[PATCH v2] drm/panthor: Evict groups before VM termination

[Ketil Johnsen <ketil.johnsen@arm.com>]

Ensure all related groups are evicted and suspended before VM
destruction takes place.

This fixes an issue where panthor_vm_destroy() destroys and unmaps the
heap context while there are still on slot groups using this.
The FW will do a write out to the heap context when a CSG (group) is
suspended, so a premature unmap of the heap context will cause a
GPU page fault.
This page fault is quite harmless, and do not affect the continued
operation of the GPU.

Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Co-developed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Ketil Johnsen <ketil.johnsen@arm.com>
---
Changes in v2:
- Removed check for ptdev->scheduler
- R-b from Boris
- Link to v1: https://lore.kernel.org/all/20251218162644.828495-1-ketil.johnsen@arm.com/
---
 drivers/gpu/drm/panthor/panthor_mmu.c   |  4 ++++
 drivers/gpu/drm/panthor/panthor_sched.c | 14 ++++++++++++++
 drivers/gpu/drm/panthor/panthor_sched.h |  1 +
 3 files changed, 19 insertions(+)

diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
index 74230f7199121..0e4b301a9c70e 100644
--- a/drivers/gpu/drm/panthor/panthor_mmu.c
+++ b/drivers/gpu/drm/panthor/panthor_mmu.c
@@ -1537,6 +1537,10 @@ static void panthor_vm_destroy(struct panthor_vm *vm)
 
 	vm->destroyed = true;
 
+	/* Tell scheduler to stop all GPU work related to this VM */
+	if (refcount_read(&vm->as.active_cnt) > 0)
+		panthor_sched_prepare_for_vm_destruction(vm->ptdev);
+
 	mutex_lock(&vm->heaps.lock);
 	panthor_heap_pool_destroy(vm->heaps.pool);
 	vm->heaps.pool = NULL;
diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
index f680edcd40aad..a40ac94e5e989 100644
--- a/drivers/gpu/drm/panthor/panthor_sched.c
+++ b/drivers/gpu/drm/panthor/panthor_sched.c
@@ -2930,6 +2930,20 @@ void panthor_sched_report_mmu_fault(struct panthor_device *ptdev)
 		sched_queue_delayed_work(ptdev->scheduler, tick, 0);
 }
 
+void panthor_sched_prepare_for_vm_destruction(struct panthor_device *ptdev)
+{
+	/* FW can write out internal state, like the heap context, during CSG
+	 * suspend. It is therefore important that the scheduler has fully
+	 * evicted any pending and related groups before VM destruction can
+	 * safely continue. Failure to do so can lead to GPU page faults.
+	 * A controlled termination of a Panthor instance involves destroying
+	 * the group(s) before the VM. This means any relevant group eviction
+	 * has already been initiated by this point, and we just need to
+	 * ensure that any pending tick_work() has been completed.
+	 */
+	flush_work(&ptdev->scheduler->tick_work.work);
+}
+
 void panthor_sched_resume(struct panthor_device *ptdev)
 {
 	/* Force a tick to re-evaluate after a resume. */
diff --git a/drivers/gpu/drm/panthor/panthor_sched.h b/drivers/gpu/drm/panthor/panthor_sched.h
index f4a475aa34c0a..9a8692de8aded 100644
--- a/drivers/gpu/drm/panthor/panthor_sched.h
+++ b/drivers/gpu/drm/panthor/panthor_sched.h
@@ -50,6 +50,7 @@ void panthor_sched_suspend(struct panthor_device *ptdev);
 void panthor_sched_resume(struct panthor_device *ptdev);
 
 void panthor_sched_report_mmu_fault(struct panthor_device *ptdev);
+void panthor_sched_prepare_for_vm_destruction(struct panthor_device *ptdev);
 void panthor_sched_report_fw_events(struct panthor_device *ptdev, u32 events);
 
 void panthor_fdinfo_gather_group_samples(struct panthor_file *pfile);
-- 
2.43.0