drm/i915: Add support for moving fence waiting

For now, we will only allow async migration when TTM is used,
so the paths we care about are related to TTM.

The mmap path is handled by having the fence in ttm_bo->moving,
when pinning, the binding only becomes available after the moving
fence is signaled, and pinning a cpu map will only work after
the moving fence signals.

This should close all holes where userspace can read a buffer
before it's fully migrated.

v2:
- Fix a couple of SPARSE warnings
v3:
- Fix a NULL pointer dereference
v4:
- Ditch the moving fence waiting for i915_vma_pin_iomap() and
  replace with a verification that the vma is already bound.
  (Matthew Auld)
- Squash with a previous patch introducing moving fence waiting and
  accessing interfaces (Matthew Auld)
- Rename to indicated that we also add support for sync waiting.

Co-developed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

drivers/gpu/drm/i915/gem/i915_gem_object.c

@@ -33,6 +33,7 @@
 #include "i915_gem_object.h"
 #include "i915_memcpy.h"
 #include "i915_trace.h"
+#include "i915_gem_ttm.h"
 
 static struct kmem_cache *slab_objects;
 
@@ -726,6 +727,57 @@ static const struct drm_gem_object_funcs i915_gem_object_funcs = {
 	.export = i915_gem_prime_export,
 };
 
+/**
+ * i915_gem_object_get_moving_fence - Get the object's moving fence if any
+ * @obj: The object whose moving fence to get.
+ *
+ * A non-signaled moving fence means that there is an async operation
+ * pending on the object that needs to be waited on before setting up
+ * any GPU- or CPU PTEs to the object's pages.
+ *
+ * Return: A refcounted pointer to the object's moving fence if any,
+ * NULL otherwise.
+ */
+struct dma_fence *
+i915_gem_object_get_moving_fence(struct drm_i915_gem_object *obj)
+{
+	return dma_fence_get(i915_gem_to_ttm(obj)->moving);
+}
+
+/**
+ * i915_gem_object_wait_moving_fence - Wait for the object's moving fence if any
+ * @obj: The object whose moving fence to wait for.
+ * @intr: Whether to wait interruptible.
+ *
+ * If the moving fence signaled without an error, it is detached from the
+ * object and put.
+ *
+ * Return: 0 if successful, -ERESTARTSYS if the wait was interrupted,
+ * negative error code if the async operation represented by the
+ * moving fence failed.
+ */
+int i915_gem_object_wait_moving_fence(struct drm_i915_gem_object *obj,
+				      bool intr)
+{
+	struct dma_fence *fence = i915_gem_to_ttm(obj)->moving;
+	int ret;
+
+	assert_object_held(obj);
+	if (!fence)
+		return 0;
+
+	ret = dma_fence_wait(fence, intr);
+	if (ret)
+		return ret;
+
+	if (fence->error)
+		return fence->error;
+
+	i915_gem_to_ttm(obj)->moving = NULL;
+	dma_fence_put(fence);
+	return 0;
+}
+
 #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
 #include "selftests/huge_gem_object.c"
 #include "selftests/huge_pages.c"

drivers/gpu/drm/i915/gem/i915_gem_object.h

@@ -517,6 +517,12 @@ i915_gem_object_finish_access(struct drm_i915_gem_object *obj)
 	i915_gem_object_unpin_pages(obj);
 }
 
+struct dma_fence *
+i915_gem_object_get_moving_fence(struct drm_i915_gem_object *obj);
+
+int i915_gem_object_wait_moving_fence(struct drm_i915_gem_object *obj,
+				      bool intr);
+
 void i915_gem_object_set_cache_coherency(struct drm_i915_gem_object *obj,
 					 unsigned int cache_level);
 bool i915_gem_object_can_bypass_llc(struct drm_i915_gem_object *obj);

drivers/gpu/drm/i915/gem/i915_gem_pages.c

@@ -418,6 +418,12 @@ void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj,
 	}
 
 	if (!ptr) {
+		err = i915_gem_object_wait_moving_fence(obj, true);
+		if (err) {
+			ptr = ERR_PTR(err);
+			goto err_unpin;
+		}
+
 		if (GEM_WARN_ON(type == I915_MAP_WC &&
 				!static_cpu_has(X86_FEATURE_PAT)))
 			ptr = ERR_PTR(-ENODEV);

drivers/gpu/drm/i915/i915_vma.c

@@ -354,6 +354,25 @@ int i915_vma_wait_for_bind(struct i915_vma *vma)
 	return err;
 }
 
+#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
+static int i915_vma_verify_bind_complete(struct i915_vma *vma)
+{
+	int err = 0;
+
+	if (i915_active_has_exclusive(&vma->active)) {
+		struct dma_fence *fence =
+			i915_active_fence_get(&vma->active.excl);
+
+		if (dma_fence_is_signaled(fence))
+			err = fence->error;
+		else
+			err = -EBUSY;
+	}
+
+	return err;
+}
+#endif
+
 /**
  * i915_vma_bind - Sets up PTEs for an VMA in it's corresponding address space.
  * @vma: VMA to map
@@ -428,6 +447,13 @@ int i915_vma_bind(struct i915_vma *vma,
 			work->pinned = i915_gem_object_get(vma->obj);
 		}
 	} else {
+		if (vma->obj) {
+			int ret;
+
+			ret = i915_gem_object_wait_moving_fence(vma->obj, true);
+			if (ret)
+				return ret;
+		}
 		vma->ops->bind_vma(vma->vm, NULL, vma, cache_level, bind_flags);
 	}
 
@@ -449,6 +475,7 @@ void __iomem *i915_vma_pin_iomap(struct i915_vma *vma)
 
 	GEM_BUG_ON(!i915_vma_is_ggtt(vma));
 	GEM_BUG_ON(!i915_vma_is_bound(vma, I915_VMA_GLOBAL_BIND));
+	GEM_BUG_ON(i915_vma_verify_bind_complete(vma));
 
 	ptr = READ_ONCE(vma->iomap);
 	if (ptr == NULL) {
@@ -867,6 +894,7 @@ int i915_vma_pin_ww(struct i915_vma *vma, struct i915_gem_ww_ctx *ww,
 		    u64 size, u64 alignment, u64 flags)
 {
 	struct i915_vma_work *work = NULL;
+	struct dma_fence *moving = NULL;
 	intel_wakeref_t wakeref = 0;
 	unsigned int bound;
 	int err;
@@ -892,7 +920,8 @@ int i915_vma_pin_ww(struct i915_vma *vma, struct i915_gem_ww_ctx *ww,
 	if (flags & PIN_GLOBAL)
 		wakeref = intel_runtime_pm_get(&vma->vm->i915->runtime_pm);
 
-	if (flags & vma->vm->bind_async_flags) {
+	moving = vma->obj ? i915_gem_object_get_moving_fence(vma->obj) : NULL;
+	if (flags & vma->vm->bind_async_flags || moving) {
 		/* lock VM */
 		err = i915_vm_lock_objects(vma->vm, ww);
 		if (err)
@@ -906,6 +935,8 @@ int i915_vma_pin_ww(struct i915_vma *vma, struct i915_gem_ww_ctx *ww,
 
 		work->vm = i915_vm_get(vma->vm);
 
+		dma_fence_work_chain(&work->base, moving);
+
 		/* Allocate enough page directories to used PTE */
 		if (vma->vm->allocate_va_range) {
 			err = i915_vm_alloc_pt_stash(vma->vm,
@@ -1010,7 +1041,10 @@ int i915_vma_pin_ww(struct i915_vma *vma, struct i915_gem_ww_ctx *ww,
 err_rpm:
 	if (wakeref)
 		intel_runtime_pm_put(&vma->vm->i915->runtime_pm, wakeref);
+	if (moving)
+		dma_fence_put(moving);
 	vma_put_pages(vma);
+
 	return err;
 }