[PATCH] evtchn: make EVTCHNOP_reset suitable for kexec

[Vitaly Kuznetsov <vkuznets@redhat.com>]

It would be nice to allow guests to close all event channels in
ABI-agnostic way on startup. This would allow a guest to perform
full cleanup in case of kexec/kdump. EVTCHNOP_reset looks suitable
for this purpose. However it has two issues:

- current implementation unconditionally closes all event channels
  including store/console channels mapped to Dom0. There is no way
  for a guest to restore these channels after they were closed.

- control blocks for vcpus need cleanup when FIFO ABI is being used.

With this change a guest can simply do EVTCHNOP_reset before its
init in both 2-level and FIFO cases. Unfortunately we'll need to
put something like "xen_version >= 4.5" check before doing it as
if we do it with the old implementation the guest will get stuck.

The issue can also be solved by introducing a new EVTCHNOP
operation but it seems that EVTCHNOP_reset was originally designed
for such reset and it's not being used at this moment.

[The idea was suggested by Ian Campbell and Andrew Cooper]

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 xen/common/event_channel.c | 17 +++++++++++++++--
 xen/common/event_fifo.c    |  1 +
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/xen/common/event_channel.c b/xen/common/event_channel.c
index db952af..46a0ef0 100644
--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -944,6 +944,7 @@ static long evtchn_reset(evtchn_reset_t *r)
 {
     domid_t dom = r->dom;
     struct domain *d;
+    struct evtchn *chn;
     int i, rc;
 
     d = rcu_lock_domain_by_any_id(dom);
@@ -954,8 +955,20 @@ static long evtchn_reset(evtchn_reset_t *r)
     if ( rc )
         goto out;
 
-    for ( i = 0; port_is_valid(d, i); i++ )
-        (void)__evtchn_close(d, i);
+    for ( i = 1; port_is_valid(d, i); i++ )
+    {
+        /*
+         * Leave all interdomain connections to Dom0 untouched as we need to
+         * preserve store/console channels.
+         */
+        chn = evtchn_from_port(d, i);
+        if ( chn->state != ECS_INTERDOMAIN ||
+             chn->u.interdomain.remote_dom->domain_id != 0 )
+            (void)__evtchn_close(d, i);
+    }
+
+    if (d->evtchn_fifo)
+        evtchn_fifo_destroy(d);
 
     rc = 0;
 
diff --git a/xen/common/event_fifo.c b/xen/common/event_fifo.c
index 1fce3f1..51b4ff6 100644
--- a/xen/common/event_fifo.c
+++ b/xen/common/event_fifo.c
@@ -451,6 +451,7 @@ static void cleanup_event_array(struct domain *d)
     for ( i = 0; i < EVTCHN_FIFO_MAX_EVENT_ARRAY_PAGES; i++ )
         unmap_guest_page(d->evtchn_fifo->event_array[i]);
     xfree(d->evtchn_fifo);
+    d->evtchn_fifo = NULL;
 }
 
 static void setup_ports(struct domain *d)
-- 
1.9.3