[PATCH v12 11/29] HMM: add discard range helper (to clear and free resources for a range).

[JÃrÃme Glisse]

A common use case is for device driver to stop caring for a range of
address long before said range is munmapped by userspace program. To
avoid keeping track of such range provide an helper function that will
free HMM resources for a range of address.

NOTE THAT DEVICE DRIVER MUST MAKE SURE THE HARDWARE WILL NO LONGER
ACCESS THE RANGE BECAUSE CALLING THIS HELPER !

Signed-off-by: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
---
 include/linux/hmm.h |  3 +++
 mm/hmm.c            | 24 ++++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index d819ec9..10e1558 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -265,6 +265,9 @@ void hmm_mirror_unregister(struct hmm_mirror *mirror);
 struct hmm_mirror *hmm_mirror_ref(struct hmm_mirror *mirror);
 void hmm_mirror_unref(struct hmm_mirror **mirror);
 int hmm_mirror_fault(struct hmm_mirror *mirror, struct hmm_event *event);
+void hmm_mirror_range_discard(struct hmm_mirror *mirror,
+			      unsigned long start,
+			      unsigned long end);
 
 
 #endif /* CONFIG_HMM */
diff --git a/mm/hmm.c b/mm/hmm.c
index 7b6ba6a..548f0c5 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -921,6 +921,30 @@ out:
 }
 EXPORT_SYMBOL(hmm_mirror_fault);
 
+/* hmm_mirror_range_discard() - discard a range of address.
+ *
+ * @mirror: The mirror struct.
+ * @start: Start address of the range to discard (inclusive).
+ * @end: End address of the range to discard (exclusive).
+ *
+ * Call when device driver want to stop mirroring a range of address and free
+ * any HMM resources associated with that range (including dma mapping if any).
+ *
+ * THIS FUNCTION ASSUME THAT DRIVER ALREADY STOPPED USING THE RANGE OF ADDRESS
+ * AND THUS DO NOT PERFORM ANY SYNCHRONIZATION OR UPDATE WITH THE DRIVER TO
+ * INVALIDATE SAID RANGE.
+ */
+void hmm_mirror_range_discard(struct hmm_mirror *mirror,
+			      unsigned long start,
+			      unsigned long end)
+{
+	struct hmm_event event;
+
+	hmm_event_init(&event, mirror->hmm, start, end, HMM_MUNMAP);
+	hmm_mirror_update_pt(mirror, &event, NULL);
+}
+EXPORT_SYMBOL(hmm_mirror_range_discard);
+
 /* hmm_mirror_register() - register mirror against current process for a device.
  *
  * @mirror: The mirror struct being registered.
-- 
2.4.3