[RFC bpf-next 0/4] add partial rx hw csum offload support for XDP

12 messages, 5 authors, 2021-05-31 · open the first message on its own page

[RFC bpf-next 0/4] add partial rx hw csum offload support for XDP

From: Lorenzo Bianconi <lorenzo@kernel.org>
Date: 2021-05-28 17:44:03

Enable xdp rx checksum offload support for CHECKSUM_UNNECESSARY use-case.
Introduce flag field in xdp_buff/xdp_frame in order to save the checksum
result from the NIC and have a fast access to it performing XDP_REDIRECT.
CHECKSUM_COMPLETE is not supported yet since it will require adding the
csum result to the xdp_metadata area.
Moreover flag field will be reused for xdp multi-buff support.
This series has been tested generating UDP traffic with pktgen and performing
a xdp_redirect from an ixgbe device to a remote CPUMAP entry. PPS results show
a negligible penalty respect to the baseline where the UDP checksum has been
disabled. More info about the test can be found here [0].

[0] https://github.com/xdp-project/xdp-project/blob/master/areas/core/xdp_frame01_checksum.org

Lorenzo Bianconi (4):
  net: xdp: introduce flags field in xdp_buff and xdp_frame
  mvneta: return csum computation result from mvneta_rx_csum
  net: mvneta: report csum result in xdp_buff
  net: xdp: update csum building the skb

 drivers/net/ethernet/marvell/mvneta.c | 27 ++++++++------------
 include/net/xdp.h                     | 36 +++++++++++++++++++++++++++
 net/core/xdp.c                        |  2 +-
 3 files changed, 48 insertions(+), 17 deletions(-)

-- 
2.31.1

[RFC bpf-next 1/4] net: xdp: introduce flags field in xdp_buff and xdp_frame

From: Lorenzo Bianconi <lorenzo@kernel.org>
Date: 2021-05-28 17:44:10

Introduce flag field in xdp_buff and xdp_frame data structure in order
to report xdp_buffer metadata. For the moment just hw checksum hints
are defined but flags field will be reused for xdp multi-buffer
For the moment just CHECKSUM_UNNECESSARY is supported.
CHECKSUM_COMPLETE will need to set csum value in metada space.

Co-developed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 include/net/xdp.h | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/include/net/xdp.h b/include/net/xdp.h
index 5533f0ab2afc..e81ac505752b 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h

@@ -66,6 +66,13 @@ struct xdp_txq_info {
 	struct net_device *dev;
 };
 
+/* xdp metadata bitmask */
+#define XDP_CSUM_MASK		GENMASK(1, 0)
+enum xdp_flags {
+	XDP_CSUM_UNNECESSARY	= BIT(0),
+	XDP_CSUM_COMPLETE	= BIT(1),
+};
+
 struct xdp_buff {
 	void *data;
 	void *data_end;

@@ -74,6 +81,7 @@ struct xdp_buff {
 	struct xdp_rxq_info *rxq;
 	struct xdp_txq_info *txq;
 	u32 frame_sz; /* frame size to deduce data_hard_end/reserved tailroom*/
+	u16 flags; /* xdp_flags */
 };
 
 static __always_inline void

@@ -81,6 +89,7 @@ xdp_init_buff(struct xdp_buff *xdp, u32 frame_sz, struct xdp_rxq_info *rxq)
 {
 	xdp->frame_sz = frame_sz;
 	xdp->rxq = rxq;
+	xdp->flags = 0;
 }
 
 static __always_inline void

@@ -95,6 +104,18 @@ xdp_prepare_buff(struct xdp_buff *xdp, unsigned char *hard_start,
 	xdp->data_meta = meta_valid ? data : data + 1;
 }
 
+static __always_inline void
+xdp_buff_get_csum(struct xdp_buff *xdp, struct sk_buff *skb)
+{
+	switch (xdp->flags & XDP_CSUM_MASK) {
+	case XDP_CSUM_UNNECESSARY:
+		skb->ip_summed = CHECKSUM_UNNECESSARY;
+		break;
+	default:
+		break;
+	}
+}
+
 /* Reserve memory area at end-of data area.
  *
  * This macro reserves tailroom in the XDP buffer by limiting the

@@ -122,8 +143,21 @@ struct xdp_frame {
 	 */
 	struct xdp_mem_info mem;
 	struct net_device *dev_rx; /* used by cpumap */
+	u16 flags; /* xdp_flags */
 };
 
+static __always_inline void
+xdp_frame_get_csum(struct xdp_frame *xdpf, struct sk_buff *skb)
+{
+	switch (xdpf->flags & XDP_CSUM_MASK) {
+	case XDP_CSUM_UNNECESSARY:
+		skb->ip_summed = CHECKSUM_UNNECESSARY;
+		break;
+	default:
+		break;
+	}
+}
+
 #define XDP_BULK_QUEUE_SIZE	16
 struct xdp_frame_bulk {
 	int count;

@@ -180,6 +214,7 @@ void xdp_convert_frame_to_buff(struct xdp_frame *frame, struct xdp_buff *xdp)
 	xdp->data_end = frame->data + frame->len;
 	xdp->data_meta = frame->data - frame->metasize;
 	xdp->frame_sz = frame->frame_sz;
+	xdp->flags = frame->flags;
 }
 
 static inline

@@ -206,6 +241,7 @@ int xdp_update_frame_from_buff(struct xdp_buff *xdp,
 	xdp_frame->headroom = headroom - sizeof(*xdp_frame);
 	xdp_frame->metasize = metasize;
 	xdp_frame->frame_sz = xdp->frame_sz;
+	xdp_frame->flags = xdp->flags;
 
 	return 0;
 }

-- 
2.31.1

[RFC bpf-next 2/4] mvneta: return csum computation result from mvneta_rx_csum

From: Lorenzo Bianconi <lorenzo@kernel.org>
Date: 2021-05-28 17:44:18

This is a preliminary patch to add hw csum hint support to mvneta xdp
implementation

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 drivers/net/ethernet/marvell/mvneta.c | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index 7d5cd9bc6c99..4a7c153a2666 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c

@@ -1805,18 +1805,14 @@ static void mvneta_rx_error(struct mvneta_port *pp,
 }
 
 /* Handle RX checksum offload based on the descriptor's status */
-static void mvneta_rx_csum(struct mvneta_port *pp, u32 status,
-			   struct sk_buff *skb)
+static int mvneta_rx_csum(struct mvneta_port *pp, u32 status)
 {
 	if ((pp->dev->features & NETIF_F_RXCSUM) &&
 	    (status & MVNETA_RXD_L3_IP4) &&
-	    (status & MVNETA_RXD_L4_CSUM_OK)) {
-		skb->csum = 0;
-		skb->ip_summed = CHECKSUM_UNNECESSARY;
-		return;
-	}
+	    (status & MVNETA_RXD_L4_CSUM_OK))
+		return CHECKSUM_UNNECESSARY;
 
-	skb->ip_summed = CHECKSUM_NONE;
+	return CHECKSUM_NONE;
 }
 
 /* Return tx queue pointer (find last set bit) according to <cause> returned

@@ -2335,7 +2331,7 @@ mvneta_swbm_build_skb(struct mvneta_port *pp, struct mvneta_rx_queue *rxq,
 
 	skb_reserve(skb, xdp->data - xdp->data_hard_start);
 	skb_put(skb, xdp->data_end - xdp->data);
-	mvneta_rx_csum(pp, desc_status, skb);
+	skb->ip_summed = mvneta_rx_csum(pp, desc_status);
 
 	for (i = 0; i < num_frags; i++) {
 		skb_frag_t *frag = &sinfo->frags[i];

@@ -2532,7 +2528,7 @@ static int mvneta_rx_hwbm(struct napi_struct *napi,
 				     rx_bytes);
 
 			skb->protocol = eth_type_trans(skb, dev);
-			mvneta_rx_csum(pp, rx_status, skb);
+			skb->ip_summed = mvneta_rx_csum(pp, rx_status);
 			napi_gro_receive(napi, skb);
 
 			rcvd_pkts++;

@@ -2581,8 +2577,7 @@ static int mvneta_rx_hwbm(struct napi_struct *napi,
 		skb_put(skb, rx_bytes);
 
 		skb->protocol = eth_type_trans(skb, dev);
-
-		mvneta_rx_csum(pp, rx_status, skb);
+		skb->ip_summed = mvneta_rx_csum(pp, rx_status);
 
 		napi_gro_receive(napi, skb);
 	}

-- 
2.31.1

[RFC bpf-next 3/4] net: mvneta: report csum result in xdp_buff

From: Lorenzo Bianconi <lorenzo@kernel.org>
Date: 2021-05-28 17:44:20

This patch allows reusing hw rx csum offloading performing XDP_REDIRECT
from the mvneta driver

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 drivers/net/ethernet/marvell/mvneta.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index 4a7c153a2666..95a51c2efa63 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c

@@ -2263,6 +2263,7 @@ mvneta_swbm_rx_frame(struct mvneta_port *pp,
 	prefetch(data);
 	xdp_prepare_buff(xdp, data, pp->rx_offset_correction + MVNETA_MH_SIZE,
 			 data_len, false);
+	xdp->flags = mvneta_rx_csum(pp, rx_desc->status);
 
 	sinfo = xdp_get_shared_info_from_buff(xdp);
 	sinfo->nr_frags = 0;

@@ -2317,7 +2318,7 @@ mvneta_swbm_add_rx_fragment(struct mvneta_port *pp,
 
 static struct sk_buff *
 mvneta_swbm_build_skb(struct mvneta_port *pp, struct mvneta_rx_queue *rxq,
-		      struct xdp_buff *xdp, u32 desc_status)
+		      struct xdp_buff *xdp)
 {
 	struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
 	int i, num_frags = sinfo->nr_frags;

@@ -2331,7 +2332,7 @@ mvneta_swbm_build_skb(struct mvneta_port *pp, struct mvneta_rx_queue *rxq,
 
 	skb_reserve(skb, xdp->data - xdp->data_hard_start);
 	skb_put(skb, xdp->data_end - xdp->data);
-	skb->ip_summed = mvneta_rx_csum(pp, desc_status);
+	xdp_buff_get_csum(xdp, skb);
 
 	for (i = 0; i < num_frags; i++) {
 		skb_frag_t *frag = &sinfo->frags[i];

@@ -2355,8 +2356,8 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
 	struct skb_shared_info sinfo;
 	struct mvneta_stats ps = {};
 	struct bpf_prog *xdp_prog;
-	u32 desc_status, frame_sz;
 	struct xdp_buff xdp_buf;
+	u32 frame_sz;
 
 	xdp_init_buff(&xdp_buf, PAGE_SIZE, &rxq->xdp_rxq);
 	xdp_buf.data_hard_start = NULL;

@@ -2392,7 +2393,6 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
 
 			size = rx_desc->data_size;
 			frame_sz = size - ETH_FCS_LEN;
-			desc_status = rx_status;
 
 			mvneta_swbm_rx_frame(pp, rx_desc, rxq, &xdp_buf,
 					     &size, page);

@@ -2421,7 +2421,7 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
 		    mvneta_run_xdp(pp, rxq, xdp_prog, &xdp_buf, frame_sz, &ps))
 			goto next;
 
-		skb = mvneta_swbm_build_skb(pp, rxq, &xdp_buf, desc_status);
+		skb = mvneta_swbm_build_skb(pp, rxq, &xdp_buf);
 		if (IS_ERR(skb)) {
 			struct mvneta_pcpu_stats *stats = this_cpu_ptr(pp->stats);

-- 
2.31.1

[RFC bpf-next 4/4] net: xdp: update csum building the skb

From: Lorenzo Bianconi <lorenzo@kernel.org>
Date: 2021-05-28 17:44:25

update skb->ip_summed and skb->csum filed building the skb in
__xdp_build_skb_from_frame routine

Co-developed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 net/core/xdp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/xdp.c b/net/core/xdp.c
index 725d20f1b100..aadcbbc438c3 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c

@@ -555,10 +555,10 @@ struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame *xdpf,
 	skb->protocol = eth_type_trans(skb, dev);
 
 	/* Optional SKB info, currently missing:
-	 * - HW checksum info		(skb->ip_summed)
 	 * - HW RX hash			(skb_set_hash)
 	 * - RX ring dev queue index	(skb_record_rx_queue)
 	 */
+	xdp_frame_get_csum(xdpf, skb);
 
 	/* Until page_pool get SKB return path, release DMA here */
 	xdp_release_frame(xdpf);

-- 
2.31.1

Re: [RFC bpf-next 0/4] add partial rx hw csum offload support for XDP

From: David Ahern <hidden>
Date: 2021-05-28 18:01:24

On 5/28/21 11:43 AM, Lorenzo Bianconi wrote:

Enable xdp rx checksum offload support for CHECKSUM_UNNECESSARY use-case.
Introduce flag field in xdp_buff/xdp_frame in order to save the checksum
result from the NIC and have a fast access to it performing XDP_REDIRECT.
CHECKSUM_COMPLETE is not supported yet since it will require adding the
csum result to the xdp_metadata area.
Moreover flag field will be reused for xdp multi-buff support.
This series has been tested generating UDP traffic with pktgen and performing
a xdp_redirect from an ixgbe device to a remote CPUMAP entry. PPS results show
a negligible penalty respect to the baseline where the UDP checksum has been
disabled. More info about the test can be found here [0].

[0] https://github.com/xdp-project/xdp-project/blob/master/areas/core/xdp_frame01_checksum.org

For the wider audience, another example of the performance benefit of
this rather simple change is XDP_REDIRECT to VMs (and containers) for
TCP traffic which requires checksum.

The VM piece requires the change to the tun driver from my original
patch which passes the VIRTIO_NET_HDR_F_DATA_VALID flag for
CHECKSUM_UNNECESSARY:

https://github.com/dsahern/linux/commit/b6b4d4ef9562383d8b407a873d30082afdc1b89c

(I can send that followup after this set lands.)

Using ConnectX-5 and the mlx5 change in the above commit I was seeing at
least a 300k pps improvement depending on the test. e.g., from 2M pps to
2.3M for 1500 MTU packets or 1.3M to 1.6M for 3400 MTU.

Similar results for containers.

Right now the checksum validation done by H/W is lost on the redirect.
This change propagates the validation and avoids the csum_partial
overhead as the skb is processed.

Re: [RFC bpf-next 1/4] net: xdp: introduce flags field in xdp_buff and xdp_frame

From: Tom Herbert <hidden>
Date: 2021-05-28 21:18:48

On Fri, May 28, 2021 at 10:44 AM Lorenzo Bianconi [off-list ref] wrote:

Introduce flag field in xdp_buff and xdp_frame data structure in order
to report xdp_buffer metadata. For the moment just hw checksum hints
are defined but flags field will be reused for xdp multi-buffer
For the moment just CHECKSUM_UNNECESSARY is supported.
CHECKSUM_COMPLETE will need to set csum value in metada space.

Lorenzo,

This isn't sufficient for the checksum-unnecessary interface, we'd
also need ability to set csum_level for cases the device validated
more than one checksum.

IMO, we shouldn't support CHECKSUM_UNNECESSARY for new uses like this.
For years now, the Linux community has been pleading with vendors to
provide CHECKSUM_COMPLETE which is far more useful and robust than
CHECSUM_UNNECESSARY, and yet some still haven't got with the program
even though we see more and more instances where CHECKSUM_UNNECESSARY
doesn't even work at all (e.g. cases with SRv6, new encaps device
doesn't understand). I believe it's time to take a stand! :-)

Tom

quoted hunk

Signed-off-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 include/net/xdp.h | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/include/net/xdp.h b/include/net/xdp.h
index 5533f0ab2afc..e81ac505752b 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h

@@ -66,6 +66,13 @@ struct xdp_txq_info {
        struct net_device *dev;
 };

+/* xdp metadata bitmask */
+#define XDP_CSUM_MASK          GENMASK(1, 0)
+enum xdp_flags {
+       XDP_CSUM_UNNECESSARY    = BIT(0),
+       XDP_CSUM_COMPLETE       = BIT(1),
+};
+
 struct xdp_buff {
        void *data;
        void *data_end;

@@ -74,6 +81,7 @@ struct xdp_buff {
        struct xdp_rxq_info *rxq;
        struct xdp_txq_info *txq;
        u32 frame_sz; /* frame size to deduce data_hard_end/reserved tailroom*/
+       u16 flags; /* xdp_flags */
 };

 static __always_inline void

@@ -81,6 +89,7 @@ xdp_init_buff(struct xdp_buff *xdp, u32 frame_sz, struct xdp_rxq_info *rxq)
 {
        xdp->frame_sz = frame_sz;
        xdp->rxq = rxq;
+       xdp->flags = 0;
 }

 static __always_inline void

@@ -95,6 +104,18 @@ xdp_prepare_buff(struct xdp_buff *xdp, unsigned char *hard_start,
        xdp->data_meta = meta_valid ? data : data + 1;
 }

+static __always_inline void
+xdp_buff_get_csum(struct xdp_buff *xdp, struct sk_buff *skb)
+{
+       switch (xdp->flags & XDP_CSUM_MASK) {
+       case XDP_CSUM_UNNECESSARY:
+               skb->ip_summed = CHECKSUM_UNNECESSARY;
+               break;
+       default:
+               break;
+       }
+}
+
 /* Reserve memory area at end-of data area.
  *
  * This macro reserves tailroom in the XDP buffer by limiting the

@@ -122,8 +143,21 @@ struct xdp_frame {
         */
        struct xdp_mem_info mem;
        struct net_device *dev_rx; /* used by cpumap */
+       u16 flags; /* xdp_flags */
 };

+static __always_inline void
+xdp_frame_get_csum(struct xdp_frame *xdpf, struct sk_buff *skb)
+{
+       switch (xdpf->flags & XDP_CSUM_MASK) {
+       case XDP_CSUM_UNNECESSARY:
+               skb->ip_summed = CHECKSUM_UNNECESSARY;
+               break;
+       default:
+               break;
+       }
+}
+
 #define XDP_BULK_QUEUE_SIZE    16
 struct xdp_frame_bulk {
        int count;

@@ -180,6 +214,7 @@ void xdp_convert_frame_to_buff(struct xdp_frame *frame, struct xdp_buff *xdp)
        xdp->data_end = frame->data + frame->len;
        xdp->data_meta = frame->data - frame->metasize;
        xdp->frame_sz = frame->frame_sz;
+       xdp->flags = frame->flags;
 }

 static inline

@@ -206,6 +241,7 @@ int xdp_update_frame_from_buff(struct xdp_buff *xdp,
        xdp_frame->headroom = headroom - sizeof(*xdp_frame);
        xdp_frame->metasize = metasize;
        xdp_frame->frame_sz = xdp->frame_sz;
+       xdp_frame->flags = xdp->flags;

        return 0;
 }
--

2.31.1

Re: [RFC bpf-next 1/4] net: xdp: introduce flags field in xdp_buff and xdp_frame

From: David Ahern <hidden>
Date: 2021-05-29 01:33:25

On 5/28/21 3:18 PM, Tom Herbert wrote:

On Fri, May 28, 2021 at 10:44 AM Lorenzo Bianconi [off-list ref] wrote:

quoted

Introduce flag field in xdp_buff and xdp_frame data structure in order
to report xdp_buffer metadata. For the moment just hw checksum hints
are defined but flags field will be reused for xdp multi-buffer
For the moment just CHECKSUM_UNNECESSARY is supported.
CHECKSUM_COMPLETE will need to set csum value in metada space.

Lorenzo,

This isn't sufficient for the checksum-unnecessary interface, we'd
also need ability to set csum_level for cases the device validated
more than one checksum.

That's on me. The original patch was for XDP_REDIRECT to VMs and the
VIRTIO_NET_HDR_ API does not support csum_level.
VIRTIO_NET_HDR_F_DATA_VALID means CHECKSUM_UNNECESSARY, an API
implemented 10 years ago.

IMO, we shouldn't support CHECKSUM_UNNECESSARY for new uses like this.
For years now, the Linux community has been pleading with vendors to
provide CHECKSUM_COMPLETE which is far more useful and robust than
CHECSUM_UNNECESSARY, and yet some still haven't got with the program
even though we see more and more instances where CHECKSUM_UNNECESSARY
doesn't even work at all (e.g. cases with SRv6, new encaps device
doesn't understand). I believe it's time to take a stand! :-)

There is no new hardware or new feature at play here. This about XDP
frames getting the checksum validation setting that an skb enjoys today.
You are taking a stand against S/W equivalency with the existing NICs?
That basically penalizes XDP, continuing to limit its usefulness with
very well established use cases that could benefit from it.

Re: [RFC bpf-next 1/4] net: xdp: introduce flags field in xdp_buff and xdp_frame

From: Jakub Kicinski <kuba@kernel.org>
Date: 2021-05-29 04:56:58

On Fri, 28 May 2021 14:18:33 -0700 Tom Herbert wrote:

On Fri, May 28, 2021 at 10:44 AM Lorenzo Bianconi [off-list ref] wrote:

quoted

Introduce flag field in xdp_buff and xdp_frame data structure in order
to report xdp_buffer metadata. For the moment just hw checksum hints
are defined but flags field will be reused for xdp multi-buffer
For the moment just CHECKSUM_UNNECESSARY is supported.
CHECKSUM_COMPLETE will need to set csum value in metada space.

Lorenzo,

This isn't sufficient for the checksum-unnecessary interface, we'd
also need ability to set csum_level for cases the device validated
more than one checksum.

IMO, we shouldn't support CHECKSUM_UNNECESSARY for new uses like this.
For years now, the Linux community has been pleading with vendors to
provide CHECKSUM_COMPLETE which is far more useful and robust than
CHECSUM_UNNECESSARY, and yet some still haven't got with the program
even though we see more and more instances where CHECKSUM_UNNECESSARY
doesn't even work at all (e.g. cases with SRv6, new encaps device
doesn't understand). I believe it's time to take a stand! :-)

I must agree. Not supporting CHECKSUM_COMPLETE seems like a step back.

Re: [RFC bpf-next 1/4] net: xdp: introduce flags field in xdp_buff and xdp_frame

From: Lorenzo Bianconi <lorenzo@kernel.org>
Date: 2021-05-29 13:34:26

On Fri, May 28, 2021 at 10:44 AM Lorenzo Bianconi [off-list ref] wrote:

quoted

Introduce flag field in xdp_buff and xdp_frame data structure in order
to report xdp_buffer metadata. For the moment just hw checksum hints
are defined but flags field will be reused for xdp multi-buffer
For the moment just CHECKSUM_UNNECESSARY is supported.
CHECKSUM_COMPLETE will need to set csum value in metada space.

Lorenzo,

Hi Tom,

This isn't sufficient for the checksum-unnecessary interface, we'd
also need ability to set csum_level for cases the device validated
more than one checksum.

ack, right. I guess we can put this info in xdp metadata or do you think we can
add it in xdp_buff/xdp_frame as well?

IMO, we shouldn't support CHECKSUM_UNNECESSARY for new uses like this.
For years now, the Linux community has been pleading with vendors to
provide CHECKSUM_COMPLETE which is far more useful and robust than
CHECSUM_UNNECESSARY, and yet some still haven't got with the program
even though we see more and more instances where CHECKSUM_UNNECESSARY
doesn't even work at all (e.g. cases with SRv6, new encaps device
doesn't understand). I believe it's time to take a stand! :-)

I completely agree CHECKSUM_COMPLETE is more useful and robust than
CHECSUM_UNNECESSARY and I want to add support for it as soon as we
agree on the best way to do it. At the same time there are plenty of
XDP NICs where this feature is quite useful since they support just
CHECSUM_UNNECESSARY.

Regards,
Lorenzo

Tom

quoted

Signed-off-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 include/net/xdp.h | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/include/net/xdp.h b/include/net/xdp.h
index 5533f0ab2afc..e81ac505752b 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h

@@ -66,6 +66,13 @@ struct xdp_txq_info {
        struct net_device *dev;
 };

+/* xdp metadata bitmask */
+#define XDP_CSUM_MASK          GENMASK(1, 0)
+enum xdp_flags {
+       XDP_CSUM_UNNECESSARY    = BIT(0),
+       XDP_CSUM_COMPLETE       = BIT(1),
+};
+
 struct xdp_buff {
        void *data;
        void *data_end;

@@ -74,6 +81,7 @@ struct xdp_buff {
        struct xdp_rxq_info *rxq;
        struct xdp_txq_info *txq;
        u32 frame_sz; /* frame size to deduce data_hard_end/reserved tailroom*/
+       u16 flags; /* xdp_flags */
 };

 static __always_inline void

@@ -81,6 +89,7 @@ xdp_init_buff(struct xdp_buff *xdp, u32 frame_sz, struct xdp_rxq_info *rxq)
 {
        xdp->frame_sz = frame_sz;
        xdp->rxq = rxq;
+       xdp->flags = 0;
 }

 static __always_inline void

@@ -95,6 +104,18 @@ xdp_prepare_buff(struct xdp_buff *xdp, unsigned char *hard_start,
        xdp->data_meta = meta_valid ? data : data + 1;
 }

+static __always_inline void
+xdp_buff_get_csum(struct xdp_buff *xdp, struct sk_buff *skb)
+{
+       switch (xdp->flags & XDP_CSUM_MASK) {
+       case XDP_CSUM_UNNECESSARY:
+               skb->ip_summed = CHECKSUM_UNNECESSARY;
+               break;
+       default:
+               break;
+       }
+}
+
 /* Reserve memory area at end-of data area.
  *
  * This macro reserves tailroom in the XDP buffer by limiting the

@@ -122,8 +143,21 @@ struct xdp_frame {
         */
        struct xdp_mem_info mem;
        struct net_device *dev_rx; /* used by cpumap */
+       u16 flags; /* xdp_flags */
 };

+static __always_inline void
+xdp_frame_get_csum(struct xdp_frame *xdpf, struct sk_buff *skb)
+{
+       switch (xdpf->flags & XDP_CSUM_MASK) {
+       case XDP_CSUM_UNNECESSARY:
+               skb->ip_summed = CHECKSUM_UNNECESSARY;
+               break;
+       default:
+               break;
+       }
+}
+
 #define XDP_BULK_QUEUE_SIZE    16
 struct xdp_frame_bulk {
        int count;

@@ -180,6 +214,7 @@ void xdp_convert_frame_to_buff(struct xdp_frame *frame, struct xdp_buff *xdp)
        xdp->data_end = frame->data + frame->len;
        xdp->data_meta = frame->data - frame->metasize;
        xdp->frame_sz = frame->frame_sz;
+       xdp->flags = frame->flags;
 }

 static inline

@@ -206,6 +241,7 @@ int xdp_update_frame_from_buff(struct xdp_buff *xdp,
        xdp_frame->headroom = headroom - sizeof(*xdp_frame);
        xdp_frame->metasize = metasize;
        xdp_frame->frame_sz = xdp->frame_sz;
+       xdp_frame->flags = xdp->flags;

        return 0;
 }
--

2.31.1

Re: [RFC bpf-next 1/4] net: xdp: introduce flags field in xdp_buff and xdp_frame

From: Lorenzo Bianconi <lorenzo@kernel.org>
Date: 2021-05-29 13:37:35

On Fri, 28 May 2021 14:18:33 -0700 Tom Herbert wrote:

quoted

On Fri, May 28, 2021 at 10:44 AM Lorenzo Bianconi [off-list ref] wrote:

quoted

Introduce flag field in xdp_buff and xdp_frame data structure in order
to report xdp_buffer metadata. For the moment just hw checksum hints
are defined but flags field will be reused for xdp multi-buffer
For the moment just CHECKSUM_UNNECESSARY is supported.
CHECKSUM_COMPLETE will need to set csum value in metada space.

Lorenzo,

This isn't sufficient for the checksum-unnecessary interface, we'd
also need ability to set csum_level for cases the device validated
more than one checksum.

IMO, we shouldn't support CHECKSUM_UNNECESSARY for new uses like this.
For years now, the Linux community has been pleading with vendors to
provide CHECKSUM_COMPLETE which is far more useful and robust than
CHECSUM_UNNECESSARY, and yet some still haven't got with the program
even though we see more and more instances where CHECKSUM_UNNECESSARY
doesn't even work at all (e.g. cases with SRv6, new encaps device
doesn't understand). I believe it's time to take a stand! :-)

I must agree. Not supporting CHECKSUM_COMPLETE seems like a step back.

I completely agree on it and I want add support for CHECKSUM_COMPLETE as soon
as we decide what is the best way to store csum value (xdp_metadata?). At the
same time this preliminary series wants to add support just for
CHECSUM_UNNECESSARY. Moreover the flags field in xdp_buff/xdp_frame will be
reused for xdp multi-buff work.

Regards,
Lorenzo

Re: [RFC bpf-next 1/4] net: xdp: introduce flags field in xdp_buff and xdp_frame

From: Jesper Dangaard Brouer <hidden>
Date: 2021-05-31 11:07:38

On Sat, 29 May 2021 15:34:18 +0200
Lorenzo Bianconi [off-list ref] wrote:

quoted

On Fri, May 28, 2021 at 10:44 AM Lorenzo Bianconi [off-list ref] wrote:

quoted

Introduce flag field in xdp_buff and xdp_frame data structure in order
to report xdp_buffer metadata. For the moment just hw checksum hints
are defined but flags field will be reused for xdp multi-buffer
For the moment just CHECKSUM_UNNECESSARY is supported.
CHECKSUM_COMPLETE will need to set csum value in metada space.

Lorenzo,

Hi Tom,

quoted

This isn't sufficient for the checksum-unnecessary interface, we'd
also need ability to set csum_level for cases the device validated
more than one checksum.

ack, right. I guess we can put this info in xdp metadata or do you
think we can add it in xdp_buff/xdp_frame as well?

This is an interesting question as where do we draw the line.  I
definitely only don't want to add the same information in two places.

As is clear by the XDP-hints discussion: Today we are lacking *kernel*
infrastructure to interpret the XDP-metadata area when we create the
SKB from xdp_frame.  I want to add this capability...

(See XDP-hints discussion, as wisely pointed out by John, the BPF-prog
infrastructure to interpret XDP-metadata via BTF-info is already
available to userspace loading BPF-progs, but AFAIK the kernel is
lacking this capability. Maybe we will end-up loading BPF-progs that
populate SKB fields based on xdp_frame + XDP-metadata area... I'm
keeping an open mind for the solutions in this space.).

The question is really, should we wait for this infra (that can use
csum value from metadata) or should be go ahead and expand
xdp_buff/xdp_frame with an csum value (+ ip_summed) for the
CHECKSUM_COMPLETE use-case?

quoted

IMO, we shouldn't support CHECKSUM_UNNECESSARY for new uses like this.
For years now, the Linux community has been pleading with vendors to
provide CHECKSUM_COMPLETE which is far more useful and robust than
CHECSUM_UNNECESSARY, and yet some still haven't got with the program
even though we see more and more instances where CHECKSUM_UNNECESSARY
doesn't even work at all (e.g. cases with SRv6, new encaps device
doesn't understand). I believe it's time to take a stand! :-)

I completely agree CHECKSUM_COMPLETE is more useful and robust than
CHECSUM_UNNECESSARY and I want to add support for it as soon as we
agree on the best way to do it. At the same time there are plenty of
XDP NICs where this feature is quite useful since they support just
CHECSUM_UNNECESSARY.

Regards,
Lorenzo

quoted

Tom

quoted

Signed-off-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 include/net/xdp.h | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/include/net/xdp.h b/include/net/xdp.h
index 5533f0ab2afc..e81ac505752b 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h

@@ -66,6 +66,13 @@ struct xdp_txq_info {
        struct net_device *dev;
 };

+/* xdp metadata bitmask */
+#define XDP_CSUM_MASK          GENMASK(1, 0)
+enum xdp_flags {
+       XDP_CSUM_UNNECESSARY    = BIT(0),
+       XDP_CSUM_COMPLETE       = BIT(1),
+};
+
 struct xdp_buff {
        void *data;
        void *data_end;

@@ -74,6 +81,7 @@ struct xdp_buff {
        struct xdp_rxq_info *rxq;
        struct xdp_txq_info *txq;
        u32 frame_sz; /* frame size to deduce data_hard_end/reserved tailroom*/
+       u16 flags; /* xdp_flags */
 };

 static __always_inline void

@@ -81,6 +89,7 @@ xdp_init_buff(struct xdp_buff *xdp, u32 frame_sz, struct xdp_rxq_info *rxq)
 {
        xdp->frame_sz = frame_sz;
        xdp->rxq = rxq;
+       xdp->flags = 0;
 }

 static __always_inline void

@@ -95,6 +104,18 @@ xdp_prepare_buff(struct xdp_buff *xdp, unsigned char *hard_start,
        xdp->data_meta = meta_valid ? data : data + 1;
 }

+static __always_inline void
+xdp_buff_get_csum(struct xdp_buff *xdp, struct sk_buff *skb)
+{
+       switch (xdp->flags & XDP_CSUM_MASK) {
+       case XDP_CSUM_UNNECESSARY:
+               skb->ip_summed = CHECKSUM_UNNECESSARY;
+               break;
+       default:
+               break;
+       }
+}
+
 /* Reserve memory area at end-of data area.
  *
  * This macro reserves tailroom in the XDP buffer by limiting the

@@ -122,8 +143,21 @@ struct xdp_frame {
         */
        struct xdp_mem_info mem;
        struct net_device *dev_rx; /* used by cpumap */
+       u16 flags; /* xdp_flags */
 };

+static __always_inline void
+xdp_frame_get_csum(struct xdp_frame *xdpf, struct sk_buff *skb)
+{
+       switch (xdpf->flags & XDP_CSUM_MASK) {
+       case XDP_CSUM_UNNECESSARY:
+               skb->ip_summed = CHECKSUM_UNNECESSARY;
+               break;
+       default:
+               break;
+       }
+}
+
 #define XDP_BULK_QUEUE_SIZE    16
 struct xdp_frame_bulk {
        int count;

@@ -180,6 +214,7 @@ void xdp_convert_frame_to_buff(struct xdp_frame *frame, struct xdp_buff *xdp)
        xdp->data_end = frame->data + frame->len;
        xdp->data_meta = frame->data - frame->metasize;
        xdp->frame_sz = frame->frame_sz;
+       xdp->flags = frame->flags;
 }

 static inline

@@ -206,6 +241,7 @@ int xdp_update_frame_from_buff(struct xdp_buff *xdp,
        xdp_frame->headroom = headroom - sizeof(*xdp_frame);
        xdp_frame->metasize = metasize;
        xdp_frame->frame_sz = xdp->frame_sz;
+       xdp_frame->flags = xdp->flags;

        return 0;
 }
--

2.31.1



-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

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