[PATCH v2 7/7] mm: update lazy_mmu documentation

[Kevin Brodsky <kevin.brodsky@arm.com>]

We now support nested lazy_mmu sections on all architectures
implementing the API. Update the API comment accordingly.

Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
---
 include/linux/pgtable.h | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index df0eb898b3fc..85cd1fdb914f 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -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;
-- 
2.47.0