[RFC 06/17] drm: i915: fix sg_table nents vs. orig_nents misuse

[Marek Szyprowski <m.szyprowski@samsung.com>]

The Documentation/DMA-API-HOWTO.txt states that dma_map_sg returns the
numer of the created entries in the DMA address space. However the
subsequent calls to dma_sync_sg_for_{device,cpu} and dma_unmap_sg must be
called with the original number of entries passed to dma_map_sg. The
sg_table->nents in turn holds the result of the dma_map_sg call as stated
in include/linux/scatterlist.h. Adapt the code to obey those rules.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c       | 13 +++++++------
 drivers/gpu/drm/i915/gem/i915_gem_internal.c     |  4 ++--
 drivers/gpu/drm/i915/gem/i915_gem_region.c       |  4 ++--
 drivers/gpu/drm/i915/gem/i915_gem_shmem.c        |  5 +++--
 drivers/gpu/drm/i915/gem/selftests/huge_pages.c  | 10 +++++-----
 drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c |  5 +++--
 drivers/gpu/drm/i915/gt/intel_ggtt.c             | 12 ++++++------
 drivers/gpu/drm/i915/i915_gem_gtt.c              | 12 +++++++-----
 drivers/gpu/drm/i915/i915_scatterlist.c          |  4 ++--
 drivers/gpu/drm/i915/selftests/scatterlist.c     |  8 ++++----
 10 files changed, 41 insertions(+), 36 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
index 7db5a79..d829852 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
@@ -36,21 +36,22 @@ static struct sg_table *i915_gem_map_dma_buf(struct dma_buf_attachment *attachme
 		goto err_unpin_pages;
 	}
 
-	ret = sg_alloc_table(st, obj->mm.pages->nents, GFP_KERNEL);
+	ret = sg_alloc_table(st, obj->mm.pages->orig_nents, GFP_KERNEL);
 	if (ret)
 		goto err_free;
 
 	src = obj->mm.pages->sgl;
 	dst = st->sgl;
-	for (i = 0; i < obj->mm.pages->nents; i++) {
+	for (i = 0; i < obj->mm.pages->orig_nents; i++) {
 		sg_set_page(dst, sg_page(src), src->length, 0);
 		dst = sg_next(dst);
 		src = sg_next(src);
 	}
 
-	if (!dma_map_sg_attrs(attachment->dev,
-			      st->sgl, st->nents, dir,
-			      DMA_ATTR_SKIP_CPU_SYNC)) {
+	st->nents = dma_map_sg_attrs(attachment->dev,
+				     st->sgl, st->orig_nents, dir,
+				     DMA_ATTR_SKIP_CPU_SYNC);
+	if (!st->nents) {
 		ret = -ENOMEM;
 		goto err_free_sg;
 	}
@@ -74,7 +75,7 @@ static void i915_gem_unmap_dma_buf(struct dma_buf_attachment *attachment,
 	struct drm_i915_gem_object *obj = dma_buf_to_obj(attachment->dmabuf);
 
 	dma_unmap_sg_attrs(attachment->dev,
-			   sg->sgl, sg->nents, dir,
+			   sg->sgl, sg->orig_nents, dir,
 			   DMA_ATTR_SKIP_CPU_SYNC);
 	sg_free_table(sg);
 	kfree(sg);
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_internal.c b/drivers/gpu/drm/i915/gem/i915_gem_internal.c
index cbbff81..a8ebfdd 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_internal.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_internal.c
@@ -73,7 +73,7 @@ static int i915_gem_object_get_pages_internal(struct drm_i915_gem_object *obj)
 	}
 
 	sg = st->sgl;
-	st->nents = 0;
+	st->nents = st->orig_nents = 0;
 	sg_page_sizes = 0;
 
 	do {
@@ -94,7 +94,7 @@ static int i915_gem_object_get_pages_internal(struct drm_i915_gem_object *obj)
 
 		sg_set_page(sg, page, PAGE_SIZE << order, 0);
 		sg_page_sizes |= PAGE_SIZE << order;
-		st->nents++;
+		st->nents = st->orig_nents = st->nents + 1;
 
 		npages -= 1 << order;
 		if (!npages) {
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_region.c b/drivers/gpu/drm/i915/gem/i915_gem_region.c
index 1515384..58ca560 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_region.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_region.c
@@ -53,7 +53,7 @@
 	GEM_BUG_ON(list_empty(blocks));
 
 	sg = st->sgl;
-	st->nents = 0;
+	st->nents = st->orig_nents = 0;
 	sg_page_sizes = 0;
 	prev_end = (resource_size_t)-1;
 
@@ -78,7 +78,7 @@
 
 			sg->length = block_size;
 
-			st->nents++;
+			st->nents = st->orig_nents = st->nents + 1;
 		} else {
 			sg->length += block_size;
 			sg_dma_len(sg) += block_size;
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
index 5d5d7ee..851a732 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
@@ -80,7 +80,7 @@ static int shmem_get_pages(struct drm_i915_gem_object *obj)
 	noreclaim |= __GFP_NORETRY | __GFP_NOWARN;
 
 	sg = st->sgl;
-	st->nents = 0;
+	st->nents = st->orig_nents = 0;
 	sg_page_sizes = 0;
 	for (i = 0; i < page_count; i++) {
 		const unsigned int shrink[] = {
@@ -140,7 +140,8 @@ static int shmem_get_pages(struct drm_i915_gem_object *obj)
 				sg_page_sizes |= sg->length;
 				sg = sg_next(sg);
 			}
-			st->nents++;
+			st->nents = st->orig_nents = st->nents + 1;
+
 			sg_set_page(sg, page, PAGE_SIZE, 0);
 		} else {
 			sg->length += PAGE_SIZE;
diff --git a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c
index c9988b6..bd141f9 100644
--- a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c
+++ b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c
@@ -76,7 +76,7 @@ static int get_huge_pages(struct drm_i915_gem_object *obj)
 
 	rem = obj->base.size;
 	sg = st->sgl;
-	st->nents = 0;
+	st->nents = st->orig_nents = 0;
 	sg_page_sizes = 0;
 
 	/*
@@ -99,7 +99,7 @@ static int get_huge_pages(struct drm_i915_gem_object *obj)
 
 			sg_set_page(sg, page, page_size, 0);
 			sg_page_sizes |= page_size;
-			st->nents++;
+			st->nents = st->orig_nents = st->nents + 1;
 
 			rem -= page_size;
 			if (!rem) {
@@ -201,7 +201,7 @@ static int fake_get_huge_pages(struct drm_i915_gem_object *obj)
 	/* Use optimal page sized chunks to fill in the sg table */
 	rem = obj->base.size;
 	sg = st->sgl;
-	st->nents = 0;
+	st->nents = st->orig_nents = 0;
 	sg_page_sizes = 0;
 	do {
 		unsigned int page_size = get_largest_page_size(i915, rem);
@@ -217,7 +217,7 @@ static int fake_get_huge_pages(struct drm_i915_gem_object *obj)
 
 		sg_page_sizes |= len;
 
-		st->nents++;
+		st->nents = st->orig_nents = st->nents + 1;
 
 		rem -= len;
 		if (!rem) {
@@ -252,7 +252,7 @@ static int fake_get_huge_pages_single(struct drm_i915_gem_object *obj)
 	}
 
 	sg = st->sgl;
-	st->nents = 1;
+	st->nents = st->orig_nents = 1;
 
 	page_size = get_largest_page_size(i915, obj->base.size);
 	GEM_BUG_ON(!page_size);
diff --git a/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c b/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
index debaf7b..5723525 100644
--- a/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
+++ b/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
@@ -28,7 +28,8 @@ static struct sg_table *mock_map_dma_buf(struct dma_buf_attachment *attachment,
 		sg = sg_next(sg);
 	}
 
-	if (!dma_map_sg(attachment->dev, st->sgl, st->nents, dir)) {
+	st->nents = dma_map_sg(attachment->dev, st->sgl, st->orig_nents, dir);
+	if (!st->nents) {
 		err = -ENOMEM;
 		goto err_st;
 	}
@@ -46,7 +47,7 @@ static void mock_unmap_dma_buf(struct dma_buf_attachment *attachment,
 			       struct sg_table *st,
 			       enum dma_data_direction dir)
 {
-	dma_unmap_sg(attachment->dev, st->sgl, st->nents, dir);
+	dma_unmap_sg(attachment->dev, st->sgl, st->orig_nents, dir);
 	sg_free_table(st);
 	kfree(st);
 }
diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt.c b/drivers/gpu/drm/i915/gt/intel_ggtt.c
index 66165b1..9a298bf 100644
--- a/drivers/gpu/drm/i915/gt/intel_ggtt.c
+++ b/drivers/gpu/drm/i915/gt/intel_ggtt.c
@@ -1221,7 +1221,7 @@ void i915_ggtt_resume(struct i915_ggtt *ggtt)
 	for (column = 0; column < width; column++) {
 		src_idx = stride * (height - 1) + column + offset;
 		for (row = 0; row < height; row++) {
-			st->nents++;
+			st->nents = st->orig_nents = st->nents + 1;
 			/*
 			 * We don't need the pages, but need to initialize
 			 * the entries so the sg list can be happily traversed.
@@ -1259,7 +1259,7 @@ void i915_ggtt_resume(struct i915_ggtt *ggtt)
 	if (ret)
 		goto err_sg_alloc;
 
-	st->nents = 0;
+	st->nents = st->orig_nents = 0;
 	sg = st->sgl;
 
 	for (i = 0 ; i < ARRAY_SIZE(rot_info->plane); i++) {
@@ -1306,7 +1306,7 @@ void i915_ggtt_resume(struct i915_ggtt *ggtt)
 
 			length = min(left, length);
 
-			st->nents++;
+			st->nents = st->orig_nents = st->nents + 1;
 
 			sg_set_page(sg, NULL, length, 0);
 			sg_dma_address(sg) = addr;
@@ -1343,7 +1343,7 @@ void i915_ggtt_resume(struct i915_ggtt *ggtt)
 	if (ret)
 		goto err_sg_alloc;
 
-	st->nents = 0;
+	st->nents = st->orig_nents = 0;
 	sg = st->sgl;
 
 	for (i = 0 ; i < ARRAY_SIZE(rem_info->plane); i++) {
@@ -1389,7 +1389,7 @@ void i915_ggtt_resume(struct i915_ggtt *ggtt)
 	GEM_BUG_ON(!iter);
 
 	sg = st->sgl;
-	st->nents = 0;
+	st->nents = st->orig_nents = 0;
 	do {
 		unsigned int len;
 
@@ -1400,7 +1400,7 @@ void i915_ggtt_resume(struct i915_ggtt *ggtt)
 			sg_dma_address(iter) + (offset << PAGE_SHIFT);
 		sg_dma_len(sg) = len;
 
-		st->nents++;
+		st->nents = st->orig_nents = st->nents + 1;
 		count -= len >> PAGE_SHIFT;
 		if (count == 0) {
 			sg_mark_end(sg);
diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index cb43381..c4122cd3 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -28,10 +28,11 @@ int i915_gem_gtt_prepare_pages(struct drm_i915_gem_object *obj,
 			       struct sg_table *pages)
 {
 	do {
-		if (dma_map_sg_attrs(&obj->base.dev->pdev->dev,
-				     pages->sgl, pages->nents,
-				     PCI_DMA_BIDIRECTIONAL,
-				     DMA_ATTR_NO_WARN))
+		pages->nents = dma_map_sg_attrs(&obj->base.dev->pdev->dev,
+						pages->sgl, pages->orig_nents,
+						PCI_DMA_BIDIRECTIONAL,
+						DMA_ATTR_NO_WARN);
+		if (page->nents)
 			return 0;
 
 		/*
@@ -68,7 +69,8 @@ void i915_gem_gtt_finish_pages(struct drm_i915_gem_object *obj,
 		}
 	}
 
-	dma_unmap_sg(kdev, pages->sgl, pages->nents, PCI_DMA_BIDIRECTIONAL);
+	dma_unmap_sg(kdev, pages->sgl, pages->orig_nents,
+		     PCI_DMA_BIDIRECTIONAL);
 }
 
 /**
diff --git a/drivers/gpu/drm/i915/i915_scatterlist.c b/drivers/gpu/drm/i915/i915_scatterlist.c
index cc6b384..05bee13 100644
--- a/drivers/gpu/drm/i915/i915_scatterlist.c
+++ b/drivers/gpu/drm/i915/i915_scatterlist.c
@@ -15,11 +15,11 @@ bool i915_sg_trim(struct sg_table *orig_st)
 	if (orig_st->nents == orig_st->orig_nents)
 		return false;
 
-	if (sg_alloc_table(&new_st, orig_st->nents, GFP_KERNEL | __GFP_NOWARN))
+	if (sg_alloc_table(&new_st, orig_st->orig_nents, GFP_KERNEL | __GFP_NOWARN))
 		return false;
 
 	new_sg = new_st.sgl;
-	for_each_sg(orig_st->sgl, sg, orig_st->nents, i) {
+	for_each_sg(orig_st->sgl, sg, orig_st->orig_nents, i) {
 		sg_set_page(new_sg, sg_page(sg), sg->length, 0);
 		sg_dma_address(new_sg) = sg_dma_address(sg);
 		sg_dma_len(new_sg) = sg_dma_len(sg);
diff --git a/drivers/gpu/drm/i915/selftests/scatterlist.c b/drivers/gpu/drm/i915/selftests/scatterlist.c
index d599186..4456fe5 100644
--- a/drivers/gpu/drm/i915/selftests/scatterlist.c
+++ b/drivers/gpu/drm/i915/selftests/scatterlist.c
@@ -48,9 +48,9 @@ static noinline int expect_pfn_sg(struct pfn_table *pt,
 	unsigned long pfn, n;
 
 	pfn = pt->start;
-	for_each_sg(pt->st.sgl, sg, pt->st.nents, n) {
+	for_each_sg(pt->st.sgl, sg, pt->st.orig_nents, n) {
 		struct page *page = sg_page(sg);
-		unsigned int npages = npages_fn(n, pt->st.nents, rnd);
+		unsigned int npages = npages_fn(n, pt->st.orig_nents, rnd);
 
 		if (page_to_pfn(page) != pfn) {
 			pr_err("%s: %s left pages out of order, expected pfn %lu, found pfn %lu (using for_each_sg)\n",
@@ -86,7 +86,7 @@ static noinline int expect_pfn_sg_page_iter(struct pfn_table *pt,
 	unsigned long pfn;
 
 	pfn = pt->start;
-	for_each_sg_page(pt->st.sgl, &sgiter, pt->st.nents, 0) {
+	for_each_sg_page(pt->st.sgl, &sgiter, pt->st.orig_nents, 0) {
 		struct page *page = sg_page_iter_page(&sgiter);
 
 		if (page != pfn_to_page(pfn)) {
@@ -256,7 +256,7 @@ static int alloc_table(struct pfn_table *pt,
 		pfn += npages;
 	}
 	sg_mark_end(sg);
-	pt->st.nents = n;
+	pt->st.nents = pt->st.orig_nents = n;
 	pt->end = pfn;
 
 	return 0;
-- 
1.9.1