[PATCH v2 3/7] drm/panthor: Explicit expansion of locked VM region

[Ketil Johnsen]

Currently the panthor_vm_lock_region() function will implicitly expand
an already locked VM region. This can be problematic because the caller
do not reliably know if it needs to call panthor_vm_unlock_region()
or not.

Worth noting, there is currently no known issues with this as the code
is written today.

This change introduces panthor_vm_expand_region() which will only work
if there is already a locked VM region. This again means that the
original lock and unlock functions can work as a pair. This pairing is
needed for subsequent protected memory changes.

Signed-off-by: Ketil Johnsen <ketil.johnsen@xxxxxxx>
---
 drivers/gpu/drm/panthor/panthor_mmu.c | 87 +++++++++++++++++++--------
 1 file changed, 62 insertions(+), 25 deletions(-)

diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
index 1f6b9242279c2..b82b01013611c 100644
--- a/drivers/gpu/drm/panthor/panthor_mmu.c
+++ b/drivers/gpu/drm/panthor/panthor_mmu.c
@@ -1774,20 +1774,49 @@ static const char *access_type_name(struct panthor_device *ptdev,
 	}
 }
 
+static int panthor_vm_apply_as_lock(struct panthor_vm *vm, u64 region)
+{
+	struct panthor_device *ptdev = vm->ptdev;
+
+	lockdep_assert_held(&ptdev->mmu->as.slots_lock);
+
+	gpu_write64(ptdev->mmu->iomem, AS_LOCKADDR(vm->as.id), region);
+	return as_send_cmd_and_wait(ptdev, vm->as.id, AS_COMMAND_LOCK);
+}
+
 static int panthor_vm_lock_region(struct panthor_vm *vm, u64 start, u64 size)
 {
 	struct panthor_device *ptdev = vm->ptdev;
 	int ret = 0;
 
-	/* sm_step_remap() can call panthor_vm_lock_region() to account for
-	 * the wider unmap needed when doing a partial huge page unamp. We
-	 * need to ignore the lock if it's already part of the locked region.
-	 */
-	if (start >= vm->locked_region.start &&
-	    start + size <= vm->locked_region.start + vm->locked_region.size)
-		return 0;
+	if (drm_WARN_ON(&ptdev->base, vm->locked_region.size))
+		return -EINVAL;
+
+	mutex_lock(&ptdev->mmu->as.slots_lock);
+	if (vm->as.id >= 0 && size) {
+		u64 region = pack_region_range(ptdev, &start, &size);
+
+		ret = panthor_vm_apply_as_lock(vm, region);
+	}
 
-	/* sm_step_remap() may need a locked region that isn't a strict superset
+	if (!ret) {
+		vm->locked_region.start = start;
+		vm->locked_region.size = size;
+	}
+	mutex_unlock(&ptdev->mmu->as.slots_lock);
+
+	return ret;
+}
+
+static int panthor_vm_expand_locked_region(struct panthor_vm *vm,
+					   u64 start, u64 size)
+{
+	struct panthor_device *ptdev = vm->ptdev;
+	u64 end;
+	int ret = 0;
+
+	/* This function is here to handle the following case:
+	 * sm_step_remap() may need a locked region that isn't a strict superset
 	 * of the original one because of having to extend unmap boundaries beyond
 	 * it to deal with partial unmaps of transparent huge pages. What we want
 	 * in those cases is to lock the union of both regions. The new region must
@@ -1795,25 +1824,30 @@ static int panthor_vm_lock_region(struct panthor_vm *vm, u64 start, u64 size)
 	 * boundaries in a remap operation can only shift up or down respectively,
 	 * but never otherwise.
 	 */
-	if (vm->locked_region.size) {
-		u64 end = max(vm->locked_region.start + vm->locked_region.size,
-			      start + size);
 
-		drm_WARN_ON_ONCE(&vm->ptdev->base, (start + size <= vm->locked_region.start) ||
-				 (start >= vm->locked_region.start + vm->locked_region.size));
+	/* This function can only expand an already locked region */
+	if (drm_WARN_ON(&ptdev->base, !vm->locked_region.size))
+		return -EINVAL;
+
+	/* Early out if requested range is already locked */
+	if (start >= vm->locked_region.start &&
+	    start + size <= vm->locked_region.start + vm->locked_region.size)
+		return 0;
 
-		start = min(start, vm->locked_region.start);
-		size = end - start;
-	}
+	end = max(vm->locked_region.start + vm->locked_region.size,
+		  start + size);
+
+	drm_WARN_ON_ONCE(&ptdev->base, (start + size <= vm->locked_region.start) ||
+			 (start >= vm->locked_region.start + vm->locked_region.size));
+
+	start = min(start, vm->locked_region.start);
+	size = end - start;
 
 	mutex_lock(&ptdev->mmu->as.slots_lock);
 	if (vm->as.id >= 0 && size) {
-		/* Lock the region that needs to be updated */
-		gpu_write64(ptdev->mmu->iomem, AS_LOCKADDR(vm->as.id),
-			    pack_region_range(ptdev, &start, &size));
+		u64 region = pack_region_range(ptdev, &start, &size);
 
-		/* If the lock succeeded, update the locked_region info. */
-		ret = as_send_cmd_and_wait(ptdev, vm->as.id, AS_COMMAND_LOCK);
+		ret = panthor_vm_apply_as_lock(vm, region);
 	}
 
 	if (!ret) {
@@ -2367,11 +2401,14 @@ static int panthor_gpuva_sm_step_remap(struct drm_gpuva_op *op,
 		 */
 		unmap_hugepage_align(&op->remap, &unmap_start, &unmap_range);
 
-		/* If the range changed, we might have to lock a wider region to guarantee
-		 * atomicity. panthor_vm_lock_region() bails out early if the new region
-		 * is already part of the locked region, so no need to do this check here.
+		/* If the range changed, we might have to lock a wider region to
+		 * guarantee atomicity.
 		 */
-		panthor_vm_lock_region(vm, unmap_start, unmap_range);
+		ret = panthor_vm_expand_locked_region(vm, unmap_start,
+						      unmap_range);
+		if (ret)
+			return ret;
+
 		panthor_vm_unmap_pages(vm, unmap_start, unmap_range);
 	}
 
-- 
2.43.0