14 +46,17 @@ enum netdev_xdp_act {
  *   hash via bpf_xdp_metadata_rx_hash().
  * @NETDEV_XDP_RX_METADATA_VLAN_TAG: Device is capable of exposing stripped
  *   receive VLAN tag (proto and TCI) via bpf_xdp_metadata_rx_vlan_tag().
+ * @NETDEV_XDP_RX_METADATA_CSUM: Device is capable of exposing receive checksum
+     information via bpf_xdp_metadata_rx_csum().
  */
 enum netdev_xdp_rx_metadata {
 	NETDEV_XDP_RX_METADATA_TIMESTAMP = 1,
 	NETDEV_XDP_RX_METADATA_HASH = 2,
 	NETDEV_XDP_RX_METADATA_VLAN_TAG = 4,
+	NETDEV_XDP_RX_METADATA_CSUM = 8,
 
 	/* private: */
-	NETDEV_XDP_RX_METADATA_MASK = 7,
+	NETDEV_XDP_RX_METADATA_MASK = 15,
 };
 
 enum {
diff --git a/net/core/xdp.c b/net/core/xdp.c
index fb87925b3dc3..9e6fc52b3dca 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -771,6 +771,29 @@ __bpf_kfunc int bpf_xdp_metadata_rx_vlan_tag(const struct xdp_md *ctx,
 	return -EOPNOTSUPP;
 }
 
+/**
+ * bpf_xdp_metadata_rx_csum - Get checksum status with additional info.
+ * @ctx: XDP context pointer.
+ * @csum_status: Destination for checksum status.
+ * @csum: Destination for complete checksum.
+ *
+ * Status (@csum_status) is a bitfield that informs, what checksum
+ * processing was performed. If ``XDP_CHECKSUM_COMPLETE`` in status is set,
+ * second argument (@csum) contains a checksum, calculated over the entire
+ * packet.
+ *
+ * Return:
+ * * Returns 0 on success or ``-errno`` on error.
+ * * ``-EOPNOTSUPP`` : device driver doesn't implement kfunc
+ * * ``-ENODATA``    : Checksum status is unknown
+ */
+__bpf_kfunc int bpf_xdp_metadata_rx_csum(const struct xdp_md *ctx,
+					 enum xdp_csum_status *csum_status,
+					 __wsum *csum)
+{
+	return -EOPNOTSUPP;
+}
+
 __diag_pop();
 
 BTF_SET8_START(xdp_metadata_kfunc_ids)
diff --git a/tools/include/uapi/linux/netdev.h b/tools/include/uapi/linux/netdev.h
index 661f603e3e43..ef477d7391e2 100644
--- a/tools/include/uapi/linux/netdev.h
+++ b/tools/include/uapi/linux/netdev.h
@@ -46,14 +46,17 @@ enum netdev_xdp_act {
  *   hash via bpf_xdp_metadata_rx_hash().
  * @NETDEV_XDP_RX_METADATA_VLAN_TAG: Device is capable of exposing stripped
  *   receive VLAN tag (proto and TCI) via bpf_xdp_metadata_rx_vlan_tag().
+ * @NETDEV_XDP_RX_METADATA_CSUM: Device is capable of exposing receive checksum
+     information via bpf_xdp_metadata_rx_csum().
  */
 enum netdev_xdp_rx_metadata {
 	NETDEV_XDP_RX_METADATA_TIMESTAMP = 1,
 	NETDEV_XDP_RX_METADATA_HASH = 2,
 	NETDEV_XDP_RX_METADATA_VLAN_TAG = 4,
+	NETDEV_XDP_RX_METADATA_CSUM = 8,
 
 	/* private: */
-	NETDEV_XDP_RX_METADATA_MASK = 7,
+	NETDEV_XDP_RX_METADATA_MASK = 15,
 };
 
 enum {
-- 
2.41.0