xsk: Introduce AF_XDP buffer allocation API

In order to simplify AF_XDP zero-copy enablement for NIC driver
developers, a new AF_XDP buffer allocation API is added. The
implementation is based on a single core (single producer/consumer)
buffer pool for the AF_XDP UMEM.

A buffer is allocated using the xsk_buff_alloc() function, and
returned using xsk_buff_free(). If a buffer is disassociated with the
pool, e.g. when a buffer is passed to an AF_XDP socket, a buffer is
said to be released. Currently, the release function is only used by
the AF_XDP internals and not visible to the driver.

Drivers using this API should register the XDP memory model with the
new MEM_TYPE_XSK_BUFF_POOL type.

The API is defined in net/xdp_sock_drv.h.

The buffer type is struct xdp_buff, and follows the lifetime of
regular xdp_buffs, i.e.  the lifetime of an xdp_buff is restricted to
a NAPI context. In other words, the API is not replacing xdp_frames.

In addition to introducing the API and implementations, the AF_XDP
core is migrated to use the new APIs.

rfc->v1: Fixed build errors/warnings for m68k and riscv. (kbuild test
         robot)
         Added headroom/chunk size getter. (Maxim/Björn)

v1->v2: Swapped SoBs. (Maxim)

v2->v3: Initialize struct xdp_buff member frame_sz. (Björn)
        Add API to query the DMA address of a frame. (Maxim)
        Do DMA sync for CPU till the end of the frame to handle
        possible growth (frame_sz). (Maxim)

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200520192103.355233-6-bjorn.topel@gmail.com

include/net/xdp.h

@@ -40,6 +40,7 @@ enum xdp_mem_type {
 	MEM_TYPE_PAGE_ORDER0,     /* Orig XDP full page model */
 	MEM_TYPE_PAGE_POOL,
 	MEM_TYPE_ZERO_COPY,
+	MEM_TYPE_XSK_BUFF_POOL,
 	MEM_TYPE_MAX,
 };
 
@@ -119,7 +120,8 @@ struct xdp_frame *convert_to_xdp_frame(struct xdp_buff *xdp)
 	int metasize;
 	int headroom;
 
-	if (xdp->rxq->mem.type == MEM_TYPE_ZERO_COPY)
+	if (xdp->rxq->mem.type == MEM_TYPE_ZERO_COPY ||
+	    xdp->rxq->mem.type == MEM_TYPE_XSK_BUFF_POOL)
 		return xdp_convert_zc_to_xdp_frame(xdp);
 
 	/* Assure headroom is available for storing info */

include/net/xdp_sock.h

@@ -31,11 +31,13 @@ struct xdp_umem_fq_reuse {
 struct xdp_umem {
 	struct xsk_queue *fq;
 	struct xsk_queue *cq;
+	struct xsk_buff_pool *pool;
 	struct xdp_umem_page *pages;
 	u64 chunk_mask;
 	u64 size;
 	u32 headroom;
 	u32 chunk_size_nohr;
+	u32 chunk_size;
 	struct user_struct *user;
 	refcount_t users;
 	struct work_struct work;

include/net/xdp_sock_drv.h

@@ -7,6 +7,7 @@
 #define _LINUX_XDP_SOCK_DRV_H
 
 #include <net/xdp_sock.h>
+#include <net/xsk_buff_pool.h>
 
 #ifdef CONFIG_XDP_SOCKETS
 
@@ -101,6 +102,94 @@ static inline u32 xsk_umem_xdp_frame_sz(struct xdp_umem *umem)
 	return umem->chunk_size_nohr;
 }
 
+static inline u32 xsk_umem_get_headroom(struct xdp_umem *umem)
+{
+	return XDP_PACKET_HEADROOM + umem->headroom;
+}
+
+static inline u32 xsk_umem_get_chunk_size(struct xdp_umem *umem)
+{
+	return umem->chunk_size;
+}
+
+static inline u32 xsk_umem_get_rx_frame_size(struct xdp_umem *umem)
+{
+	return xsk_umem_get_chunk_size(umem) - xsk_umem_get_headroom(umem);
+}
+
+static inline void xsk_buff_set_rxq_info(struct xdp_umem *umem,
+					 struct xdp_rxq_info *rxq)
+{
+	xp_set_rxq_info(umem->pool, rxq);
+}
+
+static inline void xsk_buff_dma_unmap(struct xdp_umem *umem,
+				      unsigned long attrs)
+{
+	xp_dma_unmap(umem->pool, attrs);
+}
+
+static inline int xsk_buff_dma_map(struct xdp_umem *umem, struct device *dev,
+				   unsigned long attrs)
+{
+	return xp_dma_map(umem->pool, dev, attrs, umem->pgs, umem->npgs);
+}
+
+static inline dma_addr_t xsk_buff_xdp_get_dma(struct xdp_buff *xdp)
+{
+	struct xdp_buff_xsk *xskb = container_of(xdp, struct xdp_buff_xsk, xdp);
+
+	return xp_get_dma(xskb);
+}
+
+static inline dma_addr_t xsk_buff_xdp_get_frame_dma(struct xdp_buff *xdp)
+{
+	struct xdp_buff_xsk *xskb = container_of(xdp, struct xdp_buff_xsk, xdp);
+
+	return xp_get_frame_dma(xskb);
+}
+
+static inline struct xdp_buff *xsk_buff_alloc(struct xdp_umem *umem)
+{
+	return xp_alloc(umem->pool);
+}
+
+static inline bool xsk_buff_can_alloc(struct xdp_umem *umem, u32 count)
+{
+	return xp_can_alloc(umem->pool, count);
+}
+
+static inline void xsk_buff_free(struct xdp_buff *xdp)
+{
+	struct xdp_buff_xsk *xskb = container_of(xdp, struct xdp_buff_xsk, xdp);
+
+	xp_free(xskb);
+}
+
+static inline dma_addr_t xsk_buff_raw_get_dma(struct xdp_umem *umem, u64 addr)
+{
+	return xp_raw_get_dma(umem->pool, addr);
+}
+
+static inline void *xsk_buff_raw_get_data(struct xdp_umem *umem, u64 addr)
+{
+	return xp_raw_get_data(umem->pool, addr);
+}
+
+static inline void xsk_buff_dma_sync_for_cpu(struct xdp_buff *xdp)
+{
+	struct xdp_buff_xsk *xskb = container_of(xdp, struct xdp_buff_xsk, xdp);
+
+	xp_dma_sync_for_cpu(xskb);
+}
+
+static inline void xsk_buff_raw_dma_sync_for_device(struct xdp_umem *umem,
+						    dma_addr_t dma,
+						    size_t size)
+{
+	xp_dma_sync_for_device(umem->pool, dma, size);
+}
+
 #else
 
 static inline bool xsk_umem_has_addrs(struct xdp_umem *umem, u32 cnt)
@@ -212,6 +301,81 @@ static inline u32 xsk_umem_xdp_frame_sz(struct xdp_umem *umem)
 	return 0;
 }
 
+static inline u32 xsk_umem_get_headroom(struct xdp_umem *umem)
+{
+	return 0;
+}
+
+static inline u32 xsk_umem_get_chunk_size(struct xdp_umem *umem)
+{
+	return 0;
+}
+
+static inline u32 xsk_umem_get_rx_frame_size(struct xdp_umem *umem)
+{
+	return 0;
+}
+
+static inline void xsk_buff_set_rxq_info(struct xdp_umem *umem,
+					 struct xdp_rxq_info *rxq)
+{
+}
+
+static inline void xsk_buff_dma_unmap(struct xdp_umem *umem,
+				      unsigned long attrs)
+{
+}
+
+static inline int xsk_buff_dma_map(struct xdp_umem *umem, struct device *dev,
+				   unsigned long attrs)
+{
+	return 0;
+}
+
+static inline dma_addr_t xsk_buff_xdp_get_dma(struct xdp_buff *xdp)
+{
+	return 0;
+}
+
+static inline dma_addr_t xsk_buff_xdp_get_frame_dma(struct xdp_buff *xdp)
+{
+	return 0;
+}
+
+static inline struct xdp_buff *xsk_buff_alloc(struct xdp_umem *umem)
+{
+	return NULL;
+}
+
+static inline bool xsk_buff_can_alloc(struct xdp_umem *umem, u32 count)
+{
+	return false;
+}
+
+static inline void xsk_buff_free(struct xdp_buff *xdp)
+{
+}
+
+static inline dma_addr_t xsk_buff_raw_get_dma(struct xdp_umem *umem, u64 addr)
+{
+	return 0;
+}
+
+static inline void *xsk_buff_raw_get_data(struct xdp_umem *umem, u64 addr)
+{
+	return NULL;
+}
+
+static inline void xsk_buff_dma_sync_for_cpu(struct xdp_buff *xdp)
+{
+}
+
+static inline void xsk_buff_raw_dma_sync_for_device(struct xdp_umem *umem,
+						    dma_addr_t dma,
+						    size_t size)
+{
+}
+
 #endif /* CONFIG_XDP_SOCKETS */
 
 #endif /* _LINUX_XDP_SOCK_DRV_H */

include/net/xsk_buff_pool.h

@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright(c) 2020 Intel Corporation. */
+
+#ifndef XSK_BUFF_POOL_H_
+#define XSK_BUFF_POOL_H_
+
+#include <linux/types.h>
+#include <linux/dma-mapping.h>
+#include <net/xdp.h>
+
+struct xsk_buff_pool;
+struct xdp_rxq_info;
+struct xsk_queue;
+struct xdp_desc;
+struct device;
+struct page;
+
+struct xdp_buff_xsk {
+	struct xdp_buff xdp;
+	dma_addr_t dma;
+	dma_addr_t frame_dma;
+	struct xsk_buff_pool *pool;
+	bool unaligned;
+	u64 orig_addr;
+	struct list_head free_list_node;
+};
+
+/* AF_XDP core. */
+struct xsk_buff_pool *xp_create(struct page **pages, u32 nr_pages, u32 chunks,
+				u32 chunk_size, u32 headroom, u64 size,
+				bool unaligned);
+void xp_set_fq(struct xsk_buff_pool *pool, struct xsk_queue *fq);
+void xp_destroy(struct xsk_buff_pool *pool);
+void xp_release(struct xdp_buff_xsk *xskb);
+u64 xp_get_handle(struct xdp_buff_xsk *xskb);
+bool xp_validate_desc(struct xsk_buff_pool *pool, struct xdp_desc *desc);
+
+/* AF_XDP, and XDP core. */
+void xp_free(struct xdp_buff_xsk *xskb);
+
+/* AF_XDP ZC drivers, via xdp_sock_buff.h */
+void xp_set_rxq_info(struct xsk_buff_pool *pool, struct xdp_rxq_info *rxq);
+int xp_dma_map(struct xsk_buff_pool *pool, struct device *dev,
+	       unsigned long attrs, struct page **pages, u32 nr_pages);
+void xp_dma_unmap(struct xsk_buff_pool *pool, unsigned long attrs);
+struct xdp_buff *xp_alloc(struct xsk_buff_pool *pool);
+bool xp_can_alloc(struct xsk_buff_pool *pool, u32 count);
+void *xp_raw_get_data(struct xsk_buff_pool *pool, u64 addr);
+dma_addr_t xp_raw_get_dma(struct xsk_buff_pool *pool, u64 addr);
+dma_addr_t xp_get_dma(struct xdp_buff_xsk *xskb);
+dma_addr_t xp_get_frame_dma(struct xdp_buff_xsk *xskb);
+void xp_dma_sync_for_cpu(struct xdp_buff_xsk *xskb);
+void xp_dma_sync_for_device(struct xsk_buff_pool *pool, dma_addr_t dma,
+			    size_t size);
+
+#endif /* XSK_BUFF_POOL_H_ */