Re: [PATCH] drm/i915/ttm: fix sg_table construction

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On 7/8/2022 9:41 AM, Matthew Auld wrote:
If we encounter some monster sized local-memory page that exceeds the
maximum sg length (UINT32_MAX), ensure that don't end up with some
misaligned address in the entry that follows, leading to fireworks
later. Also ensure we have some coverage of this in the selftests.

v2(Chris): use round_down consistently to avoid udiv errors

Fixes: f701b16d4cc5 ("drm/i915/ttm: add i915_sg_from_buddy_resource")
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/6379
Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Cc: Nirmoy Das <nirmoy.das@xxxxxxxxxxxxxxx>
---
  drivers/gpu/drm/i915/gem/i915_gem_ttm.c       | 11 +++++++++--
  drivers/gpu/drm/i915/i915_scatterlist.c       | 19 +++++++++++++++----
  drivers/gpu/drm/i915/i915_scatterlist.h       |  6 ++++--
  drivers/gpu/drm/i915/intel_region_ttm.c       | 10 +++++++---
  drivers/gpu/drm/i915/intel_region_ttm.h       |  3 ++-
  .../drm/i915/selftests/intel_memory_region.c  | 17 ++++++++++++++++-
  drivers/gpu/drm/i915/selftests/mock_region.c  |  3 ++-
  7 files changed, 55 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
index 7e1f8b83077f..c5c8aa1f8558 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
@@ -602,10 +602,15 @@ i915_ttm_resource_get_st(struct drm_i915_gem_object *obj,
  			 struct ttm_resource *res)
  {
  	struct ttm_buffer_object *bo = i915_gem_to_ttm(obj);
+	u64 page_alignment;
if (!i915_ttm_gtt_binds_lmem(res))
  		return i915_ttm_tt_get_st(bo->ttm);
+ page_alignment = bo->page_alignment << PAGE_SHIFT;
+	if (!page_alignment)
+		page_alignment = obj->mm.region->min_page_size;
+
  	/*
  	 * If CPU mapping differs, we need to add the ttm_tt pages to
  	 * the resulting st. Might make sense for GGTT.
@@ -616,7 +621,8 @@ i915_ttm_resource_get_st(struct drm_i915_gem_object *obj,
  			struct i915_refct_sgt *rsgt;
rsgt = intel_region_ttm_resource_to_rsgt(obj->mm.region,
-								 res);
+								 res,
+								 page_alignment);
  			if (IS_ERR(rsgt))
  				return rsgt;
@@ -625,7 +631,8 @@ i915_ttm_resource_get_st(struct drm_i915_gem_object *obj,
  		return i915_refct_sgt_get(obj->ttm.cached_io_rsgt);
  	}
- return intel_region_ttm_resource_to_rsgt(obj->mm.region, res);
+	return intel_region_ttm_resource_to_rsgt(obj->mm.region, res,
+						 page_alignment);
  }
static int i915_ttm_truncate(struct drm_i915_gem_object *obj)
diff --git a/drivers/gpu/drm/i915/i915_scatterlist.c b/drivers/gpu/drm/i915/i915_scatterlist.c
index 159571b9bd24..f63b50b71e10 100644
--- a/drivers/gpu/drm/i915/i915_scatterlist.c
+++ b/drivers/gpu/drm/i915/i915_scatterlist.c
@@ -68,6 +68,7 @@ void i915_refct_sgt_init(struct i915_refct_sgt *rsgt, size_t size)
   * drm_mm_node
   * @node: The drm_mm_node.
   * @region_start: An offset to add to the dma addresses of the sg list.
+ * @page_alignment: Required page alignment for each sg entry. Power of two.
   *
   * Create a struct sg_table, initializing it from a struct drm_mm_node,
   * taking a maximum segment length into account, splitting into segments
@@ -77,15 +78,18 @@ void i915_refct_sgt_init(struct i915_refct_sgt *rsgt, size_t size)
   * error code cast to an error pointer on failure.
   */
  struct i915_refct_sgt *i915_rsgt_from_mm_node(const struct drm_mm_node *node,
-					      u64 region_start)
+					      u64 region_start,
+					      u64 page_alignment)
  {
-	const u64 max_segment = SZ_1G; /* Do we have a limit on this? */
+	const u64 max_segment = round_down(UINT_MAX, page_alignment);
  	u64 segment_pages = max_segment >> PAGE_SHIFT;
  	u64 block_size, offset, prev_end;
  	struct i915_refct_sgt *rsgt;
  	struct sg_table *st;
  	struct scatterlist *sg;
+ GEM_BUG_ON(!max_segment);
+
  	rsgt = kmalloc(sizeof(*rsgt), GFP_KERNEL);
  	if (!rsgt)
  		return ERR_PTR(-ENOMEM);
@@ -112,6 +116,8 @@ struct i915_refct_sgt *i915_rsgt_from_mm_node(const struct drm_mm_node *node,
  				sg = __sg_next(sg);
sg_dma_address(sg) = region_start + offset;
+			GEM_BUG_ON(!IS_ALIGNED(sg_dma_address(sg),
+					       page_alignment));
  			sg_dma_len(sg) = 0;
  			sg->length = 0;
  			st->nents++;
@@ -138,6 +144,7 @@ struct i915_refct_sgt *i915_rsgt_from_mm_node(const struct drm_mm_node *node,
   * i915_buddy_block list
   * @res: The struct i915_ttm_buddy_resource.
   * @region_start: An offset to add to the dma addresses of the sg list.
+ * @page_alignment: Required page alignment for each sg entry. Power of two.
   *
   * Create a struct sg_table, initializing it from struct i915_buddy_block list,
   * taking a maximum segment length into account, splitting into segments
@@ -147,11 +154,12 @@ struct i915_refct_sgt *i915_rsgt_from_mm_node(const struct drm_mm_node *node,
   * error code cast to an error pointer on failure.
   */
  struct i915_refct_sgt *i915_rsgt_from_buddy_resource(struct ttm_resource *res,
-						     u64 region_start)
+						     u64 region_start,
+						     u64 page_alignment)
  {
  	struct i915_ttm_buddy_resource *bman_res = to_ttm_buddy_resource(res);
  	const u64 size = res->num_pages << PAGE_SHIFT;
-	const u64 max_segment = rounddown(UINT_MAX, PAGE_SIZE);
+	const u64 max_segment = round_down(UINT_MAX, page_alignment);
  	struct drm_buddy *mm = bman_res->mm;
  	struct list_head *blocks = &bman_res->blocks;
  	struct drm_buddy_block *block;
@@ -161,6 +169,7 @@ struct i915_refct_sgt *i915_rsgt_from_buddy_resource(struct ttm_resource *res,
  	resource_size_t prev_end;
GEM_BUG_ON(list_empty(blocks));
+	GEM_BUG_ON(!max_segment);
rsgt = kmalloc(sizeof(*rsgt), GFP_KERNEL);
  	if (!rsgt)
@@ -191,6 +200,8 @@ struct i915_refct_sgt *i915_rsgt_from_buddy_resource(struct ttm_resource *res,
  					sg = __sg_next(sg);
sg_dma_address(sg) = region_start + offset;
+				GEM_BUG_ON(!IS_ALIGNED(sg_dma_address(sg),
+						       page_alignment));
  				sg_dma_len(sg) = 0;
  				sg->length = 0;
  				st->nents++;
diff --git a/drivers/gpu/drm/i915/i915_scatterlist.h b/drivers/gpu/drm/i915/i915_scatterlist.h
index 12c6a1684081..b13e4cdea923 100644
--- a/drivers/gpu/drm/i915/i915_scatterlist.h
+++ b/drivers/gpu/drm/i915/i915_scatterlist.h
@@ -213,9 +213,11 @@ static inline void __i915_refct_sgt_init(struct i915_refct_sgt *rsgt,
  void i915_refct_sgt_init(struct i915_refct_sgt *rsgt, size_t size);
struct i915_refct_sgt *i915_rsgt_from_mm_node(const struct drm_mm_node *node,
-					      u64 region_start);
+					      u64 region_start,
+					      u64 page_alignment);
struct i915_refct_sgt *i915_rsgt_from_buddy_resource(struct ttm_resource *res,
-						     u64 region_start);
+						     u64 region_start,
+						     u64 page_alignment);
#endif
diff --git a/drivers/gpu/drm/i915/intel_region_ttm.c b/drivers/gpu/drm/i915/intel_region_ttm.c
index 62ff77445b01..6873808a7015 100644
--- a/drivers/gpu/drm/i915/intel_region_ttm.c
+++ b/drivers/gpu/drm/i915/intel_region_ttm.c
@@ -152,6 +152,7 @@ int intel_region_ttm_fini(struct intel_memory_region *mem)
   * Convert an opaque TTM resource manager resource to a refcounted sg_table.
   * @mem: The memory region.
   * @res: The resource manager resource obtained from the TTM resource manager.
+ * @page_alignment: Required page alignment for each sg entry. Power of two.
   *
   * The gem backends typically use sg-tables for operations on the underlying
   * io_memory. So provide a way for the backends to translate the
@@ -161,16 +162,19 @@ int intel_region_ttm_fini(struct intel_memory_region *mem)
   */
  struct i915_refct_sgt *
  intel_region_ttm_resource_to_rsgt(struct intel_memory_region *mem,
-				  struct ttm_resource *res)
+				  struct ttm_resource *res,
+				  u64 page_alignment)
  {
  	if (mem->is_range_manager) {
  		struct ttm_range_mgr_node *range_node =
  			to_ttm_range_mgr_node(res);
return i915_rsgt_from_mm_node(&range_node->mm_nodes[0],
-					      mem->region.start);
+					      mem->region.start,
+					      page_alignment);
  	} else {
-		return i915_rsgt_from_buddy_resource(res, mem->region.start);
+		return i915_rsgt_from_buddy_resource(res, mem->region.start,
+						     page_alignment);
  	}
  }
diff --git a/drivers/gpu/drm/i915/intel_region_ttm.h b/drivers/gpu/drm/i915/intel_region_ttm.h
index cf9d86dcf409..98fba5155619 100644
--- a/drivers/gpu/drm/i915/intel_region_ttm.h
+++ b/drivers/gpu/drm/i915/intel_region_ttm.h
@@ -24,7 +24,8 @@ int intel_region_ttm_fini(struct intel_memory_region *mem);
struct i915_refct_sgt *
  intel_region_ttm_resource_to_rsgt(struct intel_memory_region *mem,
-				  struct ttm_resource *res);
+				  struct ttm_resource *res,
+				  u64 page_alignment);
void intel_region_ttm_resource_free(struct intel_memory_region *mem,
  				    struct ttm_resource *res);
diff --git a/drivers/gpu/drm/i915/selftests/intel_memory_region.c b/drivers/gpu/drm/i915/selftests/intel_memory_region.c
index 73eb53edb8de..4e0069a87f15 100644
--- a/drivers/gpu/drm/i915/selftests/intel_memory_region.c
+++ b/drivers/gpu/drm/i915/selftests/intel_memory_region.c
@@ -460,7 +460,9 @@ static int igt_mock_max_segment(void *arg)
  	struct drm_buddy *mm;
  	struct list_head *blocks;
  	struct scatterlist *sg;
+	I915_RND_STATE(prng);
  	LIST_HEAD(objects);
+	unsigned int ps;
  	u64 size;
  	int err = 0;
@@ -472,7 +474,11 @@ static int igt_mock_max_segment(void *arg)
  	 */
size = SZ_8G;
-	mem = mock_region_create(i915, 0, size, PAGE_SIZE, 0, 0);
+	ps = PAGE_SIZE;
+	if (i915_prandom_u64_state(&prng) & 1)
+		ps = SZ_64K; /* For something like DG2 */

Hi Matt,


shouldn't max_segment also need to be adjusted accordingly here?


Nirmoy

+
+	mem = mock_region_create(i915, 0, size, ps, 0, 0);
  	if (IS_ERR(mem))
  		return PTR_ERR(mem);
@@ -498,12 +504,21 @@ static int igt_mock_max_segment(void *arg)
  	}
for (sg = obj->mm.pages->sgl; sg; sg = sg_next(sg)) {
+		dma_addr_t daddr = sg_dma_address(sg);
+
  		if (sg->length > max_segment) {
  			pr_err("%s: Created an oversized scatterlist entry, %u > %u\n",
  			       __func__, sg->length, max_segment);
  			err = -EINVAL;
  			goto out_close;
  		}
+
+		if (!IS_ALIGNED(daddr, ps)) {
+			pr_err("%s: Created an unaligned scatterlist entry, addr=%pa, ps=%u\n",
+			       __func__,  &daddr, ps);
+			err = -EINVAL;
+			goto out_close;
+		}
  	}
out_close:
diff --git a/drivers/gpu/drm/i915/selftests/mock_region.c b/drivers/gpu/drm/i915/selftests/mock_region.c
index 670557ce1024..bac21fe84ca5 100644
--- a/drivers/gpu/drm/i915/selftests/mock_region.c
+++ b/drivers/gpu/drm/i915/selftests/mock_region.c
@@ -33,7 +33,8 @@ static int mock_region_get_pages(struct drm_i915_gem_object *obj)
  		return PTR_ERR(obj->mm.res);
obj->mm.rsgt = intel_region_ttm_resource_to_rsgt(obj->mm.region,
-							 obj->mm.res);
+							 obj->mm.res,
+							 obj->mm.region->min_page_size);
  	if (IS_ERR(obj->mm.rsgt)) {
  		err = PTR_ERR(obj->mm.rsgt);
  		goto err_free_resource;



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