dma-mapping: introduce dma_get_seg_boundary_nr_pages()
We found that callers of dma_get_seg_boundary mostly do an ALIGN
with page mask and then do a page shift to get number of pages:
ALIGN(boundary + 1, 1 << shift) >> shift
However, the boundary might be as large as ULONG_MAX, which means
that a device has no specific boundary limit. So either "+ 1" or
passing it to ALIGN() would potentially overflow.
According to kernel defines:
#define ALIGN_MASK(x, mask) (((x) + (mask)) & ~(mask))
#define ALIGN(x, a) ALIGN_MASK(x, (typeof(x))(a) - 1)
We can simplify the logic here into a helper function doing:
ALIGN(boundary + 1, 1 << shift) >> shift
= ALIGN_MASK(b + 1, (1 << s) - 1) >> s
= {[b + 1 + (1 << s) - 1] & ~[(1 << s) - 1]} >> s
= [b + 1 + (1 << s) - 1] >> s
= [b + (1 << s)] >> s
= (b >> s) + 1
This patch introduces and applies dma_get_seg_boundary_nr_pages()
as an overflow-free helper for the dma_get_seg_boundary() callers
to get numbers of pages. It also takes care of the NULL dev case
for non-DMA API callers.
Suggested-by: Christoph Hellwig <[email protected]>
Signed-off-by: Nicolin Chen <[email protected]>
Acked-by: Niklas Schnelle <[email protected]>
Acked-by: Michael Ellerman <[email protected]> (powerpc)
Signed-off-by: Christoph Hellwig <[email protected]>
diff --git a/arch/s390/pci/pci_dma.c b/arch/s390/pci/pci_dma.c
index 64b1399..4a37d8f 100644
--- a/arch/s390/pci/pci_dma.c
+++ b/arch/s390/pci/pci_dma.c
@@ -261,13 +261,11 @@ static unsigned long __dma_alloc_iommu(struct device *dev,
unsigned long start, int size)
{
struct zpci_dev *zdev = to_zpci(to_pci_dev(dev));
- unsigned long boundary_size;
- boundary_size = ALIGN(dma_get_seg_boundary(dev) + 1,
- PAGE_SIZE) >> PAGE_SHIFT;
return iommu_area_alloc(zdev->iommu_bitmap, zdev->iommu_pages,
start, size, zdev->start_dma >> PAGE_SHIFT,
- boundary_size, 0);
+ dma_get_seg_boundary_nr_pages(dev, PAGE_SHIFT),
+ 0);
}
static dma_addr_t dma_alloc_address(struct device *dev, int size)
