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 <[email protected]>
Acked-by: Roland Scheidegger <[email protected]>
---
drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c | 17 ++++-------------
1 file changed, 4 insertions(+), 13 deletions(-)
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
index bf0bc4697959..49ed6add6969 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
@@ -362,8 +362,7 @@ static void vmw_ttm_unmap_from_dma(struct vmw_ttm_tt *vmw_tt)
{
struct device *dev = vmw_tt->dev_priv->dev->dev;
- dma_unmap_sg(dev, vmw_tt->sgt.sgl, vmw_tt->sgt.nents,
- DMA_BIDIRECTIONAL);
+ dma_unmap_sgtable(dev, vmw_tt->sgt, DMA_BIDIRECTIONAL, 0);
vmw_tt->sgt.nents = vmw_tt->sgt.orig_nents;
}
@@ -383,16 +382,8 @@ static void vmw_ttm_unmap_from_dma(struct vmw_ttm_tt *vmw_tt)
static int vmw_ttm_map_for_dma(struct vmw_ttm_tt *vmw_tt)
{
struct device *dev = vmw_tt->dev_priv->dev->dev;
- int ret;
-
- ret = dma_map_sg(dev, vmw_tt->sgt.sgl, vmw_tt->sgt.orig_nents,
- DMA_BIDIRECTIONAL);
- if (unlikely(ret == 0))
- return -ENOMEM;
- vmw_tt->sgt.nents = ret;
-
- return 0;
+ return dma_map_sgtable(dev, vmw_tt->sgt, DMA_BIDIRECTIONAL, 0);
}
/**
@@ -449,10 +440,10 @@ static int vmw_ttm_map_dma(struct vmw_ttm_tt *vmw_tt)
if (unlikely(ret != 0))
goto out_sg_alloc_fail;
- if (vsgt->num_pages > vmw_tt->sgt.nents) {
+ if (vsgt->num_pages > vmw_tt->sgt.orig_nents) {
uint64_t over_alloc =
sgl_size * (vsgt->num_pages -
- vmw_tt->sgt.nents);
+ vmw_tt->sgt.orig_nents);
ttm_mem_global_free(glob, over_alloc);
vmw_tt->sg_alloc_size -= over_alloc;
--
2.17.1
Hi Marek,
I love your patch! Perhaps something to improve:
[auto build test WARNING on next-20200618]
[also build test WARNING on v5.8-rc1]
[cannot apply to linuxtv-media/master staging/staging-testing drm-exynos/exynos-drm-next drm-intel/for-linux-next linus/master v5.8-rc1 v5.7 v5.7-rc7]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use as documented in
https://git-scm.com/docs/git-format-patch]
url: https://github.com/0day-ci/linux/commits/Marek-Szyprowski/DRM-fix-struct-sg_table-nents-vs-orig_nents-misuse/20200619-000417
base: ce2cc8efd7a40cbd17841add878cb691d0ce0bba
config: x86_64-randconfig-s021-20200618 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-13) 9.3.0
reproduce:
# apt-get install sparse
# sparse version: v0.6.2-rc1-10-gc17b1b06-dirty
# save the attached .config to linux build tree
make W=1 C=1 ARCH=x86_64 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__'
If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <[email protected]>
sparse warnings: (new ones prefixed by >>)
>> drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c:365:38: sparse: sparse: incorrect type in argument 2 (different base types) @@ expected struct sg_table *sgt @@ got struct sg_table sgt @@
>> drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c:365:38: sparse: expected struct sg_table *sgt
>> drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c:365:38: sparse: got struct sg_table sgt
drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c:386:43: sparse: sparse: incorrect type in argument 2 (different base types) @@ expected struct sg_table *sgt @@ got struct sg_table sgt @@
drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c:386:43: sparse: expected struct sg_table *sgt
drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c:386:43: sparse: got struct sg_table sgt
vim +365 drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
352
353 /**
354 * vmw_ttm_unmap_from_dma - unmap device addresses previsouly mapped for
355 * TTM pages
356 *
357 * @vmw_tt: Pointer to a struct vmw_ttm_backend
358 *
359 * Used to free dma mappings previously mapped by vmw_ttm_map_for_dma.
360 */
361 static void vmw_ttm_unmap_from_dma(struct vmw_ttm_tt *vmw_tt)
362 {
363 struct device *dev = vmw_tt->dev_priv->dev->dev;
364
> 365 dma_unmap_sgtable(dev, vmw_tt->sgt, DMA_BIDIRECTIONAL, 0);
366 vmw_tt->sgt.nents = vmw_tt->sgt.orig_nents;
367 }
368
---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/[email protected]
Hi Marek,
I love your patch! Yet something to improve:
[auto build test ERROR on next-20200618]
[also build test ERROR on v5.8-rc1]
[cannot apply to linuxtv-media/master staging/staging-testing drm-exynos/exynos-drm-next drm-intel/for-linux-next linus/master v5.8-rc1 v5.7 v5.7-rc7]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use as documented in
https://git-scm.com/docs/git-format-patch]
url: https://github.com/0day-ci/linux/commits/Marek-Szyprowski/DRM-fix-struct-sg_table-nents-vs-orig_nents-misuse/20200619-000417
base: ce2cc8efd7a40cbd17841add878cb691d0ce0bba
config: x86_64-rhel-7.6 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-13) 9.3.0
reproduce (this is a W=1 build):
# save the attached .config to linux build tree
make W=1 ARCH=x86_64
If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <[email protected]>
All error/warnings (new ones prefixed by >>):
drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c: In function 'vmw_ttm_unmap_from_dma':
>> drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c:365:31: error: incompatible type for argument 2 of 'dma_unmap_sgtable'
365 | dma_unmap_sgtable(dev, vmw_tt->sgt, DMA_BIDIRECTIONAL, 0);
| ~~~~~~^~~~~
| |
| struct sg_table
In file included from include/linux/dma-buf.h:20,
from drivers/gpu/drm/vmwgfx/ttm_object.h:40,
from drivers/gpu/drm/vmwgfx/ttm_lock.h:55,
from drivers/gpu/drm/vmwgfx/vmwgfx_drv.h:44,
from drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c:28:
include/linux/dma-mapping.h:651:75: note: expected 'struct sg_table *' but argument is of type 'struct sg_table'
651 | static inline void dma_unmap_sgtable(struct device *dev, struct sg_table *sgt,
| ~~~~~~~~~~~~~~~~~^~~
drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c: In function 'vmw_ttm_map_for_dma':
>> drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c:386:36: error: incompatible type for argument 2 of 'dma_map_sgtable'
386 | return dma_map_sgtable(dev, vmw_tt->sgt, DMA_BIDIRECTIONAL, 0);
| ~~~~~~^~~~~
| |
| struct sg_table
In file included from include/linux/dma-buf.h:20,
from drivers/gpu/drm/vmwgfx/ttm_object.h:40,
from drivers/gpu/drm/vmwgfx/ttm_lock.h:55,
from drivers/gpu/drm/vmwgfx/vmwgfx_drv.h:44,
from drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c:28:
include/linux/dma-mapping.h:628:72: note: expected 'struct sg_table *' but argument is of type 'struct sg_table'
628 | static inline int dma_map_sgtable(struct device *dev, struct sg_table *sgt,
| ~~~~~~~~~~~~~~~~~^~~
>> drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c:387:1: warning: control reaches end of non-void function [-Wreturn-type]
387 | }
| ^
vim +/dma_unmap_sgtable +365 drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
352
353 /**
354 * vmw_ttm_unmap_from_dma - unmap device addresses previsouly mapped for
355 * TTM pages
356 *
357 * @vmw_tt: Pointer to a struct vmw_ttm_backend
358 *
359 * Used to free dma mappings previously mapped by vmw_ttm_map_for_dma.
360 */
361 static void vmw_ttm_unmap_from_dma(struct vmw_ttm_tt *vmw_tt)
362 {
363 struct device *dev = vmw_tt->dev_priv->dev->dev;
364
> 365 dma_unmap_sgtable(dev, vmw_tt->sgt, DMA_BIDIRECTIONAL, 0);
366 vmw_tt->sgt.nents = vmw_tt->sgt.orig_nents;
367 }
368
369 /**
370 * vmw_ttm_map_for_dma - map TTM pages to get device addresses
371 *
372 * @vmw_tt: Pointer to a struct vmw_ttm_backend
373 *
374 * This function is used to get device addresses from the kernel DMA layer.
375 * However, it's violating the DMA API in that when this operation has been
376 * performed, it's illegal for the CPU to write to the pages without first
377 * unmapping the DMA mappings, or calling dma_sync_sg_for_cpu(). It is
378 * therefore only legal to call this function if we know that the function
379 * dma_sync_sg_for_cpu() is a NOP, and dma_sync_sg_for_device() is at most
380 * a CPU write buffer flush.
381 */
382 static int vmw_ttm_map_for_dma(struct vmw_ttm_tt *vmw_tt)
383 {
384 struct device *dev = vmw_tt->dev_priv->dev->dev;
385
> 386 return dma_map_sgtable(dev, vmw_tt->sgt, DMA_BIDIRECTIONAL, 0);
> 387 }
388
---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/[email protected]