@@ -228,8 +228,18 @@ static inline int pmd_dirty(pmd_t pmd)
  * of the lazy mode. So the implementation must assume preemption may be enabled
  * and cpu migration is possible; it must take steps to be robust against this.
  * (In practice, for user PTE updates, the appropriate page table lock(s) are
- * held, but for kernel PTE updates, no lock is held). Nesting is not permitted
- * and the mode cannot be used in interrupt context.
+ * held, but for kernel PTE updates, no lock is held). The mode cannot be used
+ * in interrupt context.
+ *
+ * Calls may be nested: an arch_{enter,leave}_lazy_mmu_mode() pair may be called
+ * while the lazy MMU mode has already been enabled. An implementation should
+ * handle this using the state returned by enter() and taken by the matching
+ * leave() call; the LAZY_MMU_{DEFAULT,NESTED} flags can be used to indicate
+ * whether this enter/leave pair is nested inside another or not. (It is up to
+ * the implementation to track whether the lazy MMU mode is enabled at any point
+ * in time.) The expectation is that leave() will flush any batched state
+ * unconditionally, but only leave the lazy MMU mode if the passed state is not
+ * LAZY_MMU_NESTED.
  */
 #ifndef __HAVE_ARCH_ENTER_LAZY_MMU_MODE
 typedef int lazy_mmu_state_t;