Re: [Linaro-mm-sig] [v2 4/4] ARM: dma-mapping: IOMMU allocates pages from atomic_pool with GFP_ATOMIC

Hi Hiroshi,

On Thursday, August 23, 2012 8:10 AM Hiroshi Doyu wrote:

Makes use of the same atomic pool from DMA, and skips kernel page mapping which can involve sleep'able operations at allocating a kernel page table.

Signed-off-by: Hiroshi Doyu hdoyu@nvidia.com

arch/arm/mm/dma-mapping.c | 30 +++++++++++++++++++++++++----- 1 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c index 7ab016b..433312a 100644 --- a/arch/arm/mm/dma-mapping.c +++ b/arch/arm/mm/dma-mapping.c @@ -1063,7 +1063,6 @@ static struct page **__iommu_alloc_buffer(struct device *dev, size_t size, struct page **pages; int count = size >> PAGE_SHIFT; int array_size = count * sizeof(struct page *);

• int err;

  if ((array_size <= PAGE_SIZE) || (gfp & GFP_ATOMIC)) pages = kzalloc(array_size, gfp);

@@ -1072,9 +1071,20 @@ static struct page **__iommu_alloc_buffer(struct device *dev, size_t size, if (!pages) return NULL;

• err = __alloc_fill_pages(&pages, count, gfp);
• if (err)

• goto error
  

• if (gfp & GFP_ATOMIC) {

• struct page *page;
  

• int i;
  

• void *addr = __alloc_from_pool(size, &page);
  

• if (!addr)
  

• 	goto error;
  

• for (i = 0; i < count; i++)
  

• 	pages[i] = page + i;
  

• } else {

• int err = __alloc_fill_pages(&pages, count, gfp);
  

• if (err)
  

• 	goto error;
  

• }

  return pages;

@@ -1091,9 +1101,15 @@ static int __iommu_free_buffer(struct device *dev, struct page **pages, size_t s int count = size >> PAGE_SHIFT; int array_size = count * sizeof(struct page *); int i;

• if (__free_from_pool(page_address(pages[0]), size))

• goto out;
  

• for (i = 0; i < count; i++) if (pages[i]) __free_pages(pages[i], 0);

+out: if ((array_size <= PAGE_SIZE) || __in_atomic_pool(page_address(pages[0]), size)) kfree(pages); @@ -1221,6 +1237,9 @@ static void *arm_iommu_alloc_attrs(struct device *dev, size_t size, if (*handle == DMA_ERROR_CODE) goto err_buffer;

• if (gfp & GFP_ATOMIC)

• return page_address(pages[0]);
  

• if (dma_get_attr(DMA_ATTR_NO_KERNEL_MAPPING, attrs)) return pages;

I've read the whole code and it looks that it starts to become a little spaghetti - there are too many places altered by those atomic changes and it is hard to follow the logic at the first sight.

IMHO it will be better to add a following function:

static void *__iommu_alloc_atomic(struct device *dev, size_t size, dma_addr_t *handle) { struct page *page, **pages; int count = size >> PAGE_SHIFT; int array_size = count * sizeof(struct page *); void *addr; int i;

pages = kzalloc(array_size, gfp); if (!pages) return NULL;

addr = __alloc_from_pool(size, &page); if (!addr) goto err_pool;

for (i = 0; i < count; i++) pages[i] = page + i;

*handle = __iommu_create_mapping(dev, pages, size); if (*handle == DMA_ERROR_CODE) goto err_mapping;

return addr;

err_mapping: __free_from_pool(addr, size); err_pool: kfree(pages); return NULL; }

and then call it at the beginning of the arm_iommu_alloc_attrs():

if (gfp & GFP_ATOMIC) return __iommu_alloc_atomic(dev, size, handle);

You should also add support for the allocation from atomic_pool to __iommu_get_pages() function to get dma_mmap() and dma_get_sgtable() working correctly.

@@ -1279,7 +1298,8 @@ void arm_iommu_free_attrs(struct device *dev, size_t size, void *cpu_addr, return; }

• if (!dma_get_attr(DMA_ATTR_NO_KERNEL_MAPPING, attrs)) {

• if (!dma_get_attr(DMA_ATTR_NO_KERNEL_MAPPING, attrs) ||

•    !__in_atomic_pool(cpu_addr, size)) {
  

  unmap_kernel_range((unsigned long)cpu_addr, size); vunmap(cpu_addr); }

Are you sure this one works? __iommu_get_pages() won't find pages array, because atomic allocations don't get their separate vm_struct area, so this check will be never reached. Maybe a __iommu_free_atomic() function would also make it safer and easier to understand.

Best regards