A patch of grotesque beauty. Some gem comments.
+ * Run a transaction which would only trigger xabort if the condition
+ * is true. This xabort is counted by the PMU and will trigger an
+ * interrupt. The conditional move prevents speculative evaluation of
+ * the condition. The branch would not mistakenly be mispredicted later
+ * to run xabort again, since we run IBPB in the nmi handler.