drm/amdkfd: simplify drain retry fault

unmap range always increase atomic svms->drain_pagefaults to simplify
both parent range and child range unmap, page fault handle ignores the
retry fault if svms->drain_pagefaults is set to speed up interrupt
handling. svm_range_drain_retry_fault restart draining if another
range unmap from cpu.
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdkfd/kfd_priv.h

@@ -766,7 +766,7 @@ struct svm_range_list {
 	struct list_head		deferred_range_list;
 	spinlock_t			deferred_list_lock;
 	atomic_t			evicted_ranges;
-	bool				drain_pagefaults;
+	atomic_t			drain_pagefaults;
 	struct delayed_work		restore_work;
 	DECLARE_BITMAP(bitmap_supported, MAX_GPU_INSTANCE);
 	struct task_struct 		*faulting_task;

drivers/gpu/drm/amd/amdkfd/kfd_svm.c

@@ -1968,10 +1968,16 @@ static void svm_range_drain_retry_fault(struct svm_range_list *svms)
 	struct kfd_process_device *pdd;
 	struct amdgpu_device *adev;
 	struct kfd_process *p;
+	int drain;
 	uint32_t i;
 
 	p = container_of(svms, struct kfd_process, svms);
 
+restart:
+	drain = atomic_read(&svms->drain_pagefaults);
+	if (!drain)
+		return;
+
 	for_each_set_bit(i, svms->bitmap_supported, p->n_pdds) {
 		pdd = p->pdds[i];
 		if (!pdd)
@@ -1983,6 +1989,8 @@ static void svm_range_drain_retry_fault(struct svm_range_list *svms)
 		amdgpu_ih_wait_on_checkpoint_process(adev, &adev->irq.ih1);
 		pr_debug("drain retry fault gpu %d svms 0x%p done\n", i, svms);
 	}
+	if (atomic_cmpxchg(&svms->drain_pagefaults, drain, 0) != drain)
+		goto restart;
 }
 
 static void svm_range_deferred_list_work(struct work_struct *work)
@@ -2008,8 +2016,7 @@ static void svm_range_deferred_list_work(struct work_struct *work)
 	/* Checking for the need to drain retry faults must be inside
 	 * mmap write lock to serialize with munmap notifiers.
 	 */
-	if (unlikely(READ_ONCE(svms->drain_pagefaults))) {
-		WRITE_ONCE(svms->drain_pagefaults, false);
+	if (unlikely(atomic_read(&svms->drain_pagefaults))) {
 		mmap_write_unlock(mm);
 		svm_range_drain_retry_fault(svms);
 		goto retry;
@@ -2056,12 +2063,6 @@ svm_range_add_list_work(struct svm_range_list *svms, struct svm_range *prange,
 			struct mm_struct *mm, enum svm_work_list_ops op)
 {
 	spin_lock(&svms->deferred_list_lock);
-	/* Make sure pending page faults are drained in the deferred worker
-	 * before the range is freed to avoid straggler interrupts on
-	 * unmapped memory causing "phantom faults".
-	 */
-	if (op == SVM_OP_UNMAP_RANGE)
-		svms->drain_pagefaults = true;
 	/* if prange is on the deferred list */
 	if (!list_empty(&prange->deferred_list)) {
 		pr_debug("update exist prange 0x%p work op %d\n", prange, op);
@@ -2140,6 +2141,12 @@ svm_range_unmap_from_cpu(struct mm_struct *mm, struct svm_range *prange,
 	pr_debug("svms 0x%p prange 0x%p [0x%lx 0x%lx] [0x%lx 0x%lx]\n", svms,
 		 prange, prange->start, prange->last, start, last);
 
+	/* Make sure pending page faults are drained in the deferred worker
+	 * before the range is freed to avoid straggler interrupts on
+	 * unmapped memory causing "phantom faults".
+	 */
+	atomic_inc(&svms->drain_pagefaults);
+
 	unmap_parent = start <= prange->start && last >= prange->last;
 
 	list_for_each_entry(pchild, &prange->child_list, child_list) {
@@ -2605,6 +2612,11 @@ svm_range_restore_pages(struct amdgpu_device *adev, unsigned int pasid,
 
 	pr_debug("restoring svms 0x%p fault address 0x%llx\n", svms, addr);
 
+	if (atomic_read(&svms->drain_pagefaults)) {
+		pr_debug("draining retry fault, drop fault 0x%llx\n", addr);
+		goto out;
+	}
+
 	/* p->lead_thread is available as kfd_process_wq_release flush the work
 	 * before releasing task ref.
 	 */
@@ -2751,6 +2763,7 @@ void svm_range_list_fini(struct kfd_process *p)
 	 * Ensure no retry fault comes in afterwards, as page fault handler will
 	 * not find kfd process and take mm lock to recover fault.
 	 */
+	atomic_inc(&p->svms.drain_pagefaults);
 	svm_range_drain_retry_fault(&p->svms);
 
 
@@ -2774,6 +2787,7 @@ int svm_range_list_init(struct kfd_process *p)
 	mutex_init(&svms->lock);
 	INIT_LIST_HEAD(&svms->list);
 	atomic_set(&svms->evicted_ranges, 0);
+	atomic_set(&svms->drain_pagefaults, 0);
 	INIT_DELAYED_WORK(&svms->restore_work, svm_range_restore_work);
 	INIT_WORK(&svms->deferred_list_work, svm_range_deferred_list_work);
 	INIT_LIST_HEAD(&svms->deferred_range_list);