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Date: Fri, 8 Sep 2017 14:23:56 -0700 (PDT)
From: Stefano Stabellini <sstabellini@kernel.org>
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>
cc: Stefano Stabellini <sstabellini@kernel.org>, xen-devel@lists.xen.org,
        linux-kernel@vger.kernel.org, jgross@suse.com,
        Stefano Stabellini <stefano@aporeto.com>
Subject: Re: [PATCH v3 05/13] xen/pvcalls: implement connect command
In-Reply-To: <98a37ce0-468c-0938-a56d-31bbde177c91@oracle.com>
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On Sat, 12 Aug 2017, Boris Ostrovsky wrote:
> On 07/31/2017 06:57 PM, Stefano Stabellini wrote:
> > Send PVCALLS_CONNECT to the backend. Allocate a new ring and evtchn for
> > the active socket.
> > 
> > Introduce fields in struct sock_mapping to keep track of active sockets.
> > Introduce a waitqueue to allow the frontend to wait on data coming from
> > the backend on the active socket (recvmsg command).
> > 
> > Two mutexes (one of reads and one for writes) will be used to protect
> > the active socket in and out rings from concurrent accesses.
> > 
> > Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
> > CC: boris.ostrovsky@oracle.com
> > CC: jgross@suse.com
> > ---
> >   drivers/xen/pvcalls-front.c | 146
> > ++++++++++++++++++++++++++++++++++++++++++++
> >   drivers/xen/pvcalls-front.h |   2 +
> >   2 files changed, 148 insertions(+)
> > 
> > diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> > index 7c4a7cb..379b8fb 100644
> > --- a/drivers/xen/pvcalls-front.c
> > +++ b/drivers/xen/pvcalls-front.c
> > @@ -13,6 +13,10 @@
> >    */
> >     #include <linux/module.h>
> > +#include <linux/net.h>
> > +#include <linux/socket.h>
> > +
> > +#include <net/sock.h>
> >     #include <xen/events.h>
> >   #include <xen/grant_table.h>
> > @@ -44,6 +48,18 @@ struct sock_mapping {
> >   	bool active_socket;
> >   	struct list_head list;
> >   	struct socket *sock;
> > +	union {
> > +		struct {
> > +			int irq;
> > +			grant_ref_t ref;
> > +			struct pvcalls_data_intf *ring;
> > +			struct pvcalls_data data;
> > +			struct mutex in_mutex;
> > +			struct mutex out_mutex;
> > +
> > +			wait_queue_head_t inflight_conn_req;
> > +		} active;
> > +	};
> >   };
> >     static inline int get_request(struct pvcalls_bedata *bedata, int
> > *req_id)
> > @@ -97,6 +113,18 @@ static irqreturn_t pvcalls_front_event_handler(int irq,
> > void *dev_id)
> >   	return IRQ_HANDLED;
> >   }
> >   +static irqreturn_t pvcalls_front_conn_handler(int irq, void *sock_map)
> > +{
> > +	struct sock_mapping *map = sock_map;
> > +
> > +	if (map == NULL)
> > +		return IRQ_HANDLED;
> > +
> > +	wake_up_interruptible(&map->active.inflight_conn_req);
> > +
> > +	return IRQ_HANDLED;
> > +}
> > +
> >   int pvcalls_front_socket(struct socket *sock)
> >   {
> >   	struct pvcalls_bedata *bedata;
> > @@ -162,6 +190,124 @@ int pvcalls_front_socket(struct socket *sock)
> >   	return ret;
> >   }
> >   +static int create_active(struct sock_mapping *map, int *evtchn)
> > +{
> > +	void *bytes;
> > +	int ret = -ENOMEM, irq = -1, i;
> > +
> > +	init_waitqueue_head(&map->active.inflight_conn_req);
> > +
> > +	map->active.ring = (struct pvcalls_data_intf *)
> > +		__get_free_page(GFP_KERNEL | __GFP_ZERO);
> > +	if (map->active.ring == NULL)
> > +		goto out_error;
> > +	memset(map->active.ring, 0, XEN_PAGE_SIZE);
> 
> 
> Not needed (page allocated with __GFP_ZERO)

OK


> BTW, are you operating on XEN_PAGE_SIZE of PAGE_SIZE? Because if it's the
> former than __get_free_page() may be way more than what you need. (below too)

It is the former, but a 64K kernel is not able to allocate a 4K page, so
we'll have to accept the memory waste.

 
> > +	map->active.ring->ring_order = PVCALLS_RING_ORDER;
> > +	bytes = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
> > +					map->active.ring->ring_order);
> > +	if (bytes == NULL)
> > +		goto out_error;
> > +	for (i = 0; i < (1 << map->active.ring->ring_order); i++)
> 
> PVCALLS_RING_ORDER

OK

 
> > +		map->active.ring->ref[i] = gnttab_grant_foreign_access(
> > +			pvcalls_front_dev->otherend_id,
> > +			pfn_to_gfn(virt_to_pfn(bytes) + i), 0);
> > +
> > +	map->active.ref = gnttab_grant_foreign_access(
> > +		pvcalls_front_dev->otherend_id,
> > +		pfn_to_gfn(virt_to_pfn((void *)map->active.ring)), 0);
> > +
> > +	map->active.data.in = bytes;
> > +	map->active.data.out = bytes +
> > +		XEN_FLEX_RING_SIZE(map->active.ring->ring_order);
> > +
> > +	ret = xenbus_alloc_evtchn(pvcalls_front_dev, evtchn);
> > +	if (ret)
> > +		goto out_error;
> > +	irq = bind_evtchn_to_irqhandler(*evtchn, pvcalls_front_conn_handler,
> > +					0, "pvcalls-frontend", map);
> > +	if (irq < 0) {
> > +		ret = irq;
> > +		goto out_error;
> > +	}
> > +
> > +	map->active.irq = irq;
> > +	map->active_socket = true;
> > +	mutex_init(&map->active.in_mutex);
> > +	mutex_init(&map->active.out_mutex);
> > +
> > +	return 0;
> > +
> > +out_error:
> > +	if (irq >= 0)
> > +		unbind_from_irqhandler(irq, map);
> > +	else if (*evtchn >= 0)
> 
> *evtchn may have been passed in as >=0. You probably want to set to -1 or
> something in the beginning.

OK


> > +		xenbus_free_evtchn(pvcalls_front_dev, *evtchn);
> > +	kfree(map->active.data.in);
> > +	kfree(map->active.ring);
> > +	kfree(map);
> 
> Probably a matter of personal style but I think it's better to free map in the
> caller.
>
> Actually, should it be freed? The caller gets an error if get_request() or
> create_active() fail. In the first case map is not freed. Is the caller going
> to distinguish EAGAIN from any other error and know that map does not need to
> be allocated?

You are right, map shouldn't be freed, as "close" is still supposed to
be called afterwards, even if "connect" failed.


> (Also I think you need to unlink the map from socket_mapping list before
> freeing it).

As map shouldn't be freed, it should also not be removed by
socket_mapping.


> > +	return ret;
> > +}
> > +
> > +int pvcalls_front_connect(struct socket *sock, struct sockaddr *addr,
> > +				int addr_len, int flags)
> > +{
> > +	struct pvcalls_bedata *bedata;
> > +	struct sock_mapping *map = NULL;
> > +	struct xen_pvcalls_request *req;
> > +	int notify, req_id, ret, evtchn;
> > +
> > +	if (!pvcalls_front_dev)
> > +		return -ENETUNREACH;
> > +	if (addr->sa_family != AF_INET || sock->type != SOCK_STREAM)
> > +		return -ENOTSUPP;
> > +
> > +	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> > +
> > +	map = (struct sock_mapping *) READ_ONCE(sock->sk->sk_send_head);
> > +	if (!map)
> > +	    return -EINVAL;
> > +
> > +	spin_lock(&bedata->pvcallss_lock);
> > +	ret = get_request(bedata, &req_id);
> > +	if (ret < 0) {
> > +		spin_unlock(&bedata->pvcallss_lock);
> > +		return ret;
> > +	}
> > +	ret = create_active(map, &evtchn);
> > +	if (ret < 0) {
> > +		spin_unlock(&bedata->pvcallss_lock);
> > +		return ret;
> > +	}
> > +
> > +	req = RING_GET_REQUEST(&bedata->ring, req_id);
> > +	req->req_id = req_id;
> > +	req->cmd = PVCALLS_CONNECT;
> > +	req->u.connect.id = (uint64_t)map;
> > +	memcpy(req->u.connect.addr, addr, sizeof(*addr));
> > +	req->u.connect.len = addr_len;
> > +	req->u.connect.flags = flags;
> > +	req->u.connect.ref = map->active.ref;
> > +	req->u.connect.evtchn = evtchn;
> > +	
> > +	map->sock = sock;
> > +
> > +	bedata->ring.req_prod_pvt++;
> > +	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&bedata->ring, notify);
> > +	spin_unlock(&bedata->pvcallss_lock);
> > +
> > +	if (notify)
> > +		notify_remote_via_irq(bedata->irq);
> > +
> > +	wait_event(bedata->inflight_req,
> > +		   READ_ONCE(bedata->rsp[req_id].req_id) == req_id);
> > +
> > +	ret = bedata->rsp[req_id].ret;
> > +	/* read ret, then set this rsp slot to be reused */
> > +	smp_mb();
> > +	WRITE_ONCE(bedata->rsp[req_id].req_id, PVCALLS_INVALID_ID);
> > +	return ret;
> > +}
> > +
> >   static const struct xenbus_device_id pvcalls_front_ids[] = {
> >   	{ "pvcalls" },
> >   	{ "" }
> > diff --git a/drivers/xen/pvcalls-front.h b/drivers/xen/pvcalls-front.h
> > index b7dabed..63b0417 100644
> > --- a/drivers/xen/pvcalls-front.h
> > +++ b/drivers/xen/pvcalls-front.h
> > @@ -4,5 +4,7 @@
> >   #include <linux/net.h>
> >     int pvcalls_front_socket(struct socket *sock);
> > +int pvcalls_front_connect(struct socket *sock, struct sockaddr *addr,
> > +			  int addr_len, int flags);
> >     #endif
> > 
>