drm/xe: Rework GPU page fault handling

Add helper function to implement VMA (user binding) page faults, remove
unnecessary userptr.invalidate_link list del operation, retry on memory
pressure, remove unnecessary xe_vma_userptr_check_repin after rebinding,
remove unnecessary TLB invalidation, and always use vm->lock in write
mode. Changes help facilitate SVM page faults.
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Jagmeet Randhawa <jagmeet.randhawa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240607015212.2190106-1-matthew.brost@intel.com

drivers/gpu/drm/xe/xe_gt_pagefault.c

@@ -125,126 +125,108 @@ static int xe_pf_begin(struct drm_exec *exec, struct xe_vma *vma,
 	return 0;
 }
 
-static int handle_pagefault(struct xe_gt *gt, struct pagefault *pf)
+static int handle_vma_pagefault(struct xe_tile *tile, struct pagefault *pf,
+				struct xe_vma *vma)
 {
-	struct xe_device *xe = gt_to_xe(gt);
-	struct xe_tile *tile = gt_to_tile(gt);
+	struct xe_vm *vm = xe_vma_vm(vma);
 	struct drm_exec exec;
-	struct xe_vm *vm;
-	struct xe_vma *vma = NULL;
 	struct dma_fence *fence;
-	bool write_locked;
-	int ret = 0;
+	ktime_t end = 0;
+	int err;
 	bool atomic;
 
-	/* SW isn't expected to handle TRTT faults */
-	if (pf->trva_fault)
-		return -EFAULT;
-
-	/* ASID to VM */
-	mutex_lock(&xe->usm.lock);
-	vm = xa_load(&xe->usm.asid_to_vm, pf->asid);
-	if (vm && xe_vm_in_fault_mode(vm))
-		xe_vm_get(vm);
-	else
-		vm = NULL;
-	mutex_unlock(&xe->usm.lock);
-	if (!vm)
-		return -EINVAL;
-
-retry_userptr:
-	/*
-	 * TODO: Avoid exclusive lock if VM doesn't have userptrs, or
-	 * start out read-locked?
-	 */
-	down_write(&vm->lock);
-	write_locked = true;
-	vma = lookup_vma(vm, pf->page_addr);
-	if (!vma) {
-		ret = -EINVAL;
-		goto unlock_vm;
-	}
-
-	if (!xe_vma_is_userptr(vma) ||
-	    !xe_vma_userptr_check_repin(to_userptr_vma(vma))) {
-		downgrade_write(&vm->lock);
-		write_locked = false;
-	}
-
 	trace_xe_vma_pagefault(vma);
-
 	atomic = access_is_atomic(pf->access_type);
 
 	/* Check if VMA is valid */
 	if (vma_is_valid(tile, vma) && !atomic)
-		goto unlock_vm;
-
-	/* TODO: Validate fault */
+		return 0;
 
-	if (xe_vma_is_userptr(vma) && write_locked) {
+retry_userptr:
+	if (xe_vma_is_userptr(vma) &&
+	    xe_vma_userptr_check_repin(to_userptr_vma(vma))) {
 		struct xe_userptr_vma *uvma = to_userptr_vma(vma);
 
-		spin_lock(&vm->userptr.invalidated_lock);
-		list_del_init(&uvma->userptr.invalidate_link);
-		spin_unlock(&vm->userptr.invalidated_lock);
-
-		ret = xe_vma_userptr_pin_pages(uvma);
-		if (ret)
-			goto unlock_vm;
-
-		downgrade_write(&vm->lock);
-		write_locked = false;
+		err = xe_vma_userptr_pin_pages(uvma);
+		if (err)
+			return err;
 	}
 
 	/* Lock VM and BOs dma-resv */
 	drm_exec_init(&exec, 0, 0);
 	drm_exec_until_all_locked(&exec) {
-		ret = xe_pf_begin(&exec, vma, atomic, tile->id);
+		err = xe_pf_begin(&exec, vma, atomic, tile->id);
 		drm_exec_retry_on_contention(&exec);
-		if (ret)
+		if (xe_vm_validate_should_retry(&exec, err, &end))
+			err = -EAGAIN;
+		if (err)
 			goto unlock_dma_resv;
 
 		/* Bind VMA only to the GT that has faulted */
 		trace_xe_vma_pf_bind(vma);
 		fence = xe_vma_rebind(vm, vma, BIT(tile->id));
 		if (IS_ERR(fence)) {
-			ret = PTR_ERR(fence);
+			err = PTR_ERR(fence);
+			if (xe_vm_validate_should_retry(&exec, err, &end))
+				err = -EAGAIN;
 			goto unlock_dma_resv;
 		}
 	}
 
-	/*
-	 * XXX: Should we drop the lock before waiting? This only helps if doing
-	 * GPU binds which is currently only done if we have to wait for more
-	 * than 10ms on a move.
-	 */
 	dma_fence_wait(fence, false);
 	dma_fence_put(fence);
-
-	if (xe_vma_is_userptr(vma))
-		ret = xe_vma_userptr_check_repin(to_userptr_vma(vma));
 	vma->tile_invalidated &= ~BIT(tile->id);
 
 unlock_dma_resv:
 	drm_exec_fini(&exec);
-unlock_vm:
-	if (!ret)
-		vm->usm.last_fault_vma = vma;
-	if (write_locked)
-		up_write(&vm->lock);
-	else
-		up_read(&vm->lock);
-	if (ret == -EAGAIN)
+	if (err == -EAGAIN)
 		goto retry_userptr;
 
-	if (!ret) {
-		ret = xe_gt_tlb_invalidation_vma(gt, NULL, vma);
-		if (ret >= 0)
-			ret = 0;
+	return err;
+}
+
+static int handle_pagefault(struct xe_gt *gt, struct pagefault *pf)
+{
+	struct xe_device *xe = gt_to_xe(gt);
+	struct xe_tile *tile = gt_to_tile(gt);
+	struct xe_vm *vm;
+	struct xe_vma *vma = NULL;
+	int err;
+
+	/* SW isn't expected to handle TRTT faults */
+	if (pf->trva_fault)
+		return -EFAULT;
+
+	/* ASID to VM */
+	mutex_lock(&xe->usm.lock);
+	vm = xa_load(&xe->usm.asid_to_vm, pf->asid);
+	if (vm && xe_vm_in_fault_mode(vm))
+		xe_vm_get(vm);
+	else
+		vm = NULL;
+	mutex_unlock(&xe->usm.lock);
+	if (!vm)
+		return -EINVAL;
+
+	/*
+	 * TODO: Change to read lock? Using write lock for simplicity.
+	 */
+	down_write(&vm->lock);
+	vma = lookup_vma(vm, pf->page_addr);
+	if (!vma) {
+		err = -EINVAL;
+		goto unlock_vm;
 	}
+
+	err = handle_vma_pagefault(tile, pf, vma);
+
+unlock_vm:
+	if (!err)
+		vm->usm.last_fault_vma = vma;
+	up_write(&vm->lock);
 	xe_vm_put(vm);
 
-	return ret;
+	return err;
 }
 
 static int send_pagefault_reply(struct xe_guc *guc,