drm/i915: Track page table reload need

This patch was formerly known as, "Force pd restore when PDEs change,
gen6-7." I had to change the name because it is needed for GEN8 too.

The real issue this is trying to solve is when a new object is mapped
into the current address space. The GPU does not snoop the new mapping
so we must do the gen specific action to reload the page tables.

GEN8 and GEN7 do differ in the way they load page tables for the RCS.
GEN8 does so with the context restore, while GEN7 requires the proper
load commands in the command streamer. Non-render is similar for both.

Caveat for GEN7
The docs say you cannot change the PDEs of a currently running context.
We never map new PDEs of a running context, and expect them to be
present - so I think this is okay. (We can unmap, but this should also
be okay since we only unmap unreferenced objects that the GPU shouldn't
be tryingto va->pa xlate.) The MI_SET_CONTEXT command does have a flag
to signal that even if the context is the same, force a reload. It's
unclear exactly what this does, but I have a hunch it's the right thing
to do.

The logic assumes that we always emit a context switch after mapping new
PDEs, and before we submit a batch. This is the case today, and has been
the case since the inception of hardware contexts. A note in the comment
let's the user know.

It's not just for gen8. If the current context has mappings change, we
need a context reload to switch

v2: Rebased after ppgtt clean up patches. Split the warning for aliasing
and true ppgtt options. And do not break aliasing ppgtt, where to->ppgtt
is always null.

v3: Invalidate PPGTT TLBs inside alloc_va_range.

v4: Rename ppgtt_invalidate_tlbs to mark_tlbs_dirty and move
pd_dirty_rings from i915_address_space to i915_hw_ppgtt. Fixes when
neither ctx->ppgtt and aliasing_ppgtt exist.

v5: Removed references to teardown_va_range.

v6: Updated needs_pd_load_pre/post.

v7: Fix pd_dirty_rings check in needs_pd_load_post, and update/move
comment about updated PDEs to object_pin/bind (Mika).

Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Michel Thierry <michel.thierry@intel.com> (v2+)
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -4143,6 +4143,10 @@ i915_gem_object_do_pin(struct drm_i915_gem_object *obj,
 
 	bound = vma ? vma->bound : 0;
 	if (vma == NULL || !drm_mm_node_allocated(&vma->node)) {
+		/* In true PPGTT, bind has possibly changed PDEs, which
+		 * means we must do a context switch before the GPU can
+		 * accurately read some of the VMAs.
+		 */
 		vma = i915_gem_object_bind_to_vm(obj, vm, ggtt_view, alignment,
 						 flags);
 		if (IS_ERR(vma))

drivers/gpu/drm/i915/i915_gem_context.c

@@ -573,8 +573,20 @@ static inline bool should_skip_switch(struct intel_engine_cs *ring,
 				      struct intel_context *from,
 				      struct intel_context *to)
 {
-	if (from == to && !to->remap_slice)
-		return true;
+	struct drm_i915_private *dev_priv = ring->dev->dev_private;
+
+	if (to->remap_slice)
+		return false;
+
+	if (to->ppgtt) {
+		if (from == to && !test_bit(ring->id,
+				&to->ppgtt->pd_dirty_rings))
+			return true;
+	} else if (dev_priv->mm.aliasing_ppgtt) {
+		if (from == to && !test_bit(ring->id,
+				&dev_priv->mm.aliasing_ppgtt->pd_dirty_rings))
+			return true;
+	}
 
 	return false;
 }
@@ -610,10 +622,7 @@ needs_pd_load_post(struct intel_engine_cs *ring, struct intel_context *to)
 	if (ring != &dev_priv->ring[RCS])
 		return false;
 
-	if (!to->legacy_hw_ctx.initialized)
-		return true;
-
-	if (i915_gem_context_is_default(to))
+	if (to->ppgtt->pd_dirty_rings)
 		return true;
 
 	return false;
@@ -664,6 +673,9 @@ static int do_switch(struct intel_engine_cs *ring,
 		ret = to->ppgtt->switch_mm(to->ppgtt, ring);
 		if (ret)
 			goto unpin_out;
+
+		/* Doing a PD load always reloads the page dirs */
+		clear_bit(ring->id, &to->ppgtt->pd_dirty_rings);
 	}
 
 	if (ring != &dev_priv->ring[RCS]) {
@@ -696,6 +708,8 @@ static int do_switch(struct intel_engine_cs *ring,
 
 	if (!to->legacy_hw_ctx.initialized || i915_gem_context_is_default(to))
 		hw_flags |= MI_RESTORE_INHIBIT;
+	else if (to->ppgtt && test_and_clear_bit(ring->id, &to->ppgtt->pd_dirty_rings))
+		hw_flags |= MI_FORCE_RESTORE;
 
 	ret = mi_set_context(ring, to, hw_flags);
 	if (ret)

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -1251,6 +1251,13 @@ i915_gem_ringbuffer_submission(struct drm_device *dev, struct drm_file *file,
 	if (ret)
 		goto error;
 
+	if (ctx->ppgtt)
+		WARN(ctx->ppgtt->pd_dirty_rings & (1<<ring->id),
+			"%s didn't clear reload\n", ring->name);
+	else if (dev_priv->mm.aliasing_ppgtt)
+		WARN(dev_priv->mm.aliasing_ppgtt->pd_dirty_rings &
+			(1<<ring->id), "%s didn't clear reload\n", ring->name);
+
 	instp_mode = args->flags & I915_EXEC_CONSTANTS_MASK;
 	instp_mask = I915_EXEC_CONSTANTS_MASK;
 	switch (instp_mode) {

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -1162,6 +1162,16 @@ static void gen6_ppgtt_unmap_pages(struct i915_hw_ppgtt *ppgtt)
 			       4096, PCI_DMA_BIDIRECTIONAL);
 }
 
+/* PDE TLBs are a pain invalidate pre GEN8. It requires a context reload. If we
+ * are switching between contexts with the same LRCA, we also must do a force
+ * restore.
+ */
+static inline void mark_tlbs_dirty(struct i915_hw_ppgtt *ppgtt)
+{
+	/* If current vm != vm, */
+	ppgtt->pd_dirty_rings = INTEL_INFO(ppgtt->base.dev)->ring_mask;
+}
+
 static int gen6_alloc_va_range(struct i915_address_space *vm,
 			       uint64_t start, uint64_t length)
 {
@@ -1181,6 +1191,7 @@ static int gen6_alloc_va_range(struct i915_address_space *vm,
 				GEN6_PTES);
 	}
 
+	mark_tlbs_dirty(ppgtt);
 	return 0;
 }
 

drivers/gpu/drm/i915/i915_gem_gtt.h

@@ -300,6 +300,7 @@ struct i915_hw_ppgtt {
 	struct i915_address_space base;
 	struct kref ref;
 	struct drm_mm_node node;
+	unsigned long pd_dirty_rings;
 	unsigned num_pd_entries;
 	unsigned num_pd_pages; /* gen8+ */
 	union {