[v6,21/36] drm: v3d: fix common struct sg_table related issues

Message ID 20200618153956.29558-22-m.szyprowski@samsung.com
State New
Headers show
Series
  • DRM: fix struct sg_table nents vs. orig_nents misuse
Related show

Commit Message

Marek Szyprowski June 18, 2020, 3:39 p.m.
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>

Reviewed-by: Eric Anholt <eric@anholt.net>

---
 drivers/gpu/drm/v3d/v3d_mmu.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

-- 
2.17.1

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Comments

kernel test robot June 18, 2020, 10:28 p.m. | #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: alpha-allyesconfig (attached as .config)
compiler: alpha-linux-gcc (GCC) 9.3.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=alpha 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>, old ones prefixed by <<):

In file included from include/linux/kernel.h:11,
from include/linux/delay.h:22,
from drivers/gpu/drm/v3d/v3d_drv.h:4,
from drivers/gpu/drm/v3d/v3d_mmu.c:21:
drivers/gpu/drm/v3d/v3d_mmu.c: In function 'v3d_mmu_insert_ptes':
include/linux/compiler.h:339:38: error: call to '__compiletime_assert_254' declared with attribute error: BUILD_BUG_ON failed: V3D_MMU_PAGE_SHIFT != PAGE_SIZE
339 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
|                                      ^
include/linux/compiler.h:320:4: note: in definition of macro '__compiletime_assert'
320 |    prefix ## suffix();             |    ^~~~~~
include/linux/compiler.h:339:2: note: in expansion of macro '_compiletime_assert'
339 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
|  ^~~~~~~~~~~~~~~~~~~
include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
|                                     ^~~~~~~~~~~~~~~~~~
include/linux/build_bug.h:50:2: note: in expansion of macro 'BUILD_BUG_ON_MSG'
50 |  BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
|  ^~~~~~~~~~~~~~~~
>> drivers/gpu/drm/v3d/v3d_mmu.c:100:3: note: in expansion of macro 'BUILD_BUG_ON'

100 |   BUILD_BUG_ON(V3D_MMU_PAGE_SHIFT != PAGE_SIZE);
|   ^~~~~~~~~~~~

vim +/BUILD_BUG_ON +100 drivers/gpu/drm/v3d/v3d_mmu.c

    86	
    87	void v3d_mmu_insert_ptes(struct v3d_bo *bo)
    88	{
    89		struct drm_gem_shmem_object *shmem_obj = &bo->base;
    90		struct v3d_dev *v3d = to_v3d_dev(shmem_obj->base.dev);
    91		u32 page = bo->node.start;
    92		u32 page_prot = V3D_PTE_WRITEABLE | V3D_PTE_VALID;
    93		struct sg_dma_page_iter dma_iter;
    94	
    95		for_each_sgtable_dma_page(shmem_obj->sgt, &dma_iter, 0) {
    96			dma_addr_t dma_addr = sg_page_iter_dma_address(&dma_iter);
    97			u32 page_address = dma_addr >> V3D_MMU_PAGE_SHIFT;
    98			u32 pte = page_prot | page_address;
    99	
 > 100			BUILD_BUG_ON(V3D_MMU_PAGE_SHIFT != PAGE_SIZE);

   101			BUG_ON(page_address + 1 >= BIT(24));
   102			v3d->pt[page++] = pte;
   103		}
   104	
   105		WARN_ON_ONCE(page - bo->node.start !=
   106			     shmem_obj->base.size >> V3D_MMU_PAGE_SHIFT);
   107	
   108		if (v3d_mmu_flush_all(v3d))
   109			dev_err(v3d->drm.dev, "MMU flush timeout\n");
   110	}
   111	

---
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Patch

diff --git a/drivers/gpu/drm/v3d/v3d_mmu.c b/drivers/gpu/drm/v3d/v3d_mmu.c
index 3b81ea28c0bb..175c2578ad73 100644
--- a/drivers/gpu/drm/v3d/v3d_mmu.c
+++ b/drivers/gpu/drm/v3d/v3d_mmu.c
@@ -90,19 +90,16 @@  void v3d_mmu_insert_ptes(struct v3d_bo *bo)
 	struct v3d_dev *v3d = to_v3d_dev(shmem_obj->base.dev);
 	u32 page = bo->node.start;
 	u32 page_prot = V3D_PTE_WRITEABLE | V3D_PTE_VALID;
-	unsigned int count;
-	struct scatterlist *sgl;
+	struct sg_dma_page_iter dma_iter;
 
-	for_each_sg(shmem_obj->sgt->sgl, sgl, shmem_obj->sgt->nents, count) {
-		u32 page_address = sg_dma_address(sgl) >> V3D_MMU_PAGE_SHIFT;
+	for_each_sgtable_dma_page(shmem_obj->sgt, &dma_iter, 0) {
+		dma_addr_t dma_addr = sg_page_iter_dma_address(&dma_iter);
+		u32 page_address = dma_addr >> V3D_MMU_PAGE_SHIFT;
 		u32 pte = page_prot | page_address;
-		u32 i;
 
-		BUG_ON(page_address + (sg_dma_len(sgl) >> V3D_MMU_PAGE_SHIFT) >=
-		       BIT(24));
-
-		for (i = 0; i < sg_dma_len(sgl) >> V3D_MMU_PAGE_SHIFT; i++)
-			v3d->pt[page++] = pte + i;
+		BUILD_BUG_ON(V3D_MMU_PAGE_SHIFT != PAGE_SIZE);
+		BUG_ON(page_address + 1 >= BIT(24));
+		v3d->pt[page++] = pte;
 	}
 
 	WARN_ON_ONCE(page - bo->node.start !=