From: Tvrtko Ursulin Date: Tue, 10 Jun 2025 16:42:26 +0000 (+0100) Subject: drm/xe: Make dma-fences compliant with the safe access rules X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6bd90e700b4285e6a7541e00f969cab0d696adde;p=thirdparty%2Fkernel%2Flinux.git drm/xe: Make dma-fences compliant with the safe access rules Xe can free some of the data pointed to by the dma-fences it exports. Most notably the timeline name can get freed if userspace closes the associated submit queue. At the same time the fence could have been exported to a third party (for example a sync_fence fd) which will then cause an use- after-free on subsequent access. To make this safe we need to make the driver compliant with the newly documented dma-fence rules. Driver has to ensure a RCU grace period between signalling a fence and freeing any data pointed to by said fence. For the timeline name we simply make the queue be freed via kfree_rcu and for the shared lock associated with multiple queues we add a RCU grace period before freeing the per GT structure holding the lock. Signed-off-by: Tvrtko Ursulin Reviewed-by: Matthew Brost Acked-by: Lucas De Marchi Signed-off-by: Tvrtko Ursulin Link: https://lore.kernel.org/r/20250610164226.10817-5-tvrtko.ursulin@igalia.com --- diff --git a/drivers/gpu/drm/xe/xe_guc_exec_queue_types.h b/drivers/gpu/drm/xe/xe_guc_exec_queue_types.h index 4c39f01e4f528..a3f421e2adc03 100644 --- a/drivers/gpu/drm/xe/xe_guc_exec_queue_types.h +++ b/drivers/gpu/drm/xe/xe_guc_exec_queue_types.h @@ -20,6 +20,8 @@ struct xe_exec_queue; struct xe_guc_exec_queue { /** @q: Backpointer to parent xe_exec_queue */ struct xe_exec_queue *q; + /** @rcu: For safe freeing of exported dma fences */ + struct rcu_head rcu; /** @sched: GPU scheduler for this xe_exec_queue */ struct xe_gpu_scheduler sched; /** @entity: Scheduler entity for this xe_exec_queue */ diff --git a/drivers/gpu/drm/xe/xe_guc_submit.c b/drivers/gpu/drm/xe/xe_guc_submit.c index 6d84a52b660ac..4a9ada5edbca4 100644 --- a/drivers/gpu/drm/xe/xe_guc_submit.c +++ b/drivers/gpu/drm/xe/xe_guc_submit.c @@ -1285,7 +1285,11 @@ static void __guc_exec_queue_fini_async(struct work_struct *w) xe_sched_entity_fini(&ge->entity); xe_sched_fini(&ge->sched); - kfree(ge); + /* + * RCU free due sched being exported via DRM scheduler fences + * (timeline name). + */ + kfree_rcu(ge, rcu); xe_exec_queue_fini(q); xe_pm_runtime_put(guc_to_xe(guc)); } @@ -1468,6 +1472,7 @@ static int guc_exec_queue_init(struct xe_exec_queue *q) q->guc = ge; ge->q = q; + init_rcu_head(&ge->rcu); init_waitqueue_head(&ge->suspend_wait); for (i = 0; i < MAX_STATIC_MSG_TYPE; ++i) diff --git a/drivers/gpu/drm/xe/xe_hw_fence.c b/drivers/gpu/drm/xe/xe_hw_fence.c index 03eb8c6d16169..b2a0c46dfcd42 100644 --- a/drivers/gpu/drm/xe/xe_hw_fence.c +++ b/drivers/gpu/drm/xe/xe_hw_fence.c @@ -100,6 +100,9 @@ void xe_hw_fence_irq_finish(struct xe_hw_fence_irq *irq) spin_unlock_irqrestore(&irq->lock, flags); dma_fence_end_signalling(tmp); } + + /* Safe release of the irq->lock used in dma_fence_init. */ + synchronize_rcu(); } void xe_hw_fence_irq_run(struct xe_hw_fence_irq *irq)