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29fee6eed2
Commitfd8aa9095a
("xen: optimize xenbus driver for multiple concurrent xenstore accesses") optimized xenbus concurrent accesses but in doing so broke UABI of /dev/xen/xenbus. Through /dev/xen/xenbus applications are in charge of xenbus message exchange with the correct header and body. Now, after the mentioned commit the replies received by application will no longer have the header req_id echoed back as it was on request (see specification below for reference), because that particular field is being overwritten by kernel. struct xsd_sockmsg { uint32_t type; /* XS_??? */ uint32_t req_id;/* Request identifier, echoed in daemon's response. */ uint32_t tx_id; /* Transaction id (0 if not related to a transaction). */ uint32_t len; /* Length of data following this. */ /* Generally followed by nul-terminated string(s). */ }; Before there was only one request at a time so req_id could simply be forwarded back and forth. To allow simultaneous requests we need a different req_id for each message thus kernel keeps a monotonic increasing counter for this field and is written on every request irrespective of userspace value. Forwarding again the req_id on userspace requests is not a solution because we would open the possibility of userspace-generated req_id colliding with kernel ones. So this patch instead takes another route which is to artificially keep user req_id while keeping the xenbus logic as is. We do that by saving the original req_id before xs_send(), use the private kernel counter as req_id and then once reply comes and was validated, we restore back the original req_id. Cc: <stable@vger.kernel.org> # 4.11 Fixes:fd8aa9095a
("xen: optimize xenbus driver for multiple concurrent xenstore accesses") Reported-by: Bhavesh Davda <bhavesh.davda@oracle.com> Signed-off-by: Joao Martins <joao.m.martins@oracle.com> Reviewed-by: Juergen Gross <jgross@suse.com> Signed-off-by: Juergen Gross <jgross@suse.com>
489 lines
11 KiB
C
489 lines
11 KiB
C
/******************************************************************************
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* xenbus_comms.c
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*
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* Low level code to talks to Xen Store: ringbuffer and event channel.
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*
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* Copyright (C) 2005 Rusty Russell, IBM Corporation
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License version 2
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* as published by the Free Software Foundation; or, when distributed
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* separately from the Linux kernel or incorporated into other
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* software packages, subject to the following license:
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this source file (the "Software"), to deal in the Software without
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* restriction, including without limitation the rights to use, copy, modify,
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* merge, publish, distribute, sublicense, and/or sell copies of the Software,
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* and to permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
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* IN THE SOFTWARE.
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/wait.h>
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#include <linux/interrupt.h>
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#include <linux/kthread.h>
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#include <linux/sched.h>
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#include <linux/err.h>
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#include <xen/xenbus.h>
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#include <asm/xen/hypervisor.h>
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#include <xen/events.h>
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#include <xen/page.h>
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#include "xenbus.h"
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/* A list of replies. Currently only one will ever be outstanding. */
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LIST_HEAD(xs_reply_list);
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/* A list of write requests. */
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LIST_HEAD(xb_write_list);
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DECLARE_WAIT_QUEUE_HEAD(xb_waitq);
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DEFINE_MUTEX(xb_write_mutex);
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/* Protect xenbus reader thread against save/restore. */
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DEFINE_MUTEX(xs_response_mutex);
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static int xenbus_irq;
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static struct task_struct *xenbus_task;
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static DECLARE_WORK(probe_work, xenbus_probe);
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static irqreturn_t wake_waiting(int irq, void *unused)
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{
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if (unlikely(xenstored_ready == 0)) {
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xenstored_ready = 1;
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schedule_work(&probe_work);
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}
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wake_up(&xb_waitq);
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return IRQ_HANDLED;
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}
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static int check_indexes(XENSTORE_RING_IDX cons, XENSTORE_RING_IDX prod)
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{
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return ((prod - cons) <= XENSTORE_RING_SIZE);
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}
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static void *get_output_chunk(XENSTORE_RING_IDX cons,
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XENSTORE_RING_IDX prod,
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char *buf, uint32_t *len)
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{
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*len = XENSTORE_RING_SIZE - MASK_XENSTORE_IDX(prod);
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if ((XENSTORE_RING_SIZE - (prod - cons)) < *len)
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*len = XENSTORE_RING_SIZE - (prod - cons);
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return buf + MASK_XENSTORE_IDX(prod);
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}
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static const void *get_input_chunk(XENSTORE_RING_IDX cons,
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XENSTORE_RING_IDX prod,
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const char *buf, uint32_t *len)
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{
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*len = XENSTORE_RING_SIZE - MASK_XENSTORE_IDX(cons);
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if ((prod - cons) < *len)
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*len = prod - cons;
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return buf + MASK_XENSTORE_IDX(cons);
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}
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static int xb_data_to_write(void)
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{
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struct xenstore_domain_interface *intf = xen_store_interface;
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return (intf->req_prod - intf->req_cons) != XENSTORE_RING_SIZE &&
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!list_empty(&xb_write_list);
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}
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/**
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* xb_write - low level write
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* @data: buffer to send
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* @len: length of buffer
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*
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* Returns number of bytes written or -err.
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*/
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static int xb_write(const void *data, unsigned int len)
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{
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struct xenstore_domain_interface *intf = xen_store_interface;
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XENSTORE_RING_IDX cons, prod;
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unsigned int bytes = 0;
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while (len != 0) {
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void *dst;
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unsigned int avail;
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/* Read indexes, then verify. */
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cons = intf->req_cons;
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prod = intf->req_prod;
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if (!check_indexes(cons, prod)) {
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intf->req_cons = intf->req_prod = 0;
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return -EIO;
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}
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if (!xb_data_to_write())
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return bytes;
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/* Must write data /after/ reading the consumer index. */
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virt_mb();
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dst = get_output_chunk(cons, prod, intf->req, &avail);
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if (avail == 0)
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continue;
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if (avail > len)
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avail = len;
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memcpy(dst, data, avail);
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data += avail;
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len -= avail;
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bytes += avail;
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/* Other side must not see new producer until data is there. */
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virt_wmb();
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intf->req_prod += avail;
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/* Implies mb(): other side will see the updated producer. */
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if (prod <= intf->req_cons)
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notify_remote_via_evtchn(xen_store_evtchn);
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}
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return bytes;
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}
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static int xb_data_to_read(void)
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{
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struct xenstore_domain_interface *intf = xen_store_interface;
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return (intf->rsp_cons != intf->rsp_prod);
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}
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static int xb_read(void *data, unsigned int len)
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{
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struct xenstore_domain_interface *intf = xen_store_interface;
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XENSTORE_RING_IDX cons, prod;
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unsigned int bytes = 0;
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while (len != 0) {
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unsigned int avail;
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const char *src;
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/* Read indexes, then verify. */
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cons = intf->rsp_cons;
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prod = intf->rsp_prod;
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if (cons == prod)
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return bytes;
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if (!check_indexes(cons, prod)) {
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intf->rsp_cons = intf->rsp_prod = 0;
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return -EIO;
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}
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src = get_input_chunk(cons, prod, intf->rsp, &avail);
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if (avail == 0)
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continue;
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if (avail > len)
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avail = len;
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/* Must read data /after/ reading the producer index. */
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virt_rmb();
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memcpy(data, src, avail);
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data += avail;
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len -= avail;
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bytes += avail;
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/* Other side must not see free space until we've copied out */
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virt_mb();
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intf->rsp_cons += avail;
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/* Implies mb(): other side will see the updated consumer. */
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if (intf->rsp_prod - cons >= XENSTORE_RING_SIZE)
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notify_remote_via_evtchn(xen_store_evtchn);
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}
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return bytes;
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}
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static int process_msg(void)
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{
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static struct {
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struct xsd_sockmsg msg;
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char *body;
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union {
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void *alloc;
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struct xs_watch_event *watch;
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};
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bool in_msg;
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bool in_hdr;
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unsigned int read;
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} state;
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struct xb_req_data *req;
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int err;
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unsigned int len;
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if (!state.in_msg) {
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state.in_msg = true;
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state.in_hdr = true;
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state.read = 0;
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/*
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* We must disallow save/restore while reading a message.
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* A partial read across s/r leaves us out of sync with
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* xenstored.
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* xs_response_mutex is locked as long as we are processing one
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* message. state.in_msg will be true as long as we are holding
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* the lock here.
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*/
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mutex_lock(&xs_response_mutex);
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if (!xb_data_to_read()) {
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/* We raced with save/restore: pending data 'gone'. */
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mutex_unlock(&xs_response_mutex);
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state.in_msg = false;
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return 0;
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}
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}
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if (state.in_hdr) {
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if (state.read != sizeof(state.msg)) {
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err = xb_read((void *)&state.msg + state.read,
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sizeof(state.msg) - state.read);
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if (err < 0)
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goto out;
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state.read += err;
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if (state.read != sizeof(state.msg))
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return 0;
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if (state.msg.len > XENSTORE_PAYLOAD_MAX) {
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err = -EINVAL;
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goto out;
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}
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}
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len = state.msg.len + 1;
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if (state.msg.type == XS_WATCH_EVENT)
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len += sizeof(*state.watch);
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state.alloc = kmalloc(len, GFP_NOIO | __GFP_HIGH);
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if (!state.alloc)
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return -ENOMEM;
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if (state.msg.type == XS_WATCH_EVENT)
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state.body = state.watch->body;
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else
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state.body = state.alloc;
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state.in_hdr = false;
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state.read = 0;
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}
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err = xb_read(state.body + state.read, state.msg.len - state.read);
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if (err < 0)
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goto out;
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state.read += err;
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if (state.read != state.msg.len)
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return 0;
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state.body[state.msg.len] = '\0';
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if (state.msg.type == XS_WATCH_EVENT) {
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state.watch->len = state.msg.len;
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err = xs_watch_msg(state.watch);
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} else {
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err = -ENOENT;
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mutex_lock(&xb_write_mutex);
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list_for_each_entry(req, &xs_reply_list, list) {
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if (req->msg.req_id == state.msg.req_id) {
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list_del(&req->list);
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err = 0;
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break;
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}
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}
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mutex_unlock(&xb_write_mutex);
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if (err)
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goto out;
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if (req->state == xb_req_state_wait_reply) {
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req->msg.req_id = req->caller_req_id;
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req->msg.type = state.msg.type;
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req->msg.len = state.msg.len;
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req->body = state.body;
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req->state = xb_req_state_got_reply;
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req->cb(req);
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} else
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kfree(req);
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}
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mutex_unlock(&xs_response_mutex);
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state.in_msg = false;
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state.alloc = NULL;
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return err;
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out:
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mutex_unlock(&xs_response_mutex);
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state.in_msg = false;
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kfree(state.alloc);
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state.alloc = NULL;
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return err;
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}
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static int process_writes(void)
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{
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static struct {
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struct xb_req_data *req;
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int idx;
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unsigned int written;
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} state;
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void *base;
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unsigned int len;
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int err = 0;
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if (!xb_data_to_write())
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return 0;
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mutex_lock(&xb_write_mutex);
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if (!state.req) {
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state.req = list_first_entry(&xb_write_list,
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struct xb_req_data, list);
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state.idx = -1;
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state.written = 0;
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}
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if (state.req->state == xb_req_state_aborted)
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goto out_err;
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while (state.idx < state.req->num_vecs) {
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if (state.idx < 0) {
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base = &state.req->msg;
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len = sizeof(state.req->msg);
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} else {
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base = state.req->vec[state.idx].iov_base;
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len = state.req->vec[state.idx].iov_len;
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}
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err = xb_write(base + state.written, len - state.written);
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if (err < 0)
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goto out_err;
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state.written += err;
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if (state.written != len)
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goto out;
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state.idx++;
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state.written = 0;
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}
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list_del(&state.req->list);
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state.req->state = xb_req_state_wait_reply;
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list_add_tail(&state.req->list, &xs_reply_list);
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state.req = NULL;
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out:
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mutex_unlock(&xb_write_mutex);
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return 0;
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out_err:
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state.req->msg.type = XS_ERROR;
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state.req->err = err;
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list_del(&state.req->list);
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if (state.req->state == xb_req_state_aborted)
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kfree(state.req);
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else {
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state.req->state = xb_req_state_got_reply;
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wake_up(&state.req->wq);
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}
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mutex_unlock(&xb_write_mutex);
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state.req = NULL;
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return err;
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}
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static int xb_thread_work(void)
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{
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return xb_data_to_read() || xb_data_to_write();
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}
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static int xenbus_thread(void *unused)
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{
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int err;
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while (!kthread_should_stop()) {
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if (wait_event_interruptible(xb_waitq, xb_thread_work()))
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continue;
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err = process_msg();
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if (err == -ENOMEM)
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schedule();
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else if (err)
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pr_warn_ratelimited("error %d while reading message\n",
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err);
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err = process_writes();
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if (err)
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pr_warn_ratelimited("error %d while writing message\n",
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err);
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}
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xenbus_task = NULL;
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return 0;
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}
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/**
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* xb_init_comms - Set up interrupt handler off store event channel.
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*/
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int xb_init_comms(void)
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{
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struct xenstore_domain_interface *intf = xen_store_interface;
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if (intf->req_prod != intf->req_cons)
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pr_err("request ring is not quiescent (%08x:%08x)!\n",
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intf->req_cons, intf->req_prod);
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if (intf->rsp_prod != intf->rsp_cons) {
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pr_warn("response ring is not quiescent (%08x:%08x): fixing up\n",
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intf->rsp_cons, intf->rsp_prod);
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/* breaks kdump */
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if (!reset_devices)
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intf->rsp_cons = intf->rsp_prod;
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}
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if (xenbus_irq) {
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/* Already have an irq; assume we're resuming */
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rebind_evtchn_irq(xen_store_evtchn, xenbus_irq);
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} else {
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int err;
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err = bind_evtchn_to_irqhandler(xen_store_evtchn, wake_waiting,
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0, "xenbus", &xb_waitq);
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if (err < 0) {
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pr_err("request irq failed %i\n", err);
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return err;
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}
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xenbus_irq = err;
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if (!xenbus_task) {
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xenbus_task = kthread_run(xenbus_thread, NULL,
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"xenbus");
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if (IS_ERR(xenbus_task))
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return PTR_ERR(xenbus_task);
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}
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}
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return 0;
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}
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void xb_deinit_comms(void)
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{
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unbind_from_irqhandler(xenbus_irq, &xb_waitq);
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xenbus_irq = 0;
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}
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