xsk: add umem fill queue support and mmap

Here, we add another setsockopt for registered user memory (umem)
called XDP_UMEM_FILL_QUEUE. Using this socket option, the process can
ask the kernel to allocate a queue (ring buffer) and also mmap it
(XDP_UMEM_PGOFF_FILL_QUEUE) into the process.

The queue is used to explicitly pass ownership of umem frames from the
user process to the kernel. These frames will in a later patch be
filled in with Rx packet data by the kernel.

v2: Fixed potential crash in xsk_mmap.

Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/uapi/linux/if_xdp.h

@@ -23,6 +23,7 @@
 
 /* XDP socket options */
 #define XDP_UMEM_REG			3
+#define XDP_UMEM_FILL_RING		4
 
 struct xdp_umem_reg {
 	__u64 addr; /* Start of packet data area */
@@ -31,4 +32,18 @@ struct xdp_umem_reg {
 	__u32 frame_headroom; /* Frame head room */
 };
 
+/* Pgoff for mmaping the rings */
+#define XDP_UMEM_PGOFF_FILL_RING	0x100000000
+
+struct xdp_ring {
+	__u32 producer __attribute__((aligned(64)));
+	__u32 consumer __attribute__((aligned(64)));
+};
+
+/* Used for the fill and completion queues for buffers */
+struct xdp_umem_ring {
+	struct xdp_ring ptrs;
+	__u32 desc[0] __attribute__((aligned(64)));
+};
+
 #endif /* _LINUX_IF_XDP_H */

net/xdp/Makefile

@@ -1,2 +1,2 @@
-obj-$(CONFIG_XDP_SOCKETS) += xsk.o xdp_umem.o
+obj-$(CONFIG_XDP_SOCKETS) += xsk.o xdp_umem.o xsk_queue.o
 

net/xdp/xdp_umem.c

@@ -65,6 +65,11 @@ static void xdp_umem_release(struct xdp_umem *umem)
 	struct task_struct *task;
 	struct mm_struct *mm;
 
+	if (umem->fq) {
+		xskq_destroy(umem->fq);
+		umem->fq = NULL;
+	}
+
 	if (umem->pgs) {
 		xdp_umem_unpin_pages(umem);
 

net/xdp/xdp_umem.h

@@ -19,9 +19,11 @@
 #include <linux/if_xdp.h>
 #include <linux/workqueue.h>
 
+#include "xsk_queue.h"
 #include "xdp_umem_props.h"
 
 struct xdp_umem {
+	struct xsk_queue *fq;
 	struct page **pgs;
 	struct xdp_umem_props props;
 	u32 npgs;

net/xdp/xsk.c

@@ -32,6 +32,7 @@
 #include <linux/netdevice.h>
 #include <net/xdp_sock.h>
 
+#include "xsk_queue.h"
 #include "xdp_umem.h"
 
 static struct xdp_sock *xdp_sk(struct sock *sk)
@@ -39,6 +40,21 @@ static struct xdp_sock *xdp_sk(struct sock *sk)
 	return (struct xdp_sock *)sk;
 }
 
+static int xsk_init_queue(u32 entries, struct xsk_queue **queue)
+{
+	struct xsk_queue *q;
+
+	if (entries == 0 || *queue || !is_power_of_2(entries))
+		return -EINVAL;
+
+	q = xskq_create(entries);
+	if (!q)
+		return -ENOMEM;
+
+	*queue = q;
+	return 0;
+}
+
 static int xsk_release(struct socket *sock)
 {
 	struct sock *sk = sock->sk;
@@ -101,6 +117,23 @@ static int xsk_setsockopt(struct socket *sock, int level, int optname,
 		mutex_unlock(&xs->mutex);
 		return 0;
 	}
+	case XDP_UMEM_FILL_RING:
+	{
+		struct xsk_queue **q;
+		int entries;
+
+		if (!xs->umem)
+			return -EINVAL;
+
+		if (copy_from_user(&entries, optval, sizeof(entries)))
+			return -EFAULT;
+
+		mutex_lock(&xs->mutex);
+		q = &xs->umem->fq;
+		err = xsk_init_queue(entries, q);
+		mutex_unlock(&xs->mutex);
+		return err;
+	}
 	default:
 		break;
 	}
@@ -108,6 +141,36 @@ static int xsk_setsockopt(struct socket *sock, int level, int optname,
 	return -ENOPROTOOPT;
 }
 
+static int xsk_mmap(struct file *file, struct socket *sock,
+		    struct vm_area_struct *vma)
+{
+	unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
+	unsigned long size = vma->vm_end - vma->vm_start;
+	struct xdp_sock *xs = xdp_sk(sock->sk);
+	struct xsk_queue *q = NULL;
+	unsigned long pfn;
+	struct page *qpg;
+
+	if (!xs->umem)
+		return -EINVAL;
+
+	if (offset == XDP_UMEM_PGOFF_FILL_RING)
+		q = xs->umem->fq;
+	else
+		return -EINVAL;
+
+	if (!q)
+		return -EINVAL;
+
+	qpg = virt_to_head_page(q->ring);
+	if (size > (PAGE_SIZE << compound_order(qpg)))
+		return -EINVAL;
+
+	pfn = virt_to_phys(q->ring) >> PAGE_SHIFT;
+	return remap_pfn_range(vma, vma->vm_start, pfn,
+			       size, vma->vm_page_prot);
+}
+
 static struct proto xsk_proto = {
 	.name =		"XDP",
 	.owner =	THIS_MODULE,
@@ -131,7 +194,7 @@ static const struct proto_ops xsk_proto_ops = {
 	.getsockopt =	sock_no_getsockopt,
 	.sendmsg =	sock_no_sendmsg,
 	.recvmsg =	sock_no_recvmsg,
-	.mmap =		sock_no_mmap,
+	.mmap =		xsk_mmap,
 	.sendpage =	sock_no_sendpage,
 };
 

net/xdp/xsk_queue.c

@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+/* XDP user-space ring structure
+ * Copyright(c) 2018 Intel Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ */
+
+#include <linux/slab.h>
+
+#include "xsk_queue.h"
+
+static u32 xskq_umem_get_ring_size(struct xsk_queue *q)
+{
+	return sizeof(struct xdp_umem_ring) + q->nentries * sizeof(u32);
+}
+
+struct xsk_queue *xskq_create(u32 nentries)
+{
+	struct xsk_queue *q;
+	gfp_t gfp_flags;
+	size_t size;
+
+	q = kzalloc(sizeof(*q), GFP_KERNEL);
+	if (!q)
+		return NULL;
+
+	q->nentries = nentries;
+	q->ring_mask = nentries - 1;
+
+	gfp_flags = GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN |
+		    __GFP_COMP  | __GFP_NORETRY;
+	size = xskq_umem_get_ring_size(q);
+
+	q->ring = (struct xdp_ring *)__get_free_pages(gfp_flags,
+						      get_order(size));
+	if (!q->ring) {
+		kfree(q);
+		return NULL;
+	}
+
+	return q;
+}
+
+void xskq_destroy(struct xsk_queue *q)
+{
+	if (!q)
+		return;
+
+	page_frag_free(q->ring);
+	kfree(q);
+}

net/xdp/xsk_queue.h

@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0
+ * XDP user-space ring structure
+ * Copyright(c) 2018 Intel Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ */
+
+#ifndef _LINUX_XSK_QUEUE_H
+#define _LINUX_XSK_QUEUE_H
+
+#include <linux/types.h>
+#include <linux/if_xdp.h>
+
+#include "xdp_umem_props.h"
+
+struct xsk_queue {
+	struct xdp_umem_props umem_props;
+	u32 ring_mask;
+	u32 nentries;
+	u32 prod_head;
+	u32 prod_tail;
+	u32 cons_head;
+	u32 cons_tail;
+	struct xdp_ring *ring;
+	u64 invalid_descs;
+};
+
+struct xsk_queue *xskq_create(u32 nentries);
+void xskq_destroy(struct xsk_queue *q);
+
+#endif /* _LINUX_XSK_QUEUE_H */