xen/pv-on-hvm kexec: shutdown watches from old kernel

Add xs_reset_watches function to shutdown watches from old kernel after
kexec boot.  The old kernel does not unregister all watches in the
shutdown path.  They are still active, the double registration can not
be detected by the new kernel.  When the watches fire, unexpected events
will arrive and the xenwatch thread will crash (jumps to NULL).  An
orderly reboot of a hvm guest will destroy the entire guest with all its
resources (including the watches) before it is rebuilt from scratch, so
the missing unregister is not an issue in that case.

With this change the xenstored is instructed to wipe all active watches
for the guest.  However, a patch for xenstored is required so that it
accepts the XS_RESET_WATCHES request from a client (see changeset
23839:42a45baf037d in xen-unstable.hg). Without the patch for xenstored
the registration of watches will fail and some features of a PVonHVM
guest are not available. The guest is still able to boot, but repeated
kexec boots will fail.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c
index d1c217b23a428ee5139727860243aec9a40ff8e8..bce15cf4a8df1708a5237a12e7223ca56b093e8f 100644 (file)
--- a/drivers/xen/xenbus/xenbus_xs.c
+++ b/drivers/xen/xenbus/xenbus_xs.c
@@ -618,6 +618,23 @@ static struct xenbus_watch *find_watch(const char *token)
        return NULL;
 }
 
+static void xs_reset_watches(void)
+{
+       int err, supported = 0;
+
+       if (!xen_hvm_domain())
+               return;
+
+       err = xenbus_scanf(XBT_NIL, "control",
+                       "platform-feature-xs_reset_watches", "%d", &supported);
+       if (err != 1 || !supported)
+               return;
+
+       err = xs_error(xs_single(XBT_NIL, XS_RESET_WATCHES, "", NULL));
+       if (err && err != -EEXIST)
+               printk(KERN_WARNING "xs_reset_watches failed: %d\n", err);
+}
+
 /* Register callback to watch this node. */
 int register_xenbus_watch(struct xenbus_watch *watch)
 {
@@ -900,5 +917,8 @@ int xs_init(void)
        if (IS_ERR(task))
                return PTR_ERR(task);
 
+       /* shutdown watches for kexec boot */
+       xs_reset_watches();
+
        return 0;
 }

diff --git a/include/xen/interface/io/xs_wire.h b/include/xen/interface/io/xs_wire.h
index 7cdfca24eafbcc4bc9c1a95f192aaaed6aee5a81..794deb07eb534c376930f0f9f34ec9c44c73240c 100644 (file)
--- a/include/xen/interface/io/xs_wire.h
+++ b/include/xen/interface/io/xs_wire.h
@@ -29,7 +29,8 @@ enum xsd_sockmsg_type
     XS_IS_DOMAIN_INTRODUCED,
     XS_RESUME,
     XS_SET_TARGET,
-    XS_RESTRICT
+    XS_RESTRICT,
+    XS_RESET_WATCHES,
 };
 
 #define XS_WRITE_NONE "NONE"