Rendezvous selected cpus in softirq (stop_machine).

This is similar to stop_machine_run stub from Linux, to pull
selected cpus in rendezvous point and the do some batch work
under a safe environment. Current one usage is from S3 path,
where individual cpu is pulled down with related online
footprints being cleared. It's dangerous to have other cpus
checking clobbered data structure in the middle, such as
cpu_online_map, cpu_sibling_map, etc.

Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>

1 files changed, 168 insertions, 0 deletions

diff --git a/xen/common/stop_machine.c b/xen/common/stop_machine.c
new file mode 100644
index 0000000000..b109167ef7
--- /dev/null
+++ b/xen/common/stop_machine.c
@@ -0,0 +1,168 @@
+/******************************************************************************
+ * common/stop_machine.c
+ *
+ * Facilities to put whole machine in a safe 'stop' state
+ *
+ * Copyright 2005 Rusty Russell rusty@rustcorp.com.au IBM Corporation
+ * Copyright 2008 Kevin Tian <kevin.tian@intel.com>, 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.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
+ * Place - Suite 330, Boston, MA 02111-1307 USA.
+ */
+
+#include <xen/config.h>
+#include <xen/init.h>
+#include <xen/spinlock.h>
+#include <asm/smp.h>
+#include <asm/current.h>
+#include <xen/softirq.h>
+#include <asm/processor.h>
+#include <xen/errno.h>
+
+enum stopmachine_state {
+    STOPMACHINE_START,
+    STOPMACHINE_PREPARE,
+    STOPMACHINE_DISABLE_IRQ,
+    STOPMACHINE_INVOKE,
+    STOPMACHINE_EXIT
+};
+
+struct stopmachine_data {
+    unsigned int nr_cpus;
+
+    enum stopmachine_state state;
+    atomic_t done;
+
+    unsigned int fn_cpu;
+    int fn_result;
+    int (*fn)(void *);
+    void *fn_data;
+};
+
+static struct stopmachine_data stopmachine_data;
+static DEFINE_SPINLOCK(stopmachine_lock);
+
+static void stopmachine_set_state(enum stopmachine_state state)
+{
+    atomic_set(&stopmachine_data.done, 0);
+    smp_wmb();
+    stopmachine_data.state = state;
+    while ( atomic_read(&stopmachine_data.done) != stopmachine_data.nr_cpus )
+        cpu_relax();
+}
+
+int __stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
+{
+    cpumask_t allbutself;
+    unsigned int i, nr_cpus;
+    int ret;
+
+    BUG_ON(!local_irq_is_enabled());
+
+    allbutself = cpu_online_map;
+    cpu_clear(smp_processor_id(), allbutself);
+    nr_cpus = cpus_weight(allbutself);
+
+    if ( nr_cpus == 0 )
+    {
+        BUG_ON(cpu != smp_processor_id());
+        return (*fn)(data);
+    }
+
+    /* Note: We shouldn't spin on lock when it's held by others since others
+     * is expecting this cpus to enter softirq context. Or else deadlock
+     * is caused.
+     */
+    if ( !spin_trylock(&stopmachine_lock) )
+        return -EBUSY;
+
+    stopmachine_data.fn = fn;
+    stopmachine_data.fn_data = data;
+    stopmachine_data.nr_cpus = nr_cpus;
+    stopmachine_data.fn_cpu = cpu;
+    atomic_set(&stopmachine_data.done, 0);
+    stopmachine_data.state = STOPMACHINE_START;
+
+    smp_wmb();
+
+    for_each_cpu_mask ( i, allbutself )
+        cpu_raise_softirq(i, STOPMACHINE_SOFTIRQ);
+
+    stopmachine_set_state(STOPMACHINE_PREPARE);
+
+    local_irq_disable();
+    stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
+
+    if ( cpu == smp_processor_id() )
+        stopmachine_data.fn_result = (*fn)(data);
+    stopmachine_set_state(STOPMACHINE_INVOKE);
+    ret = stopmachine_data.fn_result;
+
+    stopmachine_set_state(STOPMACHINE_EXIT);
+    local_irq_enable();
+
+    spin_unlock(&stopmachine_lock);
+
+    return ret;
+}
+
+int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
+{
+    int ret;
+
+    lock_cpu_hotplug();
+    ret = __stop_machine_run(fn, data, cpu);
+    unlock_cpu_hotplug();
+
+    return ret;
+}
+
+static void stopmachine_softirq(void)
+{
+    enum stopmachine_state state = STOPMACHINE_START;
+
+    smp_mb();
+
+    while ( state != STOPMACHINE_EXIT )
+    {
+        while ( stopmachine_data.state == state )
+            cpu_relax();
+
+        state = stopmachine_data.state;
+        switch ( state )
+        {
+        case STOPMACHINE_DISABLE_IRQ:
+            local_irq_disable();
+            break;
+        case STOPMACHINE_INVOKE:
+            if ( stopmachine_data.fn_cpu == smp_processor_id() )
+                stopmachine_data.fn_result =
+                    stopmachine_data.fn(stopmachine_data.fn_data);
+            break;
+        default:
+            break;
+        }
+
+        smp_mb();
+        atomic_inc(&stopmachine_data.done);
+    }
+
+    local_irq_enable();
+}
+
+static int __init cpu_stopmachine_init(void)
+{
+    open_softirq(STOPMACHINE_SOFTIRQ, stopmachine_softirq);
+    return 0;
+}
+__initcall(cpu_stopmachine_init);