[PATCH 03/14] mm/hmm: HMM should have a callback before MM is destroyed v2

[jglisse]

From: Ralph Campbell <rcampb...@nvidia.com>

The hmm_mirror_register() function registers a callback for when
the CPU pagetable is modified. Normally, the device driver will
call hmm_mirror_unregister() when the process using the device is
finished. However, if the process exits uncleanly, the struct_mm
can be destroyed with no warning to the device driver.

Changed since v1:
  - dropped VM_BUG_ON()
  - cc stable

Signed-off-by: Ralph Campbell <rcampb...@nvidia.com>
Signed-off-by: Jérôme Glisse <jgli...@redhat.com>
Cc: sta...@vger.kernel.org
Cc: Evgeny Baskakov <ebaska...@nvidia.com>
Cc: Mark Hairgrove <mhairgr...@nvidia.com>
Cc: John Hubbard <jhubb...@nvidia.com>
---
 include/linux/hmm.h | 10 ++++++++++
 mm/hmm.c            | 18 +++++++++++++++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index ef6044d08cc5..61b0e1c05ee1 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -218,6 +218,16 @@ enum hmm_update_type {
  * @update: callback to update range on a device
  */
 struct hmm_mirror_ops {
+       /* release() - release hmm_mirror
+        *
+        * @mirror: pointer to struct hmm_mirror
+        *
+        * This is called when the mm_struct is being released.
+        * The callback should make sure no references to the mirror occur
+        * after the callback returns.
+        */
+       void (*release)(struct hmm_mirror *mirror);
+
        /* sync_cpu_device_pagetables() - synchronize page tables
         *
         * @mirror: pointer to struct hmm_mirror
diff --git a/mm/hmm.c b/mm/hmm.c
index 320545b98ff5..6088fa6ed137 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -160,6 +160,21 @@ static void hmm_invalidate_range(struct hmm *hmm,
        up_read(&hmm->mirrors_sem);
 }
 
+static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+       struct hmm *hmm = mm->hmm;
+       struct hmm_mirror *mirror;
+       struct hmm_mirror *mirror_next;
+
+       down_write(&hmm->mirrors_sem);
+       list_for_each_entry_safe(mirror, mirror_next, &hmm->mirrors, list) {
+               list_del_init(&mirror->list);
+               if (mirror->ops->release)
+                       mirror->ops->release(mirror);
+       }
+       up_write(&hmm->mirrors_sem);
+}
+
 static void hmm_invalidate_range_start(struct mmu_notifier *mn,
                                       struct mm_struct *mm,
                                       unsigned long start,
@@ -185,6 +200,7 @@ static void hmm_invalidate_range_end(struct mmu_notifier 
*mn,
 }
 
 static const struct mmu_notifier_ops hmm_mmu_notifier_ops = {
+       .release                = hmm_release,
        .invalidate_range_start = hmm_invalidate_range_start,
        .invalidate_range_end   = hmm_invalidate_range_end,
 };
@@ -230,7 +246,7 @@ void hmm_mirror_unregister(struct hmm_mirror *mirror)
        struct hmm *hmm = mirror->hmm;
 
        down_write(&hmm->mirrors_sem);
-       list_del(&mirror->list);
+       list_del_init(&mirror->list);
        up_write(&hmm->mirrors_sem);
 }
 EXPORT_SYMBOL(hmm_mirror_unregister);
-- 
2.14.3