[PATCH v4 32/38] staging: ion: fix common struct sg_table related issues

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

The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function
returns the number of the created entries in the DMA address space.
However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
dma_unmap_sg must be called with the original number of the entries
passed to the dma_map_sg().

struct sg_table is a common structure used for describing a non-contiguous
memory buffer, used commonly in the DRM and graphics subsystems. It
consists of a scatterlist with memory pages and DMA addresses (sgl entry),
as well as the number of scatterlist entries: CPU pages (orig_nents entry)
and DMA mapped pages (nents entry).

It turned out that it was a common mistake to misuse nents and orig_nents
entries, calling DMA-mapping functions with a wrong number of entries or
ignoring the number of mapped entries returned by the dma_map_sg()
function.

To avoid such issues, lets use a common dma-mapping wrappers operating
directly on the struct sg_table objects and use scatterlist page
iterators where possible. This, almost always, hides references to the
nents and orig_nents entries, making the code robust, easier to follow
and copy/paste safe.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
---
For more information, see '[PATCH v4 00/38] DRM: fix struct sg_table nents
vs. orig_nents misuse' thread:
https://lore.kernel.org/dri-devel/20200512085710.14688-1-m.szyprowski@samsung.com/T/
---
 drivers/staging/android/ion/ion.c             | 25 +++++++--------
 drivers/staging/android/ion/ion_heap.c        | 44 ++++++++-------------------
 drivers/staging/android/ion/ion_system_heap.c |  2 +-
 3 files changed, 25 insertions(+), 46 deletions(-)

diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
index 38b51ea..2db041d 100644
--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -147,14 +147,14 @@ static struct sg_table *dup_sg_table(struct sg_table *table)
 	if (!new_table)
 		return ERR_PTR(-ENOMEM);
 
-	ret = sg_alloc_table(new_table, table->nents, GFP_KERNEL);
+	ret = sg_alloc_table(new_table, table->orig_nents, GFP_KERNEL);
 	if (ret) {
 		kfree(new_table);
 		return ERR_PTR(-ENOMEM);
 	}
 
 	new_sg = new_table->sgl;
-	for_each_sg(table->sgl, sg, table->nents, i) {
+	for_each_sgtable_sg(table, sg, i) {
 		memcpy(new_sg, sg, sizeof(*sg));
 		new_sg->dma_address = 0;
 		new_sg = sg_next(new_sg);
@@ -224,12 +224,13 @@ static struct sg_table *ion_map_dma_buf(struct dma_buf_attachment *attachment,
 {
 	struct ion_dma_buf_attachment *a = attachment->priv;
 	struct sg_table *table;
+	int ret;
 
 	table = a->table;
 
-	if (!dma_map_sg(attachment->dev, table->sgl, table->nents,
-			direction))
-		return ERR_PTR(-ENOMEM);
+	ret = dma_map_sgtable(attachment->dev, table, direction);
+	if (ret)
+		return ERR_PTR(ret);
 
 	return table;
 }
@@ -238,7 +239,7 @@ static void ion_unmap_dma_buf(struct dma_buf_attachment *attachment,
 			      struct sg_table *table,
 			      enum dma_data_direction direction)
 {
-	dma_unmap_sg(attachment->dev, table->sgl, table->nents, direction);
+	dma_unmap_sgtable(attachment->dev, table, direction);
 }
 
 static int ion_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
@@ -296,10 +297,8 @@ static int ion_dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
 	}
 
 	mutex_lock(&buffer->lock);
-	list_for_each_entry(a, &buffer->attachments, list) {
-		dma_sync_sg_for_cpu(a->dev, a->table->sgl, a->table->nents,
-				    direction);
-	}
+	list_for_each_entry(a, &buffer->attachments, list)
+		dma_sync_sgtable_for_cpu(a->dev, a->table, direction);
 
 unlock:
 	mutex_unlock(&buffer->lock);
@@ -319,10 +318,8 @@ static int ion_dma_buf_end_cpu_access(struct dma_buf *dmabuf,
 	}
 
 	mutex_lock(&buffer->lock);
-	list_for_each_entry(a, &buffer->attachments, list) {
-		dma_sync_sg_for_device(a->dev, a->table->sgl, a->table->nents,
-				       direction);
-	}
+	list_for_each_entry(a, &buffer->attachments, list)
+		dma_sync_sgtable_for_device(a->dev, a->table, direction);
 	mutex_unlock(&buffer->lock);
 
 	return 0;
diff --git a/drivers/staging/android/ion/ion_heap.c b/drivers/staging/android/ion/ion_heap.c
index 9c23b23..79f2794 100644
--- a/drivers/staging/android/ion/ion_heap.c
+++ b/drivers/staging/android/ion/ion_heap.c
@@ -20,8 +20,7 @@
 void *ion_heap_map_kernel(struct ion_heap *heap,
 			  struct ion_buffer *buffer)
 {
-	struct scatterlist *sg;
-	int i, j;
+	struct sg_page_iter piter;
 	void *vaddr;
 	pgprot_t pgprot;
 	struct sg_table *table = buffer->sg_table;
@@ -38,14 +37,11 @@ void *ion_heap_map_kernel(struct ion_heap *heap,
 	else
 		pgprot = pgprot_writecombine(PAGE_KERNEL);
 
-	for_each_sg(table->sgl, sg, table->nents, i) {
-		int npages_this_entry = PAGE_ALIGN(sg->length) / PAGE_SIZE;
-		struct page *page = sg_page(sg);
-
-		BUG_ON(i >= npages);
-		for (j = 0; j < npages_this_entry; j++)
-			*(tmp++) = page++;
+	for_each_sgtable_page(table, &piter, 0) {
+		BUG_ON(tmp - pages >= npages);
+		*tmp++ = sg_page_iter_page(&piter);
 	}
+
 	vaddr = vmap(pages, npages, VM_MAP, pgprot);
 	vfree(pages);
 
@@ -64,32 +60,19 @@ void ion_heap_unmap_kernel(struct ion_heap *heap,
 int ion_heap_map_user(struct ion_heap *heap, struct ion_buffer *buffer,
 		      struct vm_area_struct *vma)
 {
+	struct sg_page_iter piter;
 	struct sg_table *table = buffer->sg_table;
 	unsigned long addr = vma->vm_start;
-	unsigned long offset = vma->vm_pgoff * PAGE_SIZE;
-	struct scatterlist *sg;
-	int i;
 	int ret;
 
-	for_each_sg(table->sgl, sg, table->nents, i) {
-		struct page *page = sg_page(sg);
-		unsigned long remainder = vma->vm_end - addr;
-		unsigned long len = sg->length;
+	for_each_sgtable_page(table, &piter, vma->vm_pgoff) {
+		struct page *page = sg_page_iter_page(&piter);
 
-		if (offset >= sg->length) {
-			offset -= sg->length;
-			continue;
-		} else if (offset) {
-			page += offset / PAGE_SIZE;
-			len = sg->length - offset;
-			offset = 0;
-		}
-		len = min(len, remainder);
-		ret = remap_pfn_range(vma, addr, page_to_pfn(page), len,
+		ret = remap_pfn_range(vma, addr, page_to_pfn(page), PAGE_SIZE,
 				      vma->vm_page_prot);
 		if (ret)
 			return ret;
-		addr += len;
+		addr += PAGE_SIZE;
 		if (addr >= vma->vm_end)
 			return 0;
 	}
@@ -109,15 +92,14 @@ static int ion_heap_clear_pages(struct page **pages, int num, pgprot_t pgprot)
 	return 0;
 }
 
-static int ion_heap_sglist_zero(struct scatterlist *sgl, unsigned int nents,
-				pgprot_t pgprot)
+static int ion_heap_sglist_zero(struct sg_table *sgt, pgprot_t pgprot)
 {
 	int p = 0;
 	int ret = 0;
 	struct sg_page_iter piter;
 	struct page *pages[32];
 
-	for_each_sg_page(sgl, &piter, nents, 0) {
+	for_each_sgtable_page(sgt, &piter, 0) {
 		pages[p++] = sg_page_iter_page(&piter);
 		if (p == ARRAY_SIZE(pages)) {
 			ret = ion_heap_clear_pages(pages, p, pgprot);
@@ -142,7 +124,7 @@ int ion_heap_buffer_zero(struct ion_buffer *buffer)
 	else
 		pgprot = pgprot_writecombine(PAGE_KERNEL);
 
-	return ion_heap_sglist_zero(table->sgl, table->nents, pgprot);
+	return ion_heap_sglist_zero(table, pgprot);
 }
 
 void ion_heap_freelist_add(struct ion_heap *heap, struct ion_buffer *buffer)
diff --git a/drivers/staging/android/ion/ion_system_heap.c b/drivers/staging/android/ion/ion_system_heap.c
index b83a1d1..eac0632 100644
--- a/drivers/staging/android/ion/ion_system_heap.c
+++ b/drivers/staging/android/ion/ion_system_heap.c
@@ -162,7 +162,7 @@ static void ion_system_heap_free(struct ion_buffer *buffer)
 	if (!(buffer->private_flags & ION_PRIV_FLAG_SHRINKER_FREE))
 		ion_heap_buffer_zero(buffer);
 
-	for_each_sg(table->sgl, sg, table->nents, i)
+	for_each_sgtable_sg(table, sg, i)
 		free_buffer_page(sys_heap, buffer, sg_page(sg));
 	sg_free_table(table);
 	kfree(table);
-- 
1.9.1