drm/i915: Pull i915_vma_pin under the vm->mutex

Replace the struct_mutex requirement for pinning the i915_vma with the
local vm->mutex instead. Note that the vm->mutex is tainted by the
shrinker (we require unbinding from inside fs-reclaim) and so we cannot
allocate while holding that mutex. Instead we have to preallocate
workers to do allocate and apply the PTE updates after we have we
reserved their slot in the drm_mm (using fences to order the PTE writes
with the GPU work and with later unbind).

In adding the asynchronous vma binding, one subtle requirement is to
avoid coupling the binding fence into the backing object->resv. That is
the asynchronous binding only applies to the vma timeline itself and not
to the pages as that is a more global timeline (the binding of one vma
does not need to be ordered with another vma, nor does the implicit GEM
fencing depend on a vma, only on writes to the backing store). Keeping
the vma binding distinct from the backing store timelines is verified by
a number of async gem_exec_fence and gem_exec_schedule tests. The way we
do this is quite simple, we keep the fence for the vma binding separate
and only wait on it as required, and never add it to the obj->resv
itself.

Another consequence in reducing the locking around the vma is the
destruction of the vma is no longer globally serialised by struct_mutex.
A natural solution would be to add a kref to i915_vma, but that requires
decoupling the reference cycles, possibly by introducing a new
i915_mm_pages object that is own by both obj->mm and vma->pages.
However, we have not taken that route due to the overshadowing lmem/ttm
discussions, and instead play a series of complicated games with
trylocks to (hopefully) ensure that only one destruction path is called!

v2: Add some commentary, and some helpers to reduce patch churn.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191004134015.13204-4-chris@chris-wilson.co.uk

1 files changed, 1 insertions, 28 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index c3ac5a5c5185..8f7365b8dffb 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -2079,7 +2079,6 @@ intel_pin_and_fence_fb_obj(struct drm_framebuffer *fb,
 	unsigned int pinctl;
 	u32 alignment;
 
-	WARN_ON(!mutex_is_locked(&dev->struct_mutex));
 	if (WARN_ON(!i915_gem_object_is_framebuffer(obj)))
 		return ERR_PTR(-EINVAL);
 
@@ -2163,8 +2162,6 @@ err:
 
 void intel_unpin_fb_vma(struct i915_vma *vma, unsigned long flags)
 {
-	lockdep_assert_held(&vma->vm->i915->drm.struct_mutex);
-
 	i915_gem_object_lock(vma->obj);
 	if (flags & PLANE_HAS_FENCE)
 		i915_vma_unpin_fence(vma);
@@ -3065,12 +3062,10 @@ intel_alloc_initial_plane_obj(struct intel_crtc *crtc,
 		return false;
 	}
 
-	mutex_lock(&dev->struct_mutex);
 	obj = i915_gem_object_create_stolen_for_preallocated(dev_priv,
 							     base_aligned,
 							     base_aligned,
 							     size_aligned);
-	mutex_unlock(&dev->struct_mutex);
 	if (!obj)
 		return false;
 
@@ -3232,13 +3227,11 @@ valid_fb:
 	intel_state->color_plane[0].stride =
 		intel_fb_pitch(fb, 0, intel_state->base.rotation);
 
-	mutex_lock(&dev->struct_mutex);
 	intel_state->vma =
 		intel_pin_and_fence_fb_obj(fb,
 					   &intel_state->view,
 					   intel_plane_uses_fence(intel_state),
 					   &intel_state->flags);
-	mutex_unlock(&dev->struct_mutex);
 	if (IS_ERR(intel_state->vma)) {
 		DRM_ERROR("failed to pin boot fb on pipe %d: %li\n",
 			  intel_crtc->pipe, PTR_ERR(intel_state->vma));
@@ -14365,8 +14358,6 @@ static void fb_obj_bump_render_priority(struct drm_i915_gem_object *obj)
  * bits.  Some older platforms need special physical address handling for
  * cursor planes.
  *
- * Must be called with struct_mutex held.
- *
  * Returns 0 on success, negative error code on failure.
  */
 int
@@ -14423,15 +14414,8 @@ intel_prepare_plane_fb(struct drm_plane *plane,
 	if (ret)
 		return ret;
 
-	ret = mutex_lock_interruptible(&dev_priv->drm.struct_mutex);
-	if (ret) {
-		i915_gem_object_unpin_pages(obj);
-		return ret;
-	}
-
 	ret = intel_plane_pin_fb(to_intel_plane_state(new_state));
 
-	mutex_unlock(&dev_priv->drm.struct_mutex);
 	i915_gem_object_unpin_pages(obj);
 	if (ret)
 		return ret;
@@ -14480,8 +14464,6 @@ intel_prepare_plane_fb(struct drm_plane *plane,
  * @old_state: the state from the previous modeset
  *
  * Cleans up a framebuffer that has just been removed from a plane.
- *
- * Must be called with struct_mutex held.
  */
 void
 intel_cleanup_plane_fb(struct drm_plane *plane,
@@ -14497,9 +14479,7 @@ intel_cleanup_plane_fb(struct drm_plane *plane,
 	}
 
 	/* Should only be called after a successful intel_prepare_plane_fb()! */
-	mutex_lock(&dev_priv->drm.struct_mutex);
 	intel_plane_unpin_fb(to_intel_plane_state(old_state));
-	mutex_unlock(&dev_priv->drm.struct_mutex);
 }
 
 int
@@ -14702,7 +14682,6 @@ intel_legacy_cursor_update(struct drm_plane *plane,
 			   u32 src_w, u32 src_h,
 			   struct drm_modeset_acquire_ctx *ctx)
 {
-	struct drm_i915_private *dev_priv = to_i915(crtc->dev);
 	struct drm_plane_state *old_plane_state, *new_plane_state;
 	struct intel_plane *intel_plane = to_intel_plane(plane);
 	struct intel_crtc_state *crtc_state =
@@ -14768,13 +14747,9 @@ intel_legacy_cursor_update(struct drm_plane *plane,
 	if (ret)
 		goto out_free;
 
-	ret = mutex_lock_interruptible(&dev_priv->drm.struct_mutex);
-	if (ret)
-		goto out_free;
-
 	ret = intel_plane_pin_fb(to_intel_plane_state(new_plane_state));
 	if (ret)
-		goto out_unlock;
+		goto out_free;
 
 	intel_frontbuffer_flush(to_intel_frontbuffer(fb), ORIGIN_FLIP);
 	intel_frontbuffer_track(to_intel_frontbuffer(old_plane_state->fb),
@@ -14804,8 +14779,6 @@ intel_legacy_cursor_update(struct drm_plane *plane,
 
 	intel_plane_unpin_fb(to_intel_plane_state(old_plane_state));
 
-out_unlock:
-	mutex_unlock(&dev_priv->drm.struct_mutex);
 out_free:
 	if (new_crtc_state)
 		intel_crtc_destroy_state(crtc, &new_crtc_state->base);