net/mlx5e: Add XSK zero-copy support

This commit adds support for AF_XDP zero-copy RX and TX.

We create a dedicated XSK RQ inside the channel, it means that two
RQs are running simultaneously: one for non-XSK traffic and the other
for XSK traffic. The regular and XSK RQs use a single ID namespace split
into two halves: the lower half is regular RQs, and the upper half is
XSK RQs. When any zero-copy AF_XDP socket is active, changing the number
of channels is not allowed, because it would break to mapping between
XSK RQ IDs and channels.

XSK requires different page allocation and release routines. Such
functions as mlx5e_{alloc,free}_rx_mpwqe and mlx5e_{get,put}_rx_frag are
generic enough to be used for both regular and XSK RQs, and they use the
mlx5e_page_{alloc,release} wrappers around the real allocation
functions. Function pointers are not used to avoid losing the
performance with retpolines. Wherever it's certain that the regular
(non-XSK) page release function should be used, it's called directly.

Only the stats that could be meaningful for XSK are exposed to the
userspace. Those that don't take part in the XSK flow are not
considered.

Note that we don't wait for WQEs on the XSK RQ (unlike the regular RQ),
because the newer xdpsock sample doesn't provide any Fill Ring entries
at the setup stage.

We create a dedicated XSK SQ in the channel. This separation has its
advantages:

1. When the UMEM is closed, the XSK SQ can also be closed and stop
receiving completions. If an existing SQ was used for XSK, it would
continue receiving completions for the packets of the closed socket. If
a new UMEM was opened at that point, it would start getting completions
that don't belong to it.

2. Calculating statistics separately.

When the userspace kicks the TX, the driver triggers a hardware
interrupt by posting a NOP to a dedicated XSK ICO (internal control
operations) SQ, in order to trigger NAPI on the right CPU core. This XSK
ICO SQ is protected by a spinlock, as the userspace application may kick
the TX from any core.

Store the pointers to the UMEMs in the net device private context,
independently from the kernel. This way the driver can distinguish
between the zero-copy and non-zero-copy UMEMs. The kernel function
xdp_get_umem_from_qid does not care about this difference, but the
driver is only interested in zero-copy UMEMs, particularly, on the
cleanup it determines whether to close the XSK RQ and SQ or not by
looking at the presence of the UMEM. Use state_lock to protect the
access to this area of UMEM pointers.

LRO isn't compatible with XDP, but there may be active UMEMs while
XDP is off. If this is the case, don't allow LRO to ensure XDP can
be reenabled at any time.

The validation of XSK parameters typically happens when XSK queues
open. However, when the interface is down or the XDP program isn't
set, it's still possible to have active AF_XDP sockets and even to
open new, but the XSK queues will be closed. To cover these cases,
perform the validation also in these flows:

1. A new UMEM is registered, but the XSK queues aren't going to be
created due to missing XDP program or interface being down.

2. MTU changes while there are UMEMs registered.

Having this early check prevents mlx5e_open_channels from failing
at a later stage, where recovery is impossible and the application
has no chance to handle the error, because it got the successful
return value for an MTU change or XSK open operation.

The performance testing was performed on a machine with the following
configuration:

- 24 cores of Intel Xeon E5-2620 v3 @ 2.40 GHz
- Mellanox ConnectX-5 Ex with 100 Gbit/s link

The results with retpoline disabled, single stream:

txonly: 33.3 Mpps (21.5 Mpps with queue and app pinned to the same CPU)
rxdrop: 12.2 Mpps
l2fwd: 9.4 Mpps

The results with retpoline enabled, single stream:

txonly: 21.3 Mpps (14.1 Mpps with queue and app pinned to the same CPU)
rxdrop: 9.9 Mpps
l2fwd: 6.8 Mpps

Signed-off-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Acked-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 192 insertions, 0 deletions

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.c
new file mode 100644
index 000000000000..6a55573ec8f2
--- /dev/null
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.c
@@ -0,0 +1,192 @@
+// SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB
+/* Copyright (c) 2019 Mellanox Technologies. */
+
+#include "rx.h"
+#include "en/xdp.h"
+#include <net/xdp_sock.h>
+
+/* RX data path */
+
+bool mlx5e_xsk_pages_enough_umem(struct mlx5e_rq *rq, int count)
+{
+	/* Check in advance that we have enough frames, instead of allocating
+	 * one-by-one, failing and moving frames to the Reuse Ring.
+	 */
+	return xsk_umem_has_addrs_rq(rq->umem, count);
+}
+
+int mlx5e_xsk_page_alloc_umem(struct mlx5e_rq *rq,
+			      struct mlx5e_dma_info *dma_info)
+{
+	struct xdp_umem *umem = rq->umem;
+	u64 handle;
+
+	if (!xsk_umem_peek_addr_rq(umem, &handle))
+		return -ENOMEM;
+
+	dma_info->xsk.handle = handle + rq->buff.umem_headroom;
+	dma_info->xsk.data = xdp_umem_get_data(umem, dma_info->xsk.handle);
+
+	/* No need to add headroom to the DMA address. In striding RQ case, we
+	 * just provide pages for UMR, and headroom is counted at the setup
+	 * stage when creating a WQE. In non-striding RQ case, headroom is
+	 * accounted in mlx5e_alloc_rx_wqe.
+	 */
+	dma_info->addr = xdp_umem_get_dma(umem, handle);
+
+	xsk_umem_discard_addr_rq(umem);
+
+	dma_sync_single_for_device(rq->pdev, dma_info->addr, PAGE_SIZE,
+				   DMA_BIDIRECTIONAL);
+
+	return 0;
+}
+
+static inline void mlx5e_xsk_recycle_frame(struct mlx5e_rq *rq, u64 handle)
+{
+	xsk_umem_fq_reuse(rq->umem, handle & rq->umem->chunk_mask);
+}
+
+/* XSKRQ uses pages from UMEM, they must not be released. They are returned to
+ * the userspace if possible, and if not, this function is called to reuse them
+ * in the driver.
+ */
+void mlx5e_xsk_page_release(struct mlx5e_rq *rq,
+			    struct mlx5e_dma_info *dma_info)
+{
+	mlx5e_xsk_recycle_frame(rq, dma_info->xsk.handle);
+}
+
+/* Return a frame back to the hardware to fill in again. It is used by XDP when
+ * the XDP program returns XDP_TX or XDP_REDIRECT not to an XSKMAP.
+ */
+void mlx5e_xsk_zca_free(struct zero_copy_allocator *zca, unsigned long handle)
+{
+	struct mlx5e_rq *rq = container_of(zca, struct mlx5e_rq, zca);
+
+	mlx5e_xsk_recycle_frame(rq, handle);
+}
+
+static struct sk_buff *mlx5e_xsk_construct_skb(struct mlx5e_rq *rq, void *data,
+					       u32 cqe_bcnt)
+{
+	struct sk_buff *skb;
+
+	skb = napi_alloc_skb(rq->cq.napi, cqe_bcnt);
+	if (unlikely(!skb)) {
+		rq->stats->buff_alloc_err++;
+		return NULL;
+	}
+
+	skb_put_data(skb, data, cqe_bcnt);
+
+	return skb;
+}
+
+struct sk_buff *mlx5e_xsk_skb_from_cqe_mpwrq_linear(struct mlx5e_rq *rq,
+						    struct mlx5e_mpw_info *wi,
+						    u16 cqe_bcnt,
+						    u32 head_offset,
+						    u32 page_idx)
+{
+	struct mlx5e_dma_info *di = &wi->umr.dma_info[page_idx];
+	u16 rx_headroom = rq->buff.headroom - rq->buff.umem_headroom;
+	u32 cqe_bcnt32 = cqe_bcnt;
+	void *va, *data;
+	u32 frag_size;
+	bool consumed;
+
+	/* Check packet size. Note LRO doesn't use linear SKB */
+	if (unlikely(cqe_bcnt > rq->hw_mtu)) {
+		rq->stats->oversize_pkts_sw_drop++;
+		return NULL;
+	}
+
+	/* head_offset is not used in this function, because di->xsk.data and
+	 * di->addr point directly to the necessary place. Furthermore, in the
+	 * current implementation, one page = one packet = one frame, so
+	 * head_offset should always be 0.
+	 */
+	WARN_ON_ONCE(head_offset);
+
+	va             = di->xsk.data;
+	data           = va + rx_headroom;
+	frag_size      = rq->buff.headroom + cqe_bcnt32;
+
+	dma_sync_single_for_cpu(rq->pdev, di->addr, frag_size, DMA_BIDIRECTIONAL);
+	prefetch(data);
+
+	rcu_read_lock();
+	consumed = mlx5e_xdp_handle(rq, di, va, &rx_headroom, &cqe_bcnt32, true);
+	rcu_read_unlock();
+
+	/* Possible flows:
+	 * - XDP_REDIRECT to XSKMAP:
+	 *   The page is owned by the userspace from now.
+	 * - XDP_TX and other XDP_REDIRECTs:
+	 *   The page was returned by ZCA and recycled.
+	 * - XDP_DROP:
+	 *   Recycle the page.
+	 * - XDP_PASS:
+	 *   Allocate an SKB, copy the data and recycle the page.
+	 *
+	 * Pages to be recycled go to the Reuse Ring on MPWQE deallocation. Its
+	 * size is the same as the Driver RX Ring's size, and pages for WQEs are
+	 * allocated first from the Reuse Ring, so it has enough space.
+	 */
+
+	if (likely(consumed)) {
+		if (likely(__test_and_clear_bit(MLX5E_RQ_FLAG_XDP_XMIT, rq->flags)))
+			__set_bit(page_idx, wi->xdp_xmit_bitmap); /* non-atomic */
+		return NULL; /* page/packet was consumed by XDP */
+	}
+
+	/* XDP_PASS: copy the data from the UMEM to a new SKB and reuse the
+	 * frame. On SKB allocation failure, NULL is returned.
+	 */
+	return mlx5e_xsk_construct_skb(rq, data, cqe_bcnt32);
+}
+
+struct sk_buff *mlx5e_xsk_skb_from_cqe_linear(struct mlx5e_rq *rq,
+					      struct mlx5_cqe64 *cqe,
+					      struct mlx5e_wqe_frag_info *wi,
+					      u32 cqe_bcnt)
+{
+	struct mlx5e_dma_info *di = wi->di;
+	u16 rx_headroom = rq->buff.headroom - rq->buff.umem_headroom;
+	void *va, *data;
+	bool consumed;
+	u32 frag_size;
+
+	/* wi->offset is not used in this function, because di->xsk.data and
+	 * di->addr point directly to the necessary place. Furthermore, in the
+	 * current implementation, one page = one packet = one frame, so
+	 * wi->offset should always be 0.
+	 */
+	WARN_ON_ONCE(wi->offset);
+
+	va             = di->xsk.data;
+	data           = va + rx_headroom;
+	frag_size      = rq->buff.headroom + cqe_bcnt;
+
+	dma_sync_single_for_cpu(rq->pdev, di->addr, frag_size, DMA_BIDIRECTIONAL);
+	prefetch(data);
+
+	if (unlikely(get_cqe_opcode(cqe) != MLX5_CQE_RESP_SEND)) {
+		rq->stats->wqe_err++;
+		return NULL;
+	}
+
+	rcu_read_lock();
+	consumed = mlx5e_xdp_handle(rq, di, va, &rx_headroom, &cqe_bcnt, true);
+	rcu_read_unlock();
+
+	if (likely(consumed))
+		return NULL; /* page/packet was consumed by XDP */
+
+	/* XDP_PASS: copy the data from the UMEM to a new SKB. The frame reuse
+	 * will be handled by mlx5e_put_rx_frag.
+	 * On SKB allocation failure, NULL is returned.
+	 */
+	return mlx5e_xsk_construct_skb(rq, data, cqe_bcnt);
+}