[RFC] mm/hmm: pass mmu_notifier_range to sync_cpu_device_pagetables

[Ralph Campbell]

HMM defines its own struct hmm_update which is passed to the
sync_cpu_device_pagetables() callback function. This is
sufficient when the only action is to invalidate. However,
a device may want to know the reason for the invalidation and
be able to see the new permissions on a range, update device access
rights or range statistics. Since sync_cpu_device_pagetables()
can be called from try_to_unmap(), the mmap_sem may not be held
and find_vma() is not safe to be called.
Pass the struct mmu_notifier_range to sync_cpu_device_pagetables()
to allow the full invalidation information to be used.

Signed-off-by: Ralph Campbell <rcampbell at nvidia.com>
---

I'm sending this out now since we are updating many of the HMM APIs
and I think it will be useful.


 drivers/gpu/drm/nouveau/nouveau_svm.c |  4 ++--
 include/linux/hmm.h                   | 27 ++-------------------------
 mm/hmm.c                              | 13 ++++---------
 3 files changed, 8 insertions(+), 36 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c b/drivers/gpu/drm/nouveau/nouveau_svm.c
index 8c92374afcf2..c34b98fafe2f 100644
--- a/drivers/gpu/drm/nouveau/nouveau_svm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
@@ -252,13 +252,13 @@ nouveau_svmm_invalidate(struct nouveau_svmm *svmm, u64 start, u64 limit)
 
 static int
 nouveau_svmm_sync_cpu_device_pagetables(struct hmm_mirror *mirror,
-					const struct hmm_update *update)
+					const struct mmu_notifier_range *update)
 {
 	struct nouveau_svmm *svmm = container_of(mirror, typeof(*svmm), mirror);
 	unsigned long start = update->start;
 	unsigned long limit = update->end;
 
-	if (!update->blockable)
+	if (!mmu_notifier_range_blockable(update))
 		return -EAGAIN;
 
 	SVMM_DBG(svmm, "invalidate %016lx-%016lx", start, limit);
diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 0fa8ea34ccef..07a2d38fde34 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -377,29 +377,6 @@ static inline uint64_t hmm_pfn_from_pfn(const struct hmm_range *range,
 
 struct hmm_mirror;
 
-/*
- * enum hmm_update_event - type of update
- * @HMM_UPDATE_INVALIDATE: invalidate range (no indication as to why)
- */
-enum hmm_update_event {
-	HMM_UPDATE_INVALIDATE,
-};
-
-/*
- * struct hmm_update - HMM update information for callback
- *
- * @start: virtual start address of the range to update
- * @end: virtual end address of the range to update
- * @event: event triggering the update (what is happening)
- * @blockable: can the callback block/sleep ?
- */
-struct hmm_update {
-	unsigned long start;
-	unsigned long end;
-	enum hmm_update_event event;
-	bool blockable;
-};
-
 /*
  * struct hmm_mirror_ops - HMM mirror device operations callback
  *
@@ -420,7 +397,7 @@ struct hmm_mirror_ops {
 	/* sync_cpu_device_pagetables() - synchronize page tables
 	 *
 	 * @mirror: pointer to struct hmm_mirror
-	 * @update: update information (see struct hmm_update)
+	 * @update: update information (see struct mmu_notifier_range)
 	 * Return: -EAGAIN if update.blockable false and callback need to
 	 *          block, 0 otherwise.
 	 *
@@ -434,7 +411,7 @@ struct hmm_mirror_ops {
 	 * synchronous call.
 	 */
 	int (*sync_cpu_device_pagetables)(struct hmm_mirror *mirror,
-					  const struct hmm_update *update);
+				const struct mmu_notifier_range *update);
 };
 
 /*
diff --git a/mm/hmm.c b/mm/hmm.c
index 9aad3550f2bb..b49a43712554 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -164,7 +164,6 @@ static int hmm_invalidate_range_start(struct mmu_notifier *mn,
 {
 	struct hmm *hmm = container_of(mn, struct hmm, mmu_notifier);
 	struct hmm_mirror *mirror;
-	struct hmm_update update;
 	struct hmm_range *range;
 	unsigned long flags;
 	int ret = 0;
@@ -173,15 +172,10 @@ static int hmm_invalidate_range_start(struct mmu_notifier *mn,
 	if (!kref_get_unless_zero(&hmm->kref))
 		return 0;
 
-	update.start = nrange->start;
-	update.end = nrange->end;
-	update.event = HMM_UPDATE_INVALIDATE;
-	update.blockable = mmu_notifier_range_blockable(nrange);
-
 	spin_lock_irqsave(&hmm->ranges_lock, flags);
 	hmm->notifiers++;
 	list_for_each_entry(range, &hmm->ranges, list) {
-		if (update.end < range->start || update.start >= range->end)
+		if (nrange->end < range->start || nrange->start >= range->end)
 			continue;
 
 		range->valid = false;
@@ -198,9 +192,10 @@ static int hmm_invalidate_range_start(struct mmu_notifier *mn,
 	list_for_each_entry(mirror, &hmm->mirrors, list) {
 		int rc;
 
-		rc = mirror->ops->sync_cpu_device_pagetables(mirror, &update);
+		rc = mirror->ops->sync_cpu_device_pagetables(mirror, nrange);
 		if (rc) {
-			if (WARN_ON(update.blockable || rc != -EAGAIN))
+			if (WARN_ON(mmu_notifier_range_blockable(nrange) ||
+				    rc != -EAGAIN))
 				continue;
 			ret = -EAGAIN;
 			break;
-- 
2.20.1