[PATCH 4/7] drm/xe: Relax runtime pm protection around VM

[Rodrigo Vivi]

In the regular use case scenario, user space will create a
VM, and keep it alive for the entire duration of its workload.

For the regular desktop cases, it means that the VM
is alive even on idle scenarios where display goes off. This
is unacceptable since this would entirely block runtime PM
indefinitely, blocking deeper Package-C state. This would be
a waste drainage of power.

Limit the VM protection solely for long-running workloads that
are not protected by display cases nor by the scheduler
references. By design, run_job for long-running workloads
returns NULL and the scheduler drops all the references of it,
hence protecting the VM for this case is necessary.

This indeed opens up a risk of use case without display, and
without long-running workload, where memory might be mapped
and accessed with direct read and write operations without
any gpu execution involved. Because of this, extra protection
for the special vm_op access callback.

In the ideal case of the mmapped scenario of vm_ops, we would
also get references in the 'open' and 'mmap' callbacks, and
put it back on the 'close' callback, for a balanced case.
However, this would also block the regular desktop case.

v2: Update commit message to a more imperative language and to
    reflect why the VM protection is really needed.
    Also add a comment in the code to let the reason visbible.

Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
Cc: Lucas De Marchi <lucas.demarchi at intel.com>
Cc: Matthew Brost <matthew.brost at intel.com>
Cc: Francois Dugast <francois.dugast at intel.com>
Acked-by: Matthew Brost <matthew.brost at intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
---
 drivers/gpu/drm/xe/xe_bo.c | 17 ++++++++++++++++-
 drivers/gpu/drm/xe/xe_vm.c | 12 +++++++++---
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
index 03f7fe7acf8c..7980efe139ed 100644
--- a/drivers/gpu/drm/xe/xe_bo.c
+++ b/drivers/gpu/drm/xe/xe_bo.c
@@ -1171,11 +1171,26 @@ static vm_fault_t xe_gem_fault(struct vm_fault *vmf)
 	return ret;
 }
 
+static int xe_vm_access(struct vm_area_struct *vma, unsigned long addr,
+			void *buf, int len, int write)
+{
+	struct ttm_buffer_object *tbo = vma->vm_private_data;
+	struct drm_device *ddev = tbo->base.dev;
+	struct xe_device *xe = to_xe_device(ddev);
+	int ret;
+
+	xe_pm_runtime_get(xe);
+	ret = ttm_bo_vm_access(vma, addr, buf, len, write);
+	xe_pm_runtime_put(xe);
+
+	return ret;
+}
+
 static const struct vm_operations_struct xe_gem_vm_ops = {
 	.fault = xe_gem_fault,
 	.open = ttm_bo_vm_open,
 	.close = ttm_bo_vm_close,
-	.access = ttm_bo_vm_access
+	.access = xe_vm_access
 };
 
 static const struct drm_gem_object_funcs xe_gem_object_funcs = {
diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
index d17192c8b7de..f2915741fe16 100644
--- a/drivers/gpu/drm/xe/xe_vm.c
+++ b/drivers/gpu/drm/xe/xe_vm.c
@@ -1347,7 +1347,13 @@ struct xe_vm *xe_vm_create(struct xe_device *xe, u32 flags)
 
 	vm->pt_ops = &xelp_pt_ops;
 
-	if (!(flags & XE_VM_FLAG_MIGRATION))
+	/*
+	 * Long-running workloads are not protected by the scheduler references.
+	 * By design, run_job for long-running workloads returns NULL and the
+	 * scheduler drops all the references of it, hence protecting the VM
+	 * for this case is necessary.
+	 */
+	if (flags & XE_VM_FLAG_LR_MODE)
 		xe_pm_runtime_get_noresume(xe);
 
 	vm_resv_obj = drm_gpuvm_resv_object_alloc(&xe->drm);
@@ -1457,7 +1463,7 @@ struct xe_vm *xe_vm_create(struct xe_device *xe, u32 flags)
 	for_each_tile(tile, xe, id)
 		xe_range_fence_tree_fini(&vm->rftree[id]);
 	kfree(vm);
-	if (!(flags & XE_VM_FLAG_MIGRATION))
+	if (flags & XE_VM_FLAG_LR_MODE)
 		xe_pm_runtime_put(xe);
 	return ERR_PTR(err);
 }
@@ -1592,7 +1598,7 @@ static void vm_destroy_work_func(struct work_struct *w)
 
 	mutex_destroy(&vm->snap_mutex);
 
-	if (!(vm->flags & XE_VM_FLAG_MIGRATION))
+	if (vm->flags & XE_VM_FLAG_LR_MODE)
 		xe_pm_runtime_put(xe);
 
 	for_each_tile(tile, xe, id)
-- 
2.44.0