Subject: Re: [PATCH bpf-next 02/15] xsk: add user memory registration support sockopt

From: "Michael S. Tsirkin" <[email-masked]>
Date: Mon, 23 Apr 2018 19:18:07 +0300

On Mon, Apr 23, 2018 at 03:56:06PM +0200, Björn Töpel wrote:
> From: Björn Töpel <[email-masked]>
> 
> In this commit the base structure of the AF_XDP address family is set
> up. Further, we introduce the abilty register a window of user memory
> to the kernel via the XDP_UMEM_REG setsockopt syscall. The memory
> window is viewed by an AF_XDP socket as a set of equally large
> frames. After a user memory registration all frames are "owned" by the
> user application, and not the kernel.
> 
> Co-authored-by: Magnus Karlsson <[email-masked]>
> Signed-off-by: Magnus Karlsson <[email-masked]>
> Signed-off-by: Björn Töpel <[email-masked]>
> ---
>  include/uapi/linux/if_xdp.h |  34 +++++++
>  net/Makefile                |   1 +
>  net/xdp/Makefile            |   2 +
>  net/xdp/xdp_umem.c          | 237 ++++++++++++++++++++++++++++++++++++++++++++
>  net/xdp/xdp_umem.h          |  42 ++++++++
>  net/xdp/xdp_umem_props.h    |  23 +++++
>  net/xdp/xsk.c               | 223 +++++++++++++++++++++++++++++++++++++++++
>  7 files changed, 562 insertions(+)
>  create mode 100644 include/uapi/linux/if_xdp.h
>  create mode 100644 net/xdp/Makefile
>  create mode 100644 net/xdp/xdp_umem.c
>  create mode 100644 net/xdp/xdp_umem.h
>  create mode 100644 net/xdp/xdp_umem_props.h
>  create mode 100644 net/xdp/xsk.c
> 
> diff --git a/include/uapi/linux/if_xdp.h b/include/uapi/linux/if_xdp.h
> new file mode 100644
> index 000000000000..41252135a0fe
> --- /dev/null
> +++ b/include/uapi/linux/if_xdp.h
> @@ -0,0 +1,34 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note
> + *
> + * if_xdp: XDP socket user-space interface
> + * 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.
> + *
> + * Author(s): Björn Töpel <[email-masked]>
> + *	      Magnus Karlsson <[email-masked]>
> + */
> +
> +#ifndef _LINUX_IF_XDP_H
> +#define _LINUX_IF_XDP_H
> +
> +#include <linux/types.h>
> +
> +/* XDP socket options */
> +#define XDP_UMEM_REG			3
> +
> +struct xdp_umem_reg {
> +	__u64 addr; /* Start of packet data area */
> +	__u64 len; /* Length of packet data area */
> +	__u32 frame_size; /* Frame size */
> +	__u32 frame_headroom; /* Frame head room */
> +};
> +
> +#endif /* _LINUX_IF_XDP_H */
> diff --git a/net/Makefile b/net/Makefile
> index a6147c61b174..77aaddedbd29 100644
> --- a/net/Makefile
> +++ b/net/Makefile
> @@ -85,3 +85,4 @@ obj-y				+= l3mdev/
>  endif
>  obj-$(CONFIG_QRTR)		+= qrtr/
>  obj-$(CONFIG_NET_NCSI)		+= ncsi/
> +obj-$(CONFIG_XDP_SOCKETS)	+= xdp/
> diff --git a/net/xdp/Makefile b/net/xdp/Makefile
> new file mode 100644
> index 000000000000..a5d736640a0f
> --- /dev/null
> +++ b/net/xdp/Makefile
> @@ -0,0 +1,2 @@
> +obj-$(CONFIG_XDP_SOCKETS) += xsk.o xdp_umem.o
> +
> diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
> new file mode 100644
> index 000000000000..bff058f5a769
> --- /dev/null
> +++ b/net/xdp/xdp_umem.c
> @@ -0,0 +1,237 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* XDP user-space packet buffer
> + * 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/init.h>
> +#include <linux/sched/mm.h>
> +#include <linux/sched/signal.h>
> +#include <linux/sched/task.h>
> +#include <linux/uaccess.h>
> +#include <linux/slab.h>
> +#include <linux/bpf.h>
> +#include <linux/mm.h>
> +
> +#include "xdp_umem.h"
> +
> +#define XDP_UMEM_MIN_FRAME_SIZE 2048
> +
> +int xdp_umem_create(struct xdp_umem **umem)
> +{
> +	*umem = kzalloc(sizeof(**umem), GFP_KERNEL);
> +
> +	if (!(*umem))
> +		return -ENOMEM;
> +
> +	return 0;
> +}
> +
> +static void xdp_umem_unpin_pages(struct xdp_umem *umem)
> +{
> +	unsigned int i;
> +
> +	if (umem->pgs) {
> +		for (i = 0; i < umem->npgs; i++)

Since you pin them with FOLL_WRITE, I assume these pages
are written to.
Don't you need set_page_dirty_lock here?

> +			put_page(umem->pgs[i]);
> +
> +		kfree(umem->pgs);
> +		umem->pgs = NULL;
> +	}
> +}
> +
> +static void xdp_umem_unaccount_pages(struct xdp_umem *umem)
> +{
> +	if (umem->user) {
> +		atomic_long_sub(umem->npgs, &umem->user->locked_vm);
> +		free_uid(umem->user);
> +	}
> +}
> +
> +static void xdp_umem_release(struct xdp_umem *umem)
> +{
> +	struct task_struct *task;
> +	struct mm_struct *mm;
> +	unsigned long diff;
> +
> +	if (umem->pgs) {
> +		xdp_umem_unpin_pages(umem);
> +
> +		task = get_pid_task(umem->pid, PIDTYPE_PID);
> +		put_pid(umem->pid);
> +		if (!task)
> +			goto out;
> +		mm = get_task_mm(task);
> +		put_task_struct(task);
> +		if (!mm)
> +			goto out;
> +
> +		diff = umem->size >> PAGE_SHIFT;
> +
> +		down_write(&mm->mmap_sem);
> +		mm->pinned_vm -= diff;
> +		up_write(&mm->mmap_sem);
> +		mmput(mm);
> +		umem->pgs = NULL;
> +	}
> +
> +	xdp_umem_unaccount_pages(umem);
> +out:
> +	kfree(umem);
> +}
> +
> +void xdp_put_umem(struct xdp_umem *umem)
> +{
> +	if (!umem)
> +		return;
> +
> +	if (atomic_dec_and_test(&umem->users))
> +		xdp_umem_release(umem);
> +}
> +
> +static int xdp_umem_pin_pages(struct xdp_umem *umem)
> +{
> +	unsigned int gup_flags = FOLL_WRITE;
> +	long npgs;
> +	int err;
> +
> +	umem->pgs = kcalloc(umem->npgs, sizeof(*umem->pgs), GFP_KERNEL);
> +	if (!umem->pgs)
> +		return -ENOMEM;
> +
> +	npgs = get_user_pages(umem->address, umem->npgs,
> +			      gup_flags, &umem->pgs[0], NULL);
> +	if (npgs != umem->npgs) {
> +		if (npgs >= 0) {
> +			umem->npgs = npgs;
> +			err = -ENOMEM;
> +			goto out_pin;
> +		}
> +		err = npgs;
> +		goto out_pgs;
> +	}
> +	return 0;
> +
> +out_pin:
> +	xdp_umem_unpin_pages(umem);
> +out_pgs:
> +	kfree(umem->pgs);
> +	umem->pgs = NULL;
> +	return err;
> +}
> +
> +static int xdp_umem_account_pages(struct xdp_umem *umem)
> +{
> +	unsigned long lock_limit, new_npgs, old_npgs;
> +
> +	if (capable(CAP_IPC_LOCK))
> +		return 0;
> +
> +	lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> +	umem->user = get_uid(current_user());
> +
> +	do {
> +		old_npgs = atomic_long_read(&umem->user->locked_vm);
> +		new_npgs = old_npgs + umem->npgs;
> +		if (new_npgs > lock_limit) {
> +			free_uid(umem->user);
> +			umem->user = NULL;
> +			return -ENOBUFS;
> +		}
> +	} while (atomic_long_cmpxchg(&umem->user->locked_vm, old_npgs,
> +				     new_npgs) != old_npgs);
> +	return 0;
> +}
> +
> +static int __xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
> +{
> +	u32 frame_size = mr->frame_size, frame_headroom = mr->frame_headroom;
> +	u64 addr = mr->addr, size = mr->len;
> +	unsigned int nframes;
> +	int size_chk, err;
> +
> +	if (frame_size < XDP_UMEM_MIN_FRAME_SIZE || frame_size > PAGE_SIZE) {
> +		/* Strictly speaking we could support this, if:
> +		 * - huge pages, or*

what does "or*" here mean?

> +		 * - using an IOMMU, or
> +		 * - making sure the memory area is consecutive
> +		 * but for now, we simply say "computer says no".
> +		 */
> +		return -EINVAL;
> +	}
> +
> +	if (!is_power_of_2(frame_size))
> +		return -EINVAL;
> +
> +	if (!PAGE_ALIGNED(addr)) {
> +		/* Memory area has to be page size aligned. For
> +		 * simplicity, this might change.
> +		 */
> +		return -EINVAL;
> +	}
> +
> +	if ((addr + size) < addr)
> +		return -EINVAL;
> +
> +	nframes = size / frame_size;
> +	if (nframes == 0 || nframes > UINT_MAX)
> +		return -EINVAL;
> +
> +	frame_headroom = ALIGN(frame_headroom, 64);
> +
> +	size_chk = frame_size - frame_headroom - XDP_PACKET_HEADROOM;
> +	if (size_chk < 0)
> +		return -EINVAL;
> +
> +	umem->pid = get_task_pid(current, PIDTYPE_PID);
> +	umem->size = (size_t)size;
> +	umem->address = (unsigned long)addr;
> +	umem->props.frame_size = frame_size;
> +	umem->props.nframes = nframes;
> +	umem->frame_headroom = frame_headroom;
> +	umem->npgs = size / PAGE_SIZE;
> +	umem->pgs = NULL;
> +	umem->user = NULL;
> +
> +	umem->frame_size_log2 = ilog2(frame_size);
> +	umem->nfpp_mask = (PAGE_SIZE / frame_size) - 1;
> +	umem->nfpplog2 = ilog2(PAGE_SIZE / frame_size);
> +	atomic_set(&umem->users, 1);
> +
> +	err = xdp_umem_account_pages(umem);
> +	if (err)
> +		goto out;
> +
> +	err = xdp_umem_pin_pages(umem);
> +	if (err)
> +		goto out;
> +	return 0;
> +
> +out:
> +	put_pid(umem->pid);
> +	return err;
> +}
> +
> +int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
> +{
> +	int err;
> +
> +	if (!umem)
> +		return -EINVAL;
> +
> +	down_write(&current->mm->mmap_sem);
> +
> +	err = __xdp_umem_reg(umem, mr);
> +
> +	up_write(&current->mm->mmap_sem);
> +	return err;
> +}
> +
> diff --git a/net/xdp/xdp_umem.h b/net/xdp/xdp_umem.h
> new file mode 100644
> index 000000000000..58714f4f7f25
> --- /dev/null
> +++ b/net/xdp/xdp_umem.h
> @@ -0,0 +1,42 @@
> +/* SPDX-License-Identifier: GPL-2.0
> + * XDP user-space packet buffer
> + * 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 XDP_UMEM_H_
> +#define XDP_UMEM_H_
> +
> +#include <linux/mm.h>
> +#include <linux/if_xdp.h>
> +
> +#include "xdp_umem_props.h"
> +
> +struct xdp_umem {
> +	struct page **pgs;
> +	struct xdp_umem_props props;
> +	u32 npgs;
> +	u32 frame_headroom;
> +	u32 nfpp_mask;
> +	u32 nfpplog2;
> +	u32 frame_size_log2;
> +	struct user_struct *user;
> +	struct pid *pid;
> +	unsigned long address;
> +	size_t size;
> +	atomic_t users;
> +};
> +
> +int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr);
> +void xdp_put_umem(struct xdp_umem *umem);
> +int xdp_umem_create(struct xdp_umem **umem);
> +
> +#endif /* XDP_UMEM_H_ */
> diff --git a/net/xdp/xdp_umem_props.h b/net/xdp/xdp_umem_props.h
> new file mode 100644
> index 000000000000..77fb5daf29f3
> --- /dev/null
> +++ b/net/xdp/xdp_umem_props.h
> @@ -0,0 +1,23 @@
> +/* SPDX-License-Identifier: GPL-2.0
> + * XDP user-space packet buffer
> + * 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 XDP_UMEM_PROPS_H_
> +#define XDP_UMEM_PROPS_H_
> +
> +struct xdp_umem_props {
> +	u32 frame_size;
> +	u32 nframes;
> +};
> +
> +#endif /* XDP_UMEM_PROPS_H_ */
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> new file mode 100644
> index 000000000000..19fc719cbe0d
> --- /dev/null
> +++ b/net/xdp/xsk.c
> @@ -0,0 +1,223 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* XDP sockets
> + *
> + * AF_XDP sockets allows a channel between XDP programs and userspace
> + * applications.
> + * 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.
> + *
> + * Author(s): Björn Töpel <[email-masked]>
> + *	      Magnus Karlsson <[email-masked]>
> + */
> +
> +#define pr_fmt(fmt) "AF_XDP: %s: " fmt, __func__
> +
> +#include <linux/if_xdp.h>
> +#include <linux/init.h>
> +#include <linux/sched/mm.h>
> +#include <linux/sched/signal.h>
> +#include <linux/sched/task.h>
> +#include <linux/socket.h>
> +#include <linux/file.h>
> +#include <linux/uaccess.h>
> +#include <linux/net.h>
> +#include <linux/netdevice.h>
> +#include <net/sock.h>
> +
> +#include "xdp_umem.h"
> +
> +struct xdp_sock {
> +	/* struct sock must be the first member of struct xdp_sock */
> +	struct sock sk;
> +	struct xdp_umem *umem;
> +	/* Protects multiple processes in the control path */
> +	struct mutex mutex;
> +};
> +
> +static struct xdp_sock *xdp_sk(struct sock *sk)
> +{
> +	return (struct xdp_sock *)sk;
> +}
> +
> +static int xsk_release(struct socket *sock)
> +{
> +	struct sock *sk = sock->sk;
> +	struct net *net;
> +
> +	if (!sk)
> +		return 0;
> +
> +	net = sock_net(sk);
> +
> +	local_bh_disable();
> +	sock_prot_inuse_add(net, sk->sk_prot, -1);
> +	local_bh_enable();
> +
> +	sock_orphan(sk);
> +	sock->sk = NULL;
> +
> +	sk_refcnt_debug_release(sk);
> +	sock_put(sk);
> +
> +	return 0;
> +}
> +
> +static int xsk_setsockopt(struct socket *sock, int level, int optname,
> +			  char __user *optval, unsigned int optlen)
> +{
> +	struct sock *sk = sock->sk;
> +	struct xdp_sock *xs = xdp_sk(sk);
> +	int err;
> +
> +	if (level != SOL_XDP)
> +		return -ENOPROTOOPT;
> +
> +	switch (optname) {
> +	case XDP_UMEM_REG:
> +	{
> +		struct xdp_umem_reg mr;
> +		struct xdp_umem *umem;
> +
> +		if (xs->umem)
> +			return -EBUSY;
> +
> +		if (copy_from_user(&mr, optval, sizeof(mr)))
> +			return -EFAULT;
> +
> +		mutex_lock(&xs->mutex);
> +		err = xdp_umem_create(&umem);
> +
> +		err = xdp_umem_reg(umem, &mr);
> +		if (err) {
> +			kfree(umem);
> +			mutex_unlock(&xs->mutex);
> +			return err;
> +		}
> +
> +		/* Make sure umem is ready before it can be seen by others */
> +		smp_wmb();
> +
> +		xs->umem = umem;
> +		mutex_unlock(&xs->mutex);
> +		return 0;
> +	}
> +	default:
> +		break;
> +	}
> +
> +	return -ENOPROTOOPT;
> +}
> +
> +static struct proto xsk_proto = {
> +	.name =		"XDP",
> +	.owner =	THIS_MODULE,
> +	.obj_size =	sizeof(struct xdp_sock),
> +};
> +
> +static const struct proto_ops xsk_proto_ops = {
> +	.family =	PF_XDP,
> +	.owner =	THIS_MODULE,
> +	.release =	xsk_release,
> +	.bind =		sock_no_bind,
> +	.connect =	sock_no_connect,
> +	.socketpair =	sock_no_socketpair,
> +	.accept =	sock_no_accept,
> +	.getname =	sock_no_getname,
> +	.poll =		sock_no_poll,
> +	.ioctl =	sock_no_ioctl,
> +	.listen =	sock_no_listen,
> +	.shutdown =	sock_no_shutdown,
> +	.setsockopt =	xsk_setsockopt,
> +	.getsockopt =	sock_no_getsockopt,
> +	.sendmsg =	sock_no_sendmsg,
> +	.recvmsg =	sock_no_recvmsg,
> +	.mmap =		sock_no_mmap,
> +	.sendpage =	sock_no_sendpage,
> +};
> +
> +static void xsk_destruct(struct sock *sk)
> +{
> +	struct xdp_sock *xs = xdp_sk(sk);
> +
> +	if (!sock_flag(sk, SOCK_DEAD))
> +		return;
> +
> +	xdp_put_umem(xs->umem);
> +
> +	sk_refcnt_debug_dec(sk);
> +}
> +
> +static int xsk_create(struct net *net, struct socket *sock, int protocol,
> +		      int kern)
> +{
> +	struct sock *sk;
> +	struct xdp_sock *xs;
> +
> +	if (!ns_capable(net->user_ns, CAP_NET_RAW))
> +		return -EPERM;
> +	if (sock->type != SOCK_RAW)
> +		return -ESOCKTNOSUPPORT;
> +
> +	if (protocol)
> +		return -EPROTONOSUPPORT;
> +
> +	sock->state = SS_UNCONNECTED;
> +
> +	sk = sk_alloc(net, PF_XDP, GFP_KERNEL, &xsk_proto, kern);
> +	if (!sk)
> +		return -ENOBUFS;
> +
> +	sock->ops = &xsk_proto_ops;
> +
> +	sock_init_data(sock, sk);
> +
> +	sk->sk_family = PF_XDP;
> +
> +	sk->sk_destruct = xsk_destruct;
> +	sk_refcnt_debug_inc(sk);
> +
> +	xs = xdp_sk(sk);
> +	mutex_init(&xs->mutex);
> +
> +	local_bh_disable();
> +	sock_prot_inuse_add(net, &xsk_proto, 1);
> +	local_bh_enable();
> +
> +	return 0;
> +}
> +
> +static const struct net_proto_family xsk_family_ops = {
> +	.family = PF_XDP,
> +	.create = xsk_create,
> +	.owner	= THIS_MODULE,
> +};
> +
> +static int __init xsk_init(void)
> +{
> +	int err;
> +
> +	err = proto_register(&xsk_proto, 0 /* no slab */);
> +	if (err)
> +		goto out;
> +
> +	err = sock_register(&xsk_family_ops);
> +	if (err)
> +		goto out_proto;
> +
> +	return 0;
> +
> +out_proto:
> +	proto_unregister(&xsk_proto);
> +out:
> +	return err;
> +}
> +
> +fs_initcall(xsk_init);
> -- 
> 2.14.1