From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757311AbdIHXUb (ORCPT ); Fri, 8 Sep 2017 19:20:31 -0400 Received: from mail.kernel.org ([198.145.29.99]:42244 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757178AbdIHXUa (ORCPT ); Fri, 8 Sep 2017 19:20:30 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 80F0321977 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=sstabellini@kernel.org Date: Fri, 8 Sep 2017 16:20:28 -0700 (PDT) From: Stefano Stabellini X-X-Sender: sstabellini@sstabellini-ThinkPad-X260 To: Boris Ostrovsky cc: Stefano Stabellini , xen-devel@lists.xen.org, linux-kernel@vger.kernel.org, jgross@suse.com, Stefano Stabellini Subject: Re: [PATCH v3 04/13] xen/pvcalls: implement socket command and handle events In-Reply-To: Message-ID: References: <1501541855-7354-1-git-send-email-sstabellini@kernel.org> <1501541855-7354-4-git-send-email-sstabellini@kernel.org> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 12 Aug 2017, Boris Ostrovsky wrote: > On 07/31/2017 06:57 PM, Stefano Stabellini wrote: > > Send a PVCALLS_SOCKET command to the backend, use the masked > > req_prod_pvt as req_id. This way, req_id is guaranteed to be between 0 > > and PVCALLS_NR_REQ_PER_RING. We already have a slot in the rsp array > > ready for the response, and there cannot be two outstanding responses > > with the same req_id. > > > > Wait for the response by waiting on the inflight_req waitqueue and > > check for the req_id field in rsp[req_id]. Use atomic accesses and > > barriers to read the field. Note that the barriers are simple smp > > barriers (as opposed to virt barriers) because they are for internal > > frontend synchronization, not frontend<->backend communication. > > > > Once a response is received, clear the corresponding rsp slot by setting > > req_id to PVCALLS_INVALID_ID. Note that PVCALLS_INVALID_ID is invalid > > only from the frontend point of view. It is not part of the PVCalls > > protocol. > > > > pvcalls_front_event_handler is in charge of copying responses from the > > ring to the appropriate rsp slot. It is done by copying the body of the > > response first, then by copying req_id atomically. After the copies, > > wake up anybody waiting on waitqueue. > > > > pvcallss_lock protects accesses to the ring. > > > > Create a new struct sock_mapping and convert the pointer into an > > uint64_t and use it as id for the new socket to pass to the backend. The > > struct will be fully initialized later on connect or bind. In this patch > > the struct sock_mapping is empty, the fields will be added by the next > > patch. > > > > sock->sk->sk_send_head is not used for ip sockets: reuse the field to > > store a pointer to the struct sock_mapping corresponding to the socket. > > This way, we can easily get the struct sock_mapping from the struct > > socket. > > > > Signed-off-by: Stefano Stabellini > > CC: boris.ostrovsky@oracle.com > > CC: jgross@suse.com > > --- > > drivers/xen/pvcalls-front.c | 119 > > ++++++++++++++++++++++++++++++++++++++++++++ > > drivers/xen/pvcalls-front.h | 8 +++ > > 2 files changed, 127 insertions(+) > > create mode 100644 drivers/xen/pvcalls-front.h > > > > diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c > > index 2afe36d..7c4a7cb 100644 > > --- a/drivers/xen/pvcalls-front.c > > +++ b/drivers/xen/pvcalls-front.c > > @@ -20,6 +20,8 @@ > > #include > > #include > > +#include "pvcalls-front.h" > > + > > #define PVCALLS_INVALID_ID UINT_MAX > > #define PVCALLS_RING_ORDER XENBUS_MAX_RING_GRANT_ORDER > > #define PVCALLS_NR_REQ_PER_RING __CONST_RING_SIZE(xen_pvcalls, > > XEN_PAGE_SIZE) > > @@ -38,11 +40,128 @@ struct pvcalls_bedata { > > }; > > static struct xenbus_device *pvcalls_front_dev; > > +struct sock_mapping { > > + bool active_socket; > > + struct list_head list; > > + struct socket *sock; > > +}; > > + > > +static inline int get_request(struct pvcalls_bedata *bedata, int *req_id) > > +{ > > + *req_id = bedata->ring.req_prod_pvt & (RING_SIZE(&bedata->ring) - 1); > > + if (RING_FULL(&bedata->ring) || > > + READ_ONCE(bedata->rsp[*req_id].req_id) != PVCALLS_INVALID_ID) > > + return -EAGAIN; > > + return 0; > > +} > > + > > static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id) > > { > > + struct xenbus_device *dev = dev_id; > > + struct pvcalls_bedata *bedata; > > + struct xen_pvcalls_response *rsp; > > + uint8_t *src, *dst; > > + int req_id = 0, more = 0, done = 0; > > + > > + if (dev == NULL) > > + return IRQ_HANDLED; > > + > > + bedata = dev_get_drvdata(&dev->dev); > > + if (bedata == NULL) > > + return IRQ_HANDLED; > > + > > +again: > > + while (RING_HAS_UNCONSUMED_RESPONSES(&bedata->ring)) { > > + rsp = RING_GET_RESPONSE(&bedata->ring, bedata->ring.rsp_cons); > > + > > + req_id = rsp->req_id; > > + dst = (uint8_t *)&bedata->rsp[req_id] + sizeof(rsp->req_id); > > + src = (uint8_t *)rsp + sizeof(rsp->req_id); > > + memcpy(dst, src, sizeof(*rsp) - sizeof(rsp->req_id)); > > + /* > > + * First copy the rest of the data, then req_id. It is > > + * paired with the barrier when accessing bedata->rsp. > > + */ > > + smp_wmb(); > > + WRITE_ONCE(bedata->rsp[req_id].req_id, rsp->req_id); > > + > > + done = 1; > > + bedata->ring.rsp_cons++; > > + } > > + > > + RING_FINAL_CHECK_FOR_RESPONSES(&bedata->ring, more); > > + if (more) > > + goto again; > > + if (done) > > + wake_up(&bedata->inflight_req); > > return IRQ_HANDLED; > > } > > +int pvcalls_front_socket(struct socket *sock) > > +{ > > + struct pvcalls_bedata *bedata; > > + struct sock_mapping *map = NULL; > > + struct xen_pvcalls_request *req; > > + int notify, req_id, ret; > > + > > + if (!pvcalls_front_dev) > > + return -EACCES; > > + /* > > + * PVCalls only supports domain AF_INET, > > + * type SOCK_STREAM and protocol 0 sockets for now. > > + * > > + * Check socket type here, AF_INET and protocol checks are done > > + * by the caller. > > + */ > > + if (sock->type != SOCK_STREAM) > > + return -ENOTSUPP; > > + > > + bedata = dev_get_drvdata(&pvcalls_front_dev->dev); > > + > > + map = kzalloc(sizeof(*map), GFP_KERNEL); > > + if (map == NULL) > > + return -ENOMEM; > > + /* > > + * sock->sk->sk_send_head is not used for ip sockets: reuse the > > + * field to store a pointer to the struct sock_mapping > > + * corresponding to the socket. This way, we can easily get the > > + * struct sock_mapping from the struct socket. > > > Is this a safe assumption? Is it conceivable that at some point in the future > sk_send_head might become used? I don't think there is any risk of sk_send_head being used anytime soon: among all the protocols supported under net/, sk_send_head is only used by dccp. > > + */ > > + WRITE_ONCE(sock->sk->sk_send_head, (void *)map); > > + > > + spin_lock(&bedata->pvcallss_lock); > > + list_add_tail(&map->list, &bedata->socket_mappings); > > + > > + ret = get_request(bedata, &req_id); > > + if (ret < 0) { > > + spin_unlock(&bedata->pvcallss_lock); > > + return ret; > What is happening to the mapping you've linked above? Should it be unlinked > and freed? (or defer its creation until we've got a request slot?) Yes, you are right. > > + } > > + req = RING_GET_REQUEST(&bedata->ring, req_id); > > + req->req_id = req_id; > > + req->cmd = PVCALLS_SOCKET; > > + req->u.socket.id = (uint64_t) map; > > + req->u.socket.domain = AF_INET; > > + req->u.socket.type = SOCK_STREAM; > > + req->u.socket.protocol = 0; > > IPPROTO_IP? Yes, thanks