[PATCH v2 1/1] 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 in case of kexec/kdump. EVTCHNOP_reset looks suitable
for this purpose. However control blocks for vcpus and event array need
cleanup when FIFO ABI is being used.

With this change a guest can simply do EVTCHNOP_reset before kexec in
both 2-level and FIFO cases. It is also important to perform store/console
channel remapping after such call.

The issue can also be solved by introducing a new EVTCHNOP operation but
it seems that EVTCHNOP_reset can be reused.

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

Changes from v1:
- Change EVTCHNOP_reset behavior when it is being called by the guest
  with DOMID_SELF only [Andrew Cooper, Jan Beulich].
- Do not skip interdomain store/console channels, let the guest rebind
  them [David Vrabel].
- Do evtchn_2l_init() after evtchn_fifo_destroy() so the guest can
  perform e.g. EVTCHNOP_bind_interdomain operations after EVTCHNOP_reset.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 xen/common/event_channel.c | 11 +++++++++++
 xen/common/event_fifo.c    |  1 +
 2 files changed, 12 insertions(+)

diff --git a/xen/common/event_channel.c b/xen/common/event_channel.c
index db952af..0dad08d 100644
--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -957,6 +957,17 @@ static long evtchn_reset(evtchn_reset_t *r)
     for ( i = 0; port_is_valid(d, i); i++ )
         (void)__evtchn_close(d, i);
 
+    if ( (d == current->domain) && d->evtchn_fifo )
+    {
+        /*
+         * Guest domain called EVTCHNOP_reset with DOMID_SELF, destroying
+         * FIFO event array and control blocks, resetting evtchn_port_ops to
+         * evtchn_port_ops_2l.
+         */
+        evtchn_fifo_destroy(d);
+        evtchn_2l_init(d);
+    }
+
     rc = 0;
 
 out:
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