Subject: Re: [RFC PATCH v9 12/16] Add mp(mediate passthru) device.

From: "Michael S. Tsirkin" <[email-masked]>
Date: Mon, 20 Sep 2010 13:36:43 +0200

On Mon, Sep 20, 2010 at 04:08:48PM +0800, [email-masked] wrote:
> From: Xin Xiaohui <[email-masked]>
> 
> ---
> Michael,
> I have move the ioctl to configure the locked memory to vhost

It's ok to move this to vhost but vhost does not
know how much memory is needed by the backend.
So I think we'll need another ioctl in the backend
to tell userspace how much memory is needed?

It seems a bit cleaner as a backend ioctl as vhost
does not lock memory itself, but I am not
principally opposed.

> and 
> check the limit with mm->locked_vm. please have a look.
> 
> Thanks
> Xiaohui
> 
>  drivers/vhost/mpassthru.c |   74 +++++++++----------------------------------
>  drivers/vhost/net.c       |   78 ++++++++++++++++++++++++++++++++++++++------
>  include/linux/vhost.h     |    3 ++
>  3 files changed, 85 insertions(+), 70 deletions(-)
> 
> diff --git a/drivers/vhost/mpassthru.c b/drivers/vhost/mpassthru.c
> index d86d94c..fd3827b 100644
> --- a/drivers/vhost/mpassthru.c
> +++ b/drivers/vhost/mpassthru.c
> @@ -109,9 +109,6 @@ struct page_ctor {
>  	int			wq_len;
>  	int			rq_len;
>  	spinlock_t		read_lock;
> -	/* record the locked pages */
> -	int			lock_pages;
> -	struct rlimit		o_rlim;
>  	struct net_device	*dev;
>  	struct mpassthru_port	port;
>  	struct page_info	**hash_table;
> @@ -231,7 +228,6 @@ static int page_ctor_attach(struct mp_struct *mp)
>  	ctor->port.ctor = page_ctor;
>  	ctor->port.sock = &mp->socket;
>  	ctor->port.hash = mp_lookup;
> -	ctor->lock_pages = 0;
>  
>  	/* locked by mp_mutex */
>  	dev->mp_port = &ctor->port;
> @@ -264,37 +260,6 @@ struct page_info *info_dequeue(struct page_ctor *ctor)
>  	return info;
>  }
>  
> -static int set_memlock_rlimit(struct page_ctor *ctor, int resource,
> -			      unsigned long cur, unsigned long max)
> -{
> -	struct rlimit new_rlim, *old_rlim;
> -	int retval;
> -
> -	if (resource != RLIMIT_MEMLOCK)
> -		return -EINVAL;
> -	new_rlim.rlim_cur = cur;
> -	new_rlim.rlim_max = max;
> -
> -	old_rlim = current->signal->rlim + resource;
> -
> -	/* remember the old rlimit value when backend enabled */
> -	ctor->o_rlim.rlim_cur = old_rlim->rlim_cur;
> -	ctor->o_rlim.rlim_max = old_rlim->rlim_max;
> -
> -	if ((new_rlim.rlim_max > old_rlim->rlim_max) &&
> -			!capable(CAP_SYS_RESOURCE))
> -		return -EPERM;
> -
> -	retval = security_task_setrlimit(resource, &new_rlim);
> -	if (retval)
> -		return retval;
> -
> -	task_lock(current->group_leader);
> -	*old_rlim = new_rlim;
> -	task_unlock(current->group_leader);
> -	return 0;
> -}
> -
>  static void relinquish_resource(struct page_ctor *ctor)
>  {
>  	if (!(ctor->dev->flags & IFF_UP) &&
> @@ -322,8 +287,6 @@ static void mp_ki_dtor(struct kiocb *iocb)
>  		info->ctor->rq_len--;
>  	} else
>  		info->ctor->wq_len--;
> -	/* Decrement the number of locked pages */
> -	info->ctor->lock_pages -= info->pnum;
>  	kmem_cache_free(ext_page_info_cache, info);
>  	relinquish_resource(info->ctor);
>  
> @@ -349,7 +312,7 @@ static struct kiocb *create_iocb(struct page_info *info, int size)
>  	iocb->ki_dtor(iocb);
>  	iocb->private = (void *)info;
>  	iocb->ki_dtor = mp_ki_dtor;
> -
> +	iocb->ki_user_data = info->pnum;
>  	return iocb;
>  }
>  
> @@ -375,10 +338,6 @@ static int page_ctor_detach(struct mp_struct *mp)
>  
>  	relinquish_resource(ctor);
>  
> -	set_memlock_rlimit(ctor, RLIMIT_MEMLOCK,
> -			   ctor->o_rlim.rlim_cur,
> -			   ctor->o_rlim.rlim_max);
> -
>  	/* locked by mp_mutex */
>  	ctor->dev->mp_port = NULL;
>  	dev_put(ctor->dev);
> @@ -565,21 +524,23 @@ static struct page_info *alloc_page_info(struct page_ctor *ctor,
>  	int rc;
>  	int i, j, n = 0;
>  	int len;
> -	unsigned long base, lock_limit;
> +	unsigned long base, lock_limit, locked;
>  	struct page_info *info = NULL;
>  
> -	lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
> -	lock_limit >>= PAGE_SHIFT;
> +	down_write(&current->mm->mmap_sem);
> +	locked     = count + current->mm->locked_vm;
> +	lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
>  
> -	if (ctor->lock_pages + count > lock_limit && npages) {
> -		printk(KERN_INFO "exceed the locked memory rlimit.");
> -		return NULL;
> -	}
> +	if ((locked > lock_limit) && !capable(CAP_IPC_LOCK))
> +		goto out;
>  
>  	info = kmem_cache_alloc(ext_page_info_cache, GFP_KERNEL);
>  	
>  	if (!info)
> -		return NULL;
> +		goto out;
> +
> +	up_write(&current->mm->mmap_sem);
> +
>  	info->skb = NULL;
>  	info->next = info->prev = NULL;
>  

Sorry I wasnt clear, I didn't really mean we copy everything
from infiniband, just the capability checks and locked_mm use.
These guys don't do registration on data path so
they can play games with locked_mm etc on registration.
But lock on data path, taking mmap sem and doing security checks
on data path would be bad for performance.
I would expect this to cause contention especially
as we'll go for multiqueue.

Here's what I really meant:
	SET_MEM_LOCKED gets a 32 bit integer (or a 64 bit
	if you like - just not long).
	the meaning of which is "this is how much
	memory device can lock".
	This ioctl does rlim_cur and capability checks,
	if passed immediately increments locked_vm counter
	by the *maximum amount specified*.
	Device must store the value by which we incremented
	locked_vm and the mm pointer (if this is vhost ioctl
	it has the owner already). Let's call this
	field lock_limit.

	Lock limit can also take into account
	e.g. device tx queue depth and our queue size.
	Either we give another ioctl that tells userspace
	about these and let it make the decision,
	or simply cap lock_limit ourselves
	depending on these parameters.

	If another SET_MEM_LOCKED ioctl is made,
	decrement lcoked_vm in the stored mm,
	and redo the operation on current->mm
	(note: might be different!).

	This ioctl should probably fail if backend is active
	(already has locked some pages), such an
	approach makes it easy as we do not need to
	find and unlock pages.

	Each time you want to lock some memory you check that
	1. current->mm matches the stored mm.
	2. (number of pages locked + amount we want to lock) * PAGE_SIZE <= lock_limit.

	close and RESET_OWNER decrement and drop mm reference
	(note: on close
	we decrement owner's locked_vm, not current->mm
	which might be different).

> @@ -633,8 +594,7 @@ static struct page_info *alloc_page_info(struct page_ctor *ctor,
>  		for (i = 0; i < j; i++)
>  			mp_hash_insert(ctor, info->pages[i], info);
>  	}
> -	/* increment the number of locked pages */
> -	ctor->lock_pages += j;
> +
>  	return info;
>  
>  failed:
> @@ -642,7 +602,9 @@ failed:
>  		put_page(info->pages[i]);
>  
>  	kmem_cache_free(ext_page_info_cache, info);
> -
> +	return NULL;
> +out:
> +	up(&current->mm->mmap_sem);
>  	return NULL;
>  }
>  
> @@ -1006,12 +968,6 @@ proceed:
>  		count--;
>  	}
>  
> -	if (!ctor->lock_pages || !ctor->rq_len) {
> -		set_memlock_rlimit(ctor, RLIMIT_MEMLOCK,
> -				iocb->ki_user_data * 4096 * 2,
> -				iocb->ki_user_data * 4096 * 2);
> -	}
> -
>  	/* Translate address to kernel */
>  	info = alloc_page_info(ctor, iocb, iov, count, frags, npages, 0);
>  	if (!info)
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index c4bc815..da78837 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -42,6 +42,7 @@ enum {
>  };
>  
>  static struct kmem_cache *notify_cache;
> +static struct rlimit orig_rlim;
>  
>  enum vhost_net_poll_state {
>  	VHOST_NET_POLL_DISABLED = 0,
> @@ -136,13 +137,7 @@ static void handle_async_rx_events_notify(struct vhost_net *net,
>  	struct vhost_log *vq_log = NULL;
>  	int rx_total_len = 0;
>  	unsigned int head, log, in, out;
> -	int size;
> -	int count;
> -
> -	struct virtio_net_hdr_mrg_rxbuf hdr = {
> -		.hdr.flags = 0,
> -		.hdr.gso_type = VIRTIO_NET_HDR_GSO_NONE
> -	};
> +	int size, free = 0;
>  
>  	if (!is_async_vq(vq))
>  		return;
> @@ -160,7 +155,7 @@ static void handle_async_rx_events_notify(struct vhost_net *net,
>  			size = iocb->ki_nbytes;
>  			head = iocb->ki_pos;
>  			rx_total_len += iocb->ki_nbytes;
> -
> +			free += iocb->ki_user_data;
>  			if (iocb->ki_dtor)
>  				iocb->ki_dtor(iocb);
>  			kmem_cache_free(net->cache, iocb);
> @@ -192,6 +187,7 @@ static void handle_async_rx_events_notify(struct vhost_net *net,
>  					size = iocb->ki_nbytes;
>  					head = iocb->ki_pos;
>  					rx_total_len += iocb->ki_nbytes;
> +					free += iocb->ki_user_data;
>  
>  					if (iocb->ki_dtor)
>  						iocb->ki_dtor(iocb);
> @@ -211,7 +207,6 @@ static void handle_async_rx_events_notify(struct vhost_net *net,
>  					break;
>  
>  				i++;
> -				iocb == NULL;
>  				if (count)
>  					iocb = notify_dequeue(vq);
>  			}
> @@ -219,6 +214,10 @@ static void handle_async_rx_events_notify(struct vhost_net *net,
>  					&net->dev, vq, vq->heads, hc);
>  		}
>  	}
> +	/* record locked memroy */
> +	down_write(&current->mm->mmap_sem);
> +	current->mm->locked_vm -= free;
> +	up_write(&current->mm->mmap_sem);
>  }
>  
>  static void handle_async_tx_events_notify(struct vhost_net *net,
> @@ -227,7 +226,7 @@ static void handle_async_tx_events_notify(struct vhost_net *net,
>  	struct kiocb *iocb = NULL;
>  	struct list_head *entry, *tmp;
>  	unsigned long flags;
> -	int tx_total_len = 0;
> +	int tx_total_len = 0, free = 0;
>  
>  	if (!is_async_vq(vq))
>  		return;
> @@ -242,7 +241,7 @@ static void handle_async_tx_events_notify(struct vhost_net *net,
>  		vhost_add_used_and_signal(&net->dev, vq,
>  				iocb->ki_pos, 0);
>  		tx_total_len += iocb->ki_nbytes;
> -
> +		free += iocb->ki_user_data;
>  		if (iocb->ki_dtor)
>  			iocb->ki_dtor(iocb);
>  
> @@ -253,6 +252,10 @@ static void handle_async_tx_events_notify(struct vhost_net *net,
>  		}
>  	}
>  	spin_unlock_irqrestore(&vq->notify_lock, flags);
> +	/* record locked memroy */
> +	down_write(&current->mm->mmap_sem);
> +	current->mm->locked_vm -= free;
> +	up_write(&current->mm->mmap_sem);
>  }
>  
>  static struct kiocb *create_iocb(struct vhost_net *net,
> @@ -581,6 +584,7 @@ static void handle_rx_net(struct work_struct *work)
>  static int vhost_net_open(struct inode *inode, struct file *f)
>  {
>  	struct vhost_net *n = kmalloc(sizeof *n, GFP_KERNEL);
> +	struct rlimit *old_rlim;
>  	int r;
>  	if (!n)
>  		return -ENOMEM;
> @@ -597,6 +601,12 @@ static int vhost_net_open(struct inode *inode, struct file *f)
>  	n->tx_poll_state = VHOST_NET_POLL_DISABLED;
>  	n->cache = NULL;
>  
> +	old_rlim = current->signal->rlim + RLIMIT_MEMLOCK;
> +
> +	/* remember the old rlimit value when backend enabled */
> +	orig_rlim.rlim_cur = old_rlim->rlim_cur;
> +	orig_rlim.rlim_max = old_rlim->rlim_max;
> +
>  	f->private_data = n;
>  
>  	return 0;
> @@ -659,6 +669,39 @@ static void vhost_net_flush(struct vhost_net *n)
>  	vhost_net_flush_vq(n, VHOST_NET_VQ_RX);
>  }
>  
> +static long vhost_net_set_mem_locked(struct vhost_net *n,
> +				     unsigned long cur,
> +				     unsigned long max)
> +{

So one issue here is that when this is called on close,
current might be different from owner, with bad results.

I really think avoiding modifying rlimit is
the simplest way to go for now.

> +	struct rlimit new_rlim, *old_rlim;
> +	int retval = 0;
> +
> +	mutex_lock(&n->dev.mutex);
> +	new_rlim.rlim_cur = cur;
> +	new_rlim.rlim_max = max;
> +
> +	old_rlim = current->signal->rlim + RLIMIT_MEMLOCK;
> +
> +	if ((new_rlim.rlim_max > old_rlim->rlim_max) &&
> +			!capable(CAP_SYS_RESOURCE)) {
> +		retval = -EPERM;
> +		goto err;
> +	}
> +
> +	retval = security_task_setrlimit(RLIMIT_MEMLOCK, &new_rlim);
> +	if (retval) {
> +		retval = retval;
> +		goto err;
> +	}
> +
> +	task_lock(current->group_leader);
> +	*old_rlim = new_rlim;
> +	task_unlock(current->group_leader);
> +err:
> +	mutex_unlock(&n->dev.mutex);
> +	return retval;
> +}
> +
>  static void vhost_async_cleanup(struct vhost_net *n)
>  {
>  	/* clean the notifier */
> @@ -691,6 +734,10 @@ static int vhost_net_release(struct inode *inode, struct file *f)
>  	 * since jobs can re-queue themselves. */
>  	vhost_net_flush(n);
>  	vhost_async_cleanup(n);
> +	/* return back the rlimit */
> +	vhost_net_set_mem_locked(n,
> +				 orig_rlim.rlim_cur,
> +				 orig_rlim.rlim_max);
>  	kfree(n);
>  	return 0;
>  }
> @@ -846,6 +893,7 @@ err:
>  	return r;
>  }
>  
> +
>  static long vhost_net_reset_owner(struct vhost_net *n)
>  {
>  	struct socket *tx_sock = NULL;
> @@ -913,6 +961,7 @@ static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
>  	void __user *argp = (void __user *)arg;
>  	u64 __user *featurep = argp;
>  	struct vhost_vring_file backend;
> +	struct rlimit rlim;
>  	u64 features;
>  	int r;
>  	switch (ioctl) {
> @@ -933,6 +982,13 @@ static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
>  		return vhost_net_set_features(n, features);
>  	case VHOST_RESET_OWNER:
>  		return vhost_net_reset_owner(n);
> +	case VHOST_SET_MEM_LOCKED:
> +		r = copy_from_user(&rlim, argp, sizeof rlim);
> +		if (r < 0)
> +			return r;
> +		return vhost_net_set_mem_locked(n,
> +						rlim.rlim_cur,
> +						rlim.rlim_max);
>  	default:
>  		mutex_lock(&n->dev.mutex);
>  		r = vhost_dev_ioctl(&n->dev, ioctl, arg);
> diff --git a/include/linux/vhost.h b/include/linux/vhost.h
> index e847f1e..df93f5a 100644
> --- a/include/linux/vhost.h
> +++ b/include/linux/vhost.h
> @@ -92,6 +92,9 @@ struct vhost_memory {
>  /* Specify an eventfd file descriptor to signal on log write. */
>  #define VHOST_SET_LOG_FD _IOW(VHOST_VIRTIO, 0x07, int)
>  
> +/* Specify how much locked memory can be used */
> +#define VHOST_SET_MEM_LOCKED	_IOW(VHOST_VIRTIO, 0x08, struct rlimit)
> +

This is not a good structure to use: its size varies between
64 and 32 bit. rlimit64 would be better.
Also, you will have to include resource.h from here.

>  /* Ring setup. */
>  /* Set number of descriptors in ring. This parameter can not
>   * be modified while ring is running (bound to a device). */
> -- 
> 1.5.4.4