Commit 2db76d7c3c6d ("lib/scatterlist: sg_page_iter: support sg lists w/o
backing pages") introduced the sg_page_iter_dma_address() function without
providing a way to use it in the general case. If the sg_dma_len() is not
equal to the sg length callers cannot safely use the
for_each_sg_page/sg_page_iter_dma_address combination.
Resolve this API mistake by providing a DMA specific iterator,
for_each_sg_dma_page(), that uses the right length so
sg_page_iter_dma_address() works as expected with all sglists.
A new iterator type is introduced to provide compile-time safety against
wrongly mixing accessors and iterators.
Acked-by: Christoph Hellwig <hch@xxxxxx> (for scatterlist)
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
---
.clang-format | 1 +
drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c | 8 +++-
drivers/media/pci/intel/ipu3/ipu3-cio2.c | 4 +-
include/linux/scatterlist.h | 49 ++++++++++++++++++----
lib/scatterlist.c | 26 ++++++++++++
5 files changed, 76 insertions(+), 12 deletions(-)
v2:
- Drop the vmwgfx fix in favor of keeping it unchanged as there is no
reviewer. Use an ugly case with a comment instead.
I'd like to apply this to the RDMA tree next week, a large series from
Shiraz is waiting on it:
https://patchwork.kernel.org/project/linux-rdma/list/?series=71841&state=*
Regards,
Jason
diff --git a/.clang-format b/.clang-format
index bc2ffb2a0b5366..335ce29ab8132c 100644
--- a/.clang-format
+++ b/.clang-format
@@ -240,6 +240,7 @@ ForEachMacros:
- 'for_each_set_bit'
- 'for_each_set_bit_from'
- 'for_each_sg'
+ - 'for_each_sg_dma_page'
- 'for_each_sg_page'
- 'for_each_sibling_event'
- '__for_each_thread'
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
index 31786b200afc47..e84f6aaee778f0 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
@@ -311,7 +311,13 @@ static dma_addr_t __vmw_piter_dma_addr(struct vmw_piter *viter)
static dma_addr_t __vmw_piter_sg_addr(struct vmw_piter *viter)
{
- return sg_page_iter_dma_address(&viter->iter);
+ /*
+ * FIXME: This driver wrongly mixes DMA and CPU SG list iteration and
+ * needs revision. See
+ * https://lore.kernel.org/lkml/20190104223531.GA1705@xxxxxxxx/
+ */
+ return sg_page_iter_dma_address(
+ (struct sg_dma_page_iter *)&viter->iter);
}
diff --git a/drivers/media/pci/intel/ipu3/ipu3-cio2.c b/drivers/media/pci/intel/ipu3/ipu3-cio2.c
index cdb79ae2d8dc72..c0a5ce1d13b0bc 100644
--- a/drivers/media/pci/intel/ipu3/ipu3-cio2.c
+++ b/drivers/media/pci/intel/ipu3/ipu3-cio2.c
@@ -846,7 +846,7 @@ static int cio2_vb2_buf_init(struct vb2_buffer *vb)
unsigned int pages = DIV_ROUND_UP(vb->planes[0].length, CIO2_PAGE_SIZE);
unsigned int lops = DIV_ROUND_UP(pages + 1, entries_per_page);
struct sg_table *sg;
- struct sg_page_iter sg_iter;
+ struct sg_dma_page_iter sg_iter;
int i, j;
if (lops <= 0 || lops > CIO2_MAX_LOPS) {
@@ -873,7 +873,7 @@ static int cio2_vb2_buf_init(struct vb2_buffer *vb)
b->offset = sg->sgl->offset;
i = j = 0;
- for_each_sg_page(sg->sgl, &sg_iter, sg->nents, 0) {
+ for_each_sg_dma_page(sg->sgl, &sg_iter, sg->nents, 0) {
if (!pages--)
break;
b->lop[i][j] = sg_page_iter_dma_address(&sg_iter) >> PAGE_SHIFT;
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index b96f0d0b5b8f30..b4be960c7e5dba 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -339,12 +339,12 @@ int sg_alloc_table_chained(struct sg_table *table, int nents,
/*
* sg page iterator
*
- * Iterates over sg entries page-by-page. On each successful iteration,
- * you can call sg_page_iter_page(@piter) and sg_page_iter_dma_address(@piter)
- * to get the current page and its dma address. @piter->sg will point to the
- * sg holding this page and @piter->sg_pgoffset to the page's page offset
- * within the sg. The iteration will stop either when a maximum number of sg
- * entries was reached or a terminating sg (sg_last(sg) == true) was reached.
+ * Iterates over sg entries page-by-page. On each successful iteration, you
+ * can call sg_page_iter_page(@piter) to get the current page and its dma
+ * address. @piter->sg will point to the sg holding this page and
+ * @piter->sg_pgoffset to the page's page offset within the sg. The iteration
+ * will stop either when a maximum number of sg entries was reached or a
+ * terminating sg (sg_last(sg) == true) was reached.
*/
struct sg_page_iter {
struct scatterlist *sg; /* sg holding the page */
@@ -356,7 +356,19 @@ struct sg_page_iter {
* next step */
};
+/*
+ * sg page iterator for DMA addresses
+ *
+ * This is the same as sg_page_iter however you can call
+ * sg_page_iter_dma_address(@dma_iter) to get the page's DMA
+ * address. sg_page_iter_page() cannot be called on this iterator.
+ */
+struct sg_dma_page_iter {
+ struct sg_page_iter base;
+};
+
bool __sg_page_iter_next(struct sg_page_iter *piter);
+bool __sg_page_iter_dma_next(struct sg_dma_page_iter *dma_iter);
void __sg_page_iter_start(struct sg_page_iter *piter,
struct scatterlist *sglist, unsigned int nents,
unsigned long pgoffset);
@@ -372,11 +384,13 @@ static inline struct page *sg_page_iter_page(struct sg_page_iter *piter)
/**
* sg_page_iter_dma_address - get the dma address of the current page held by
* the page iterator.
- * @piter: page iterator holding the page
+ * @dma_iter: page iterator holding the page
*/
-static inline dma_addr_t sg_page_iter_dma_address(struct sg_page_iter *piter)
+static inline dma_addr_t
+sg_page_iter_dma_address(struct sg_dma_page_iter *dma_iter)
{
- return sg_dma_address(piter->sg) + (piter->sg_pgoffset << PAGE_SHIFT);
+ return sg_dma_address(dma_iter->base.sg) +
+ (dma_iter->base.sg_pgoffset << PAGE_SHIFT);
}
/**
@@ -385,11 +399,28 @@ static inline dma_addr_t sg_page_iter_dma_address(struct sg_page_iter *piter)
* @piter: page iterator to hold current page, sg, sg_pgoffset
* @nents: maximum number of sg entries to iterate over
* @pgoffset: starting page offset
+ *
+ * Callers may use sg_page_iter_page() to get each page pointer.
*/
#define for_each_sg_page(sglist, piter, nents, pgoffset) \
for (__sg_page_iter_start((piter), (sglist), (nents), (pgoffset)); \
__sg_page_iter_next(piter);)
+/**
+ * for_each_sg_dma_page - iterate over the pages of the given sg list
+ * @sglist: sglist to iterate over
+ * @dma_iter: page iterator to hold current page
+ * @dma_nents: maximum number of sg entries to iterate over, this is the value
+ * returned from dma_map_sg
+ * @pgoffset: starting page offset
+ *
+ * Callers may use sg_page_iter_dma_address() to get each page's DMA address.
+ */
+#define for_each_sg_dma_page(sglist, dma_iter, dma_nents, pgoffset) \
+ for (__sg_page_iter_start(&(dma_iter)->base, sglist, dma_nents, \
+ pgoffset); \
+ __sg_page_iter_dma_next(dma_iter);)
+
/*
* Mapping sg iterator
*
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 9ba349e775ef08..739dc9fe2c55ec 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -625,6 +625,32 @@ bool __sg_page_iter_next(struct sg_page_iter *piter)
}
EXPORT_SYMBOL(__sg_page_iter_next);
+static int sg_dma_page_count(struct scatterlist *sg)
+{
+ return PAGE_ALIGN(sg->offset + sg_dma_len(sg)) >> PAGE_SHIFT;
+}
+
+bool __sg_page_iter_dma_next(struct sg_dma_page_iter *dma_iter)
+{
+ struct sg_page_iter *piter = &dma_iter->base;
+
+ if (!piter->__nents || !piter->sg)
+ return false;
+
+ piter->sg_pgoffset += piter->__pg_advance;
+ piter->__pg_advance = 1;
+
+ while (piter->sg_pgoffset >= sg_dma_page_count(piter->sg)) {
+ piter->sg_pgoffset -= sg_dma_page_count(piter->sg);
+ piter->sg = sg_next(piter->sg);
+ if (!--piter->__nents || !piter->sg)
+ return false;
+ }
+
+ return true;
+}
+EXPORT_SYMBOL(__sg_page_iter_dma_next);
+
/**
* sg_miter_start - start mapping iteration over a sg list
* @miter: sg mapping iter to be started
--
2.20.1
