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

1 files changed, 467 insertions, 0 deletions

diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
new file mode 100644
index 000000000000..e214a5795a62
--- /dev/null
+++ b/net/xdp/xsk_buff_pool.c
@@ -0,0 +1,467 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <net/xsk_buff_pool.h>
+#include <net/xdp_sock.h>
+#include <linux/dma-direct.h>
+#include <linux/dma-noncoherent.h>
+#include <linux/swiotlb.h>
+
+#include "xsk_queue.h"
+
+struct xsk_buff_pool {
+	struct xsk_queue *fq;
+	struct list_head free_list;
+	dma_addr_t *dma_pages;
+	struct xdp_buff_xsk *heads;
+	u64 chunk_mask;
+	u64 addrs_cnt;
+	u32 free_list_cnt;
+	u32 dma_pages_cnt;
+	u32 heads_cnt;
+	u32 free_heads_cnt;
+	u32 headroom;
+	u32 chunk_size;
+	u32 frame_len;
+	bool cheap_dma;
+	bool unaligned;
+	void *addrs;
+	struct device *dev;
+	struct xdp_buff_xsk *free_heads[];
+};
+
+static void xp_addr_unmap(struct xsk_buff_pool *pool)
+{
+	vunmap(pool->addrs);
+}
+
+static int xp_addr_map(struct xsk_buff_pool *pool,
+		       struct page **pages, u32 nr_pages)
+{
+	pool->addrs = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);
+	if (!pool->addrs)
+		return -ENOMEM;
+	return 0;
+}
+
+void xp_destroy(struct xsk_buff_pool *pool)
+{
+	if (!pool)
+		return;
+
+	xp_addr_unmap(pool);
+	kvfree(pool->heads);
+	kvfree(pool);
+}
+
+struct xsk_buff_pool *xp_create(struct page **pages, u32 nr_pages, u32 chunks,
+				u32 chunk_size, u32 headroom, u64 size,
+				bool unaligned)
+{
+	struct xsk_buff_pool *pool;
+	struct xdp_buff_xsk *xskb;
+	int err;
+	u32 i;
+
+	pool = kvzalloc(struct_size(pool, free_heads, chunks), GFP_KERNEL);
+	if (!pool)
+		goto out;
+
+	pool->heads = kvcalloc(chunks, sizeof(*pool->heads), GFP_KERNEL);
+	if (!pool->heads)
+		goto out;
+
+	pool->chunk_mask = ~((u64)chunk_size - 1);
+	pool->addrs_cnt = size;
+	pool->heads_cnt = chunks;
+	pool->free_heads_cnt = chunks;
+	pool->headroom = headroom;
+	pool->chunk_size = chunk_size;
+	pool->cheap_dma = true;
+	pool->unaligned = unaligned;
+	pool->frame_len = chunk_size - headroom - XDP_PACKET_HEADROOM;
+	INIT_LIST_HEAD(&pool->free_list);
+
+	for (i = 0; i < pool->free_heads_cnt; i++) {
+		xskb = &pool->heads[i];
+		xskb->pool = pool;
+		xskb->xdp.frame_sz = chunk_size - headroom;
+		pool->free_heads[i] = xskb;
+	}
+
+	err = xp_addr_map(pool, pages, nr_pages);
+	if (!err)
+		return pool;
+
+out:
+	xp_destroy(pool);
+	return NULL;
+}
+
+void xp_set_fq(struct xsk_buff_pool *pool, struct xsk_queue *fq)
+{
+	pool->fq = fq;
+}
+
+void xp_set_rxq_info(struct xsk_buff_pool *pool, struct xdp_rxq_info *rxq)
+{
+	u32 i;
+
+	for (i = 0; i < pool->heads_cnt; i++)
+		pool->heads[i].xdp.rxq = rxq;
+}
+EXPORT_SYMBOL(xp_set_rxq_info);
+
+void xp_dma_unmap(struct xsk_buff_pool *pool, unsigned long attrs)
+{
+	dma_addr_t *dma;
+	u32 i;
+
+	if (pool->dma_pages_cnt == 0)
+		return;
+
+	for (i = 0; i < pool->dma_pages_cnt; i++) {
+		dma = &pool->dma_pages[i];
+		if (*dma) {
+			dma_unmap_page_attrs(pool->dev, *dma, PAGE_SIZE,
+					     DMA_BIDIRECTIONAL, attrs);
+			*dma = 0;
+		}
+	}
+
+	kvfree(pool->dma_pages);
+	pool->dma_pages_cnt = 0;
+	pool->dev = NULL;
+}
+EXPORT_SYMBOL(xp_dma_unmap);
+
+static void xp_check_dma_contiguity(struct xsk_buff_pool *pool)
+{
+	u32 i;
+
+	for (i = 0; i < pool->dma_pages_cnt - 1; i++) {
+		if (pool->dma_pages[i] + PAGE_SIZE == pool->dma_pages[i + 1])
+			pool->dma_pages[i] |= XSK_NEXT_PG_CONTIG_MASK;
+		else
+			pool->dma_pages[i] &= ~XSK_NEXT_PG_CONTIG_MASK;
+	}
+}
+
+static bool __maybe_unused xp_check_swiotlb_dma(struct xsk_buff_pool *pool)
+{
+#if defined(CONFIG_SWIOTLB)
+	phys_addr_t paddr;
+	u32 i;
+
+	for (i = 0; i < pool->dma_pages_cnt; i++) {
+		paddr = dma_to_phys(pool->dev, pool->dma_pages[i]);
+		if (is_swiotlb_buffer(paddr))
+			return false;
+	}
+#endif
+	return true;
+}
+
+static bool xp_check_cheap_dma(struct xsk_buff_pool *pool)
+{
+#if defined(CONFIG_HAS_DMA)
+	const struct dma_map_ops *ops = get_dma_ops(pool->dev);
+
+	if (ops) {
+		return !ops->sync_single_for_cpu &&
+			!ops->sync_single_for_device;
+	}
+
+	if (!dma_is_direct(ops))
+		return false;
+
+	if (!xp_check_swiotlb_dma(pool))
+		return false;
+
+	if (!dev_is_dma_coherent(pool->dev)) {
+#if defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU) ||		\
+	defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL) ||	\
+	defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE)
+		return false;
+#endif
+	}
+#endif
+	return true;
+}
+
+int xp_dma_map(struct xsk_buff_pool *pool, struct device *dev,
+	       unsigned long attrs, struct page **pages, u32 nr_pages)
+{
+	dma_addr_t dma;
+	u32 i;
+
+	pool->dma_pages = kvcalloc(nr_pages, sizeof(*pool->dma_pages),
+				   GFP_KERNEL);
+	if (!pool->dma_pages)
+		return -ENOMEM;
+
+	pool->dev = dev;
+	pool->dma_pages_cnt = nr_pages;
+
+	for (i = 0; i < pool->dma_pages_cnt; i++) {
+		dma = dma_map_page_attrs(dev, pages[i], 0, PAGE_SIZE,
+					 DMA_BIDIRECTIONAL, attrs);
+		if (dma_mapping_error(dev, dma)) {
+			xp_dma_unmap(pool, attrs);
+			return -ENOMEM;
+		}
+		pool->dma_pages[i] = dma;
+	}
+
+	if (pool->unaligned)
+		xp_check_dma_contiguity(pool);
+
+	pool->dev = dev;
+	pool->cheap_dma = xp_check_cheap_dma(pool);
+	return 0;
+}
+EXPORT_SYMBOL(xp_dma_map);
+
+static bool xp_desc_crosses_non_contig_pg(struct xsk_buff_pool *pool,
+					  u64 addr, u32 len)
+{
+	bool cross_pg = (addr & (PAGE_SIZE - 1)) + len > PAGE_SIZE;
+
+	if (pool->dma_pages_cnt && cross_pg) {
+		return !(pool->dma_pages[addr >> PAGE_SHIFT] &
+			 XSK_NEXT_PG_CONTIG_MASK);
+	}
+	return false;
+}
+
+static bool xp_addr_crosses_non_contig_pg(struct xsk_buff_pool *pool,
+					  u64 addr)
+{
+	return xp_desc_crosses_non_contig_pg(pool, addr, pool->chunk_size);
+}
+
+void xp_release(struct xdp_buff_xsk *xskb)
+{
+	xskb->pool->free_heads[xskb->pool->free_heads_cnt++] = xskb;
+}
+
+static u64 xp_aligned_extract_addr(struct xsk_buff_pool *pool, u64 addr)
+{
+	return addr & pool->chunk_mask;
+}
+
+static u64 xp_unaligned_extract_addr(u64 addr)
+{
+	return addr & XSK_UNALIGNED_BUF_ADDR_MASK;
+}
+
+static u64 xp_unaligned_extract_offset(u64 addr)
+{
+	return addr >> XSK_UNALIGNED_BUF_OFFSET_SHIFT;
+}
+
+static u64 xp_unaligned_add_offset_to_addr(u64 addr)
+{
+	return xp_unaligned_extract_addr(addr) +
+		xp_unaligned_extract_offset(addr);
+}
+
+static bool xp_check_unaligned(struct xsk_buff_pool *pool, u64 *addr)
+{
+	*addr = xp_unaligned_extract_addr(*addr);
+	if (*addr >= pool->addrs_cnt ||
+	    *addr + pool->chunk_size > pool->addrs_cnt ||
+	    xp_addr_crosses_non_contig_pg(pool, *addr))
+		return false;
+	return true;
+}
+
+static bool xp_check_aligned(struct xsk_buff_pool *pool, u64 *addr)
+{
+	*addr = xp_aligned_extract_addr(pool, *addr);
+	return *addr < pool->addrs_cnt;
+}
+
+static struct xdp_buff_xsk *__xp_alloc(struct xsk_buff_pool *pool)
+{
+	struct xdp_buff_xsk *xskb;
+	u64 addr;
+	bool ok;
+
+	if (pool->free_heads_cnt == 0)
+		return NULL;
+
+	xskb = pool->free_heads[--pool->free_heads_cnt];
+
+	for (;;) {
+		if (!xskq_cons_peek_addr_unchecked(pool->fq, &addr)) {
+			xp_release(xskb);
+			return NULL;
+		}
+
+		ok = pool->unaligned ? xp_check_unaligned(pool, &addr) :
+		     xp_check_aligned(pool, &addr);
+		if (!ok) {
+			pool->fq->invalid_descs++;
+			xskq_cons_release(pool->fq);
+			continue;
+		}
+		break;
+	}
+	xskq_cons_release(pool->fq);
+
+	xskb->orig_addr = addr;
+	xskb->xdp.data_hard_start = pool->addrs + addr + pool->headroom;
+	if (pool->dma_pages_cnt) {
+		xskb->frame_dma = (pool->dma_pages[addr >> PAGE_SHIFT] &
+				   ~XSK_NEXT_PG_CONTIG_MASK) +
+				  (addr & ~PAGE_MASK);
+		xskb->dma = xskb->frame_dma + pool->headroom +
+			    XDP_PACKET_HEADROOM;
+	}
+	return xskb;
+}
+
+struct xdp_buff *xp_alloc(struct xsk_buff_pool *pool)
+{
+	struct xdp_buff_xsk *xskb;
+
+	if (!pool->free_list_cnt) {
+		xskb = __xp_alloc(pool);
+		if (!xskb)
+			return NULL;
+	} else {
+		pool->free_list_cnt--;
+		xskb = list_first_entry(&pool->free_list, struct xdp_buff_xsk,
+					free_list_node);
+		list_del(&xskb->free_list_node);
+	}
+
+	xskb->xdp.data = xskb->xdp.data_hard_start + XDP_PACKET_HEADROOM;
+	xskb->xdp.data_meta = xskb->xdp.data;
+
+	if (!pool->cheap_dma) {
+		dma_sync_single_range_for_device(pool->dev, xskb->dma, 0,
+						 pool->frame_len,
+						 DMA_BIDIRECTIONAL);
+	}
+	return &xskb->xdp;
+}
+EXPORT_SYMBOL(xp_alloc);
+
+bool xp_can_alloc(struct xsk_buff_pool *pool, u32 count)
+{
+	if (pool->free_list_cnt >= count)
+		return true;
+	return xskq_cons_has_entries(pool->fq, count - pool->free_list_cnt);
+}
+EXPORT_SYMBOL(xp_can_alloc);
+
+void xp_free(struct xdp_buff_xsk *xskb)
+{
+	xskb->pool->free_list_cnt++;
+	list_add(&xskb->free_list_node, &xskb->pool->free_list);
+}
+EXPORT_SYMBOL(xp_free);
+
+static bool xp_aligned_validate_desc(struct xsk_buff_pool *pool,
+				     struct xdp_desc *desc)
+{
+	u64 chunk, chunk_end;
+
+	chunk = xp_aligned_extract_addr(pool, desc->addr);
+	chunk_end = xp_aligned_extract_addr(pool, desc->addr + desc->len);
+	if (chunk != chunk_end)
+		return false;
+
+	if (chunk >= pool->addrs_cnt)
+		return false;
+
+	if (desc->options)
+		return false;
+	return true;
+}
+
+static bool xp_unaligned_validate_desc(struct xsk_buff_pool *pool,
+				       struct xdp_desc *desc)
+{
+	u64 addr, base_addr;
+
+	base_addr = xp_unaligned_extract_addr(desc->addr);
+	addr = xp_unaligned_add_offset_to_addr(desc->addr);
+
+	if (desc->len > pool->chunk_size)
+		return false;
+
+	if (base_addr >= pool->addrs_cnt || addr >= pool->addrs_cnt ||
+	    xp_desc_crosses_non_contig_pg(pool, addr, desc->len))
+		return false;
+
+	if (desc->options)
+		return false;
+	return true;
+}
+
+bool xp_validate_desc(struct xsk_buff_pool *pool, struct xdp_desc *desc)
+{
+	return pool->unaligned ? xp_unaligned_validate_desc(pool, desc) :
+		xp_aligned_validate_desc(pool, desc);
+}
+
+u64 xp_get_handle(struct xdp_buff_xsk *xskb)
+{
+	u64 offset = xskb->xdp.data - xskb->xdp.data_hard_start;
+
+	offset += xskb->pool->headroom;
+	if (!xskb->pool->unaligned)
+		return xskb->orig_addr + offset;
+	return xskb->orig_addr + (offset << XSK_UNALIGNED_BUF_OFFSET_SHIFT);
+}
+
+void *xp_raw_get_data(struct xsk_buff_pool *pool, u64 addr)
+{
+	addr = pool->unaligned ? xp_unaligned_add_offset_to_addr(addr) : addr;
+	return pool->addrs + addr;
+}
+EXPORT_SYMBOL(xp_raw_get_data);
+
+dma_addr_t xp_raw_get_dma(struct xsk_buff_pool *pool, u64 addr)
+{
+	addr = pool->unaligned ? xp_unaligned_add_offset_to_addr(addr) : addr;
+	return (pool->dma_pages[addr >> PAGE_SHIFT] &
+		~XSK_NEXT_PG_CONTIG_MASK) +
+		(addr & ~PAGE_MASK);
+}
+EXPORT_SYMBOL(xp_raw_get_dma);
+
+dma_addr_t xp_get_dma(struct xdp_buff_xsk *xskb)
+{
+	return xskb->dma;
+}
+EXPORT_SYMBOL(xp_get_dma);
+
+dma_addr_t xp_get_frame_dma(struct xdp_buff_xsk *xskb)
+{
+	return xskb->frame_dma;
+}
+EXPORT_SYMBOL(xp_get_frame_dma);
+
+void xp_dma_sync_for_cpu(struct xdp_buff_xsk *xskb)
+{
+	if (xskb->pool->cheap_dma)
+		return;
+
+	dma_sync_single_range_for_cpu(xskb->pool->dev, xskb->dma, 0,
+				      xskb->pool->frame_len, DMA_BIDIRECTIONAL);
+}
+EXPORT_SYMBOL(xp_dma_sync_for_cpu);
+
+void xp_dma_sync_for_device(struct xsk_buff_pool *pool, dma_addr_t dma,
+			    size_t size)
+{
+	if (pool->cheap_dma)
+		return;
+
+	dma_sync_single_range_for_device(pool->dev, dma, 0,
+					 size, DMA_BIDIRECTIONAL);
+}
+EXPORT_SYMBOL(xp_dma_sync_for_device);