+ /*
+ * Fix up the exception frame if we're on Xen.
+ * PARAVIRT_ADJUST_EXCEPTION_FRAME is guaranteed to push at most
+ * one value to the stack on native, so it may clobber the rdx
+ * scratch slot, but it won't clobber any of the important
+ * slots past it.
+ *
+ * Xen is a different story, because the Xen frame itself overlaps
+ * the "NMI executing" variable.
+ */