1 files changed, 21 insertions, 0 deletions

diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c
index 131dec04794e..48220e129f85 100644
--- a/drivers/xen/xenbus/xenbus_xs.c
+++ b/drivers/xen/xenbus/xenbus_xs.c
@@ -48,6 +48,7 @@
 #include <xen/xenbus.h>
 #include <xen/xen.h>
 #include "xenbus_comms.h"
+#include <asm/xen/hypervisor.h>
 
 struct xs_stored_msg {
         struct list_head list;
@@ -618,7 +619,24 @@ static struct xenbus_watch *find_watch(const char *token)
 
         return NULL;
 }
+/*
+ * Certain older XenBus toolstack cannot handle reading values that are
+ * not populated. Some Xen 3.4 installation are incapable of doing this
+ * so if we are running on anything older than 4 do not attempt to read
+ * control/platform-feature-xs_reset_watches.
+ */
+static bool xen_strict_xenbus_quirk()
+{
+        uint32_t eax, ebx, ecx, edx, base;
+
+        base = xen_cpuid_base();
+        cpuid(base + 1, &eax, &ebx, &ecx, &edx);
 
+        if ((eax >> 16) < 4)
+                return true;
+        return false;
+
+}
 static void xs_reset_watches(void)
 {
         int err, supported = 0;
@@ -626,6 +644,9 @@ static void xs_reset_watches(void)
         if (!xen_hvm_domain() || xen_initial_domain())
                 return;
 
+        if (xen_strict_xenbus_quirk())
+                return;
+
         err = xenbus_scanf(XBT_NIL, "control",
                         "platform-feature-xs_reset_watches", "%d", &supported);
         if (err != 1 || !supported)