drm/i915/gtt: Read-only pages for insert_entries on bdw+

commit 250f8c81

 upstream.

Hook up the flags to allow read-only ppGTT mappings for gen8+

v2: Include a selftest to check that writes to a readonly PTE are
dropped
v3: Don't duplicate cpu_check() as we can just reuse it, and even worse
don't wholesale copy the theory-of-operation comment from igt_ctx_exec
without changing it to explain the intention behind the new test!
v4: Joonas really likes magic mystery values
Signed-off-by: Jon Bloomfield <jon.bloomfield@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Matthew Auld <matthew.william.auld@gmail.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.william.auld@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180712185315.3288-2-chris@chris-wilson.co.uk

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -152,7 +152,8 @@ static int ppgtt_bind_vma(struct i915_vma *vma,
 {
 	u32 pte_flags = 0;
 
-	/* Currently applicable only to VLV */
+	/* Applicable to VLV, and gen8+ */
+	pte_flags = 0;
 	if (vma->obj->gt_ro)
 		pte_flags |= PTE_READ_ONLY;
 
@@ -783,7 +784,8 @@ gen8_ppgtt_insert_pte_entries(struct i915_address_space *vm,
 			      struct i915_page_directory_pointer *pdp,
 			      struct sg_page_iter *sg_iter,
 			      uint64_t start,
-			      enum i915_cache_level cache_level)
+			      enum i915_cache_level cache_level,
+			      u32 flags)
 {
 	struct i915_hw_ppgtt *ppgtt =
 		container_of(vm, struct i915_hw_ppgtt, base);
@@ -803,7 +805,7 @@ gen8_ppgtt_insert_pte_entries(struct i915_address_space *vm,
 
 		pt_vaddr[pte] =
 			gen8_pte_encode(sg_page_iter_dma_address(sg_iter),
-					cache_level, true, 0);
+					cache_level, true, flags);
 		if (++pte == GEN8_PTES) {
 			kunmap_px(ppgtt, pt_vaddr);
 			pt_vaddr = NULL;
@@ -824,7 +826,7 @@ static void gen8_ppgtt_insert_entries(struct i915_address_space *vm,
 				      struct sg_table *pages,
 				      uint64_t start,
 				      enum i915_cache_level cache_level,
-				      u32 unused)
+				      u32 flags)
 {
 	struct i915_hw_ppgtt *ppgtt =
 		container_of(vm, struct i915_hw_ppgtt, base);
@@ -834,7 +836,7 @@ static void gen8_ppgtt_insert_entries(struct i915_address_space *vm,
 
 	if (!USES_FULL_48BIT_PPGTT(vm->dev)) {
 		gen8_ppgtt_insert_pte_entries(vm, &ppgtt->pdp, &sg_iter, start,
-					      cache_level);
+					      cache_level, flags);
 	} else {
 		struct i915_page_directory_pointer *pdp;
 		uint64_t templ4, pml4e;
@@ -842,7 +844,7 @@ static void gen8_ppgtt_insert_entries(struct i915_address_space *vm,
 
 		gen8_for_each_pml4e(pdp, &ppgtt->pml4, start, length, templ4, pml4e) {
 			gen8_ppgtt_insert_pte_entries(vm, pdp, &sg_iter,
-						      start, cache_level);
+						      start, cache_level, flags);
 		}
 	}
 }
@@ -1519,6 +1521,10 @@ static int gen8_ppgtt_init(struct i915_hw_ppgtt *ppgtt)
 	ppgtt->base.clear_range = gen8_ppgtt_clear_range;
 	ppgtt->base.unbind_vma = ppgtt_unbind_vma;
 	ppgtt->base.bind_vma = ppgtt_bind_vma;
+
+	/* From bdw, there is support for read-only pages in the PPGTT */
+	ppgtt->base.has_read_only = true;
+
 	ppgtt->debug_dump = gen8_dump_ppgtt;
 
 	if (USES_FULL_48BIT_PPGTT(ppgtt->base.dev)) {
@@ -2347,7 +2353,7 @@ static void gen8_set_pte(void __iomem *addr, gen8_pte_t pte)
 static void gen8_ggtt_insert_entries(struct i915_address_space *vm,
 				     struct sg_table *st,
 				     uint64_t start,
-				     enum i915_cache_level level, u32 unused)
+				     enum i915_cache_level level, u32 flags)
 {
 	struct drm_i915_private *dev_priv = vm->dev->dev_private;
 	unsigned first_entry = start >> PAGE_SHIFT;
@@ -2361,7 +2367,7 @@ static void gen8_ggtt_insert_entries(struct i915_address_space *vm,
 		addr = sg_dma_address(sg_iter.sg) +
 			(sg_iter.sg_pgoffset << PAGE_SHIFT);
 		gen8_set_pte(&gtt_entries[i],
-			     gen8_pte_encode(addr, level, true, 0));
+			     gen8_pte_encode(addr, level, true, flags));
 		i++;
 	}
 
@@ -2374,7 +2380,7 @@ static void gen8_ggtt_insert_entries(struct i915_address_space *vm,
 	 */
 	if (i != 0)
 		WARN_ON(readq(&gtt_entries[i-1])
-			!= gen8_pte_encode(addr, level, true, 0));
+			!= gen8_pte_encode(addr, level, true, flags));
 
 	/* This next bit makes the above posting read even more important. We
 	 * want to flush the TLBs only after we're certain all the PTE updates
@@ -2514,7 +2520,8 @@ static int ggtt_bind_vma(struct i915_vma *vma,
 	if (ret)
 		return ret;
 
-	/* Currently applicable only to VLV */
+	/* Applicable to VLV (gen8+ do not support RO in the GGTT) */
+	pte_flags = 0;
 	if (obj->gt_ro)
 		pte_flags |= PTE_READ_ONLY;
 
@@ -2657,6 +2664,9 @@ static int i915_gem_setup_global_gtt(struct drm_device *dev,
 	i915_address_space_init(ggtt_vm, dev_priv);
 	ggtt_vm->total += PAGE_SIZE;
 
+	/* Only VLV supports read-only GGTT mappings */
+	ggtt_vm->has_read_only = IS_VALLEYVIEW(dev_priv);
+
 	if (intel_vgpu_active(dev)) {
 		ret = intel_vgt_balloon(dev);
 		if (ret)

drivers/gpu/drm/i915/i915_gem_gtt.h

@@ -307,6 +307,9 @@ struct i915_address_space {
 	 */
 	struct list_head inactive_list;
 
+	/* Some systems support read-only mappings for GGTT and/or PPGTT */
+	bool has_read_only:1;
+
 	/* FIXME: Need a more generic return type */
 	gen6_pte_t (*pte_encode)(dma_addr_t addr,
 				 enum i915_cache_level level,

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -2058,6 +2058,8 @@ static void intel_destroy_ringbuffer_obj(struct intel_ringbuffer *ringbuf)
 static int intel_alloc_ringbuffer_obj(struct drm_device *dev,
 				      struct intel_ringbuffer *ringbuf)
 {
+	struct drm_i915_private *dev_priv = to_i915(dev);
+	struct i915_address_space *vm = &dev_priv->gtt.base;
 	struct drm_i915_gem_object *obj;
 
 	obj = NULL;
@@ -2068,8 +2070,12 @@ static int intel_alloc_ringbuffer_obj(struct drm_device *dev,
 	if (obj == NULL)
 		return -ENOMEM;
 
-	/* mark ring buffers as read-only from GPU side by default */
-	obj->gt_ro = 1;
+	/*
+	 * Mark ring buffers as read-only from GPU side (so no stray overwrites)
+	 * if supported by the platform's GGTT.
+	 */
+	if (vm->has_read_only)
+		obj->gt_ro = 1;
 
 	ringbuf->obj = obj;