[PATCH 3/3] drm/amdkfd: simplify drain retry fault

[Philip Yang]

unmap range always set svms->drain_pagefaults flag to simplify both
parent range and child range unmap. Deferred list work takes mmap write
lock to read and clear svms->drain_pagefaults, to serialize with unmap
callback.

Add atomic flag svms->draining_faults, if svms->draining_faults is set,
page fault handle ignore the retry fault, to speed up interrupt handling.

Signed-off-by: Philip Yang <Philip.Yang at amd.com>
---
 drivers/gpu/drm/amd/amdkfd/kfd_priv.h |  1 +
 drivers/gpu/drm/amd/amdkfd/kfd_svm.c  | 24 ++++++++++++++++++------
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_priv.h b/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
index 1d3f012bcd2a..4e4640b731e1 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
@@ -767,6 +767,7 @@ struct svm_range_list {
 	spinlock_t			deferred_list_lock;
 	atomic_t			evicted_ranges;
 	bool				drain_pagefaults;
+	atomic_t			draining_faults;
 	struct delayed_work		restore_work;
 	DECLARE_BITMAP(bitmap_supported, MAX_GPU_INSTANCE);
 	struct task_struct 		*faulting_task;
diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
index 3eb0a9491755..d332462bf9d3 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
@@ -1962,6 +1962,7 @@ void svm_range_drain_retry_fault(struct svm_range_list *svms)
 
 	p = container_of(svms, struct kfd_process, svms);
 
+	atomic_set(&svms->draining_faults, 1);
 	for_each_set_bit(i, svms->bitmap_supported, p->n_pdds) {
 		pdd = p->pdds[i];
 		if (!pdd)
@@ -1975,6 +1976,7 @@ void svm_range_drain_retry_fault(struct svm_range_list *svms)
 		flush_work(&adev->irq.ih1_work);
 		pr_debug("drain retry fault gpu %d svms 0x%p done\n", i, svms);
 	}
+	atomic_set(&svms->draining_faults, 0);
 }
 
 static void svm_range_deferred_list_work(struct work_struct *work)
@@ -2002,6 +2004,7 @@ static void svm_range_deferred_list_work(struct work_struct *work)
 	 * mmap write lock to serialize with munmap notifiers.
 	 */
 	if (unlikely(READ_ONCE(svms->drain_pagefaults))) {
+		atomic_set(&svms->draining_faults, 1);
 		WRITE_ONCE(svms->drain_pagefaults, false);
 		mmap_write_unlock(mm);
 		svm_range_drain_retry_fault(svms);
@@ -2049,12 +2052,6 @@ 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);
@@ -2133,6 +2130,13 @@ 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".
+	 */
+	pr_debug("set range drain_pagefaults true\n");
+	WRITE_ONCE(svms->drain_pagefaults, true);
+
 	unmap_parent = start <= prange->start && last >= prange->last;
 
 	list_for_each_entry(pchild, &prange->child_list, child_list) {
@@ -2595,6 +2599,13 @@ svm_range_restore_pages(struct amdgpu_device *adev, unsigned int pasid,
 	mm = p->mm;
 	mmap_write_lock(mm);
 
+	if (!!atomic_read(&svms->draining_faults) ||
+	    READ_ONCE(svms->drain_pagefaults)) {
+		pr_debug("draining retry fault, drop fault 0x%llx\n", addr);
+		mmap_write_downgrade(mm);
+		goto out_unlock_mm;
+	}
+
 	vma = find_vma(p->mm, addr << PAGE_SHIFT);
 	if (!vma || (addr << PAGE_SHIFT) < vma->vm_start) {
 		pr_debug("VMA not found for address 0x%llx\n", addr);
@@ -2732,6 +2743,7 @@ 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->draining_faults, 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);
-- 
2.17.1