[PATCH]: PCI: GART iommu alignment fixes [v3]

From: Prarit Bhargava
Date: Wed Jul 23 2008 - 19:55:37 EST

pci_alloc_consistent/dma_alloc_coherent does not return size aligned

>From Documentation/DMA-mapping.txt:

"pci_alloc_consistent returns two values: the virtual address which you
can use to access it from the CPU and dma_handle which you pass to the

The cpu return address and the DMA bus master address are both
guaranteed to be aligned to the smallest PAGE_SIZE order which
is greater than or equal to the requested size. This invariant
exists (for example) to guarantee that if you allocate a chunk
which is smaller than or equal to 64 kilobytes, the extent of the
buffer you receive will not cross a 64K boundary."

1. Modify alloc_iommu to allow for an alignment mask
2. Modify pci_gart_simple to return size-aligned values.
3. Fix possible overflow in alloc_iommu's boundary_size calculation.
(It is possible that alloc_iommu()'s boundary_size overflows as
dma_get_seg_boundary can return 0xffffffff. In that case, further usage of
boundary_size triggers a BUG_ON() in the iommu code.)

End result: When allocating from IOMMU, pci_alloc_consistent/dma_alloc_coherent
will now return a size aligned value.

Signed-off-by: Prarit Bhargava <prarit@xxxxxxxxxx>

diff --git a/arch/x86/kernel/pci-gart_64.c b/arch/x86/kernel/pci-gart_64.c
index faf3229..717ae64 100644
--- a/arch/x86/kernel/pci-gart_64.c
+++ b/arch/x86/kernel/pci-gart_64.c
@@ -83,7 +83,8 @@ AGPEXTERN __u32 *agp_gatt_table;
static unsigned long next_bit; /* protected by iommu_bitmap_lock */
static int need_flush; /* global flush state. set for each gart wrap */

-static unsigned long alloc_iommu(struct device *dev, int size)
+static unsigned long alloc_iommu(struct device *dev, int size,
+ unsigned long mask)
unsigned long offset, flags;
unsigned long boundary_size;
@@ -91,16 +92,17 @@ static unsigned long alloc_iommu(struct device *dev, int size)

base_index = ALIGN(iommu_bus_base & dma_get_seg_boundary(dev),
- boundary_size = ALIGN(dma_get_seg_boundary(dev) + 1,
+ boundary_size = ALIGN((unsigned long long)dma_get_seg_boundary(dev) + 1,

spin_lock_irqsave(&iommu_bitmap_lock, flags);
offset = iommu_area_alloc(iommu_gart_bitmap, iommu_pages, next_bit,
- size, base_index, boundary_size, 0);
+ size, base_index, boundary_size, mask);
if (offset == -1) {
need_flush = 1;
offset = iommu_area_alloc(iommu_gart_bitmap, iommu_pages, 0,
- size, base_index, boundary_size, 0);
+ size, base_index, boundary_size,
+ mask);
if (offset != -1) {
set_bit_string(iommu_gart_bitmap, offset, size);
@@ -240,10 +242,11 @@ nonforced_iommu(struct device *dev, unsigned long addr, size_t size)
* Caller needs to check if the iommu is needed and flush.
static dma_addr_t dma_map_area(struct device *dev, dma_addr_t phys_mem,
- size_t size, int dir)
+ size_t size, int dir, u64 align_mask)
unsigned long npages = to_pages(phys_mem, size);
- unsigned long iommu_page = alloc_iommu(dev, npages);
+ unsigned long palign_mask = align_mask >> PAGE_SHIFT;
+ unsigned long iommu_page = alloc_iommu(dev, npages, palign_mask);
int i;

if (iommu_page == -1) {
@@ -266,7 +269,8 @@ static dma_addr_t dma_map_area(struct device *dev, dma_addr_t phys_mem,
static dma_addr_t
gart_map_simple(struct device *dev, char *buf, size_t size, int dir)
- dma_addr_t map = dma_map_area(dev, virt_to_bus(buf), size, dir);
+ dma_addr_t map = dma_map_area(dev, virt_to_bus(buf), size, dir,
+ size - 1);


@@ -286,7 +290,8 @@ gart_map_single(struct device *dev, void *addr, size_t size, int dir)
if (!need_iommu(dev, phys_mem, size))
return phys_mem;

- bus = gart_map_simple(dev, addr, size, dir);
+ dma_addr_t map = dma_map_area(dev, virt_to_bus(addr), size, dir, 0);
+ flush_gart();

return bus;
@@ -345,7 +350,7 @@ static int dma_map_sg_nonforce(struct device *dev, struct scatterlist *sg,
unsigned long addr = sg_phys(s);

if (nonforced_iommu(dev, addr, s->length)) {
- addr = dma_map_area(dev, addr, s->length, dir);
+ addr = dma_map_area(dev, addr, s->length, dir, 0);
if (addr == bad_dma_address) {
if (i > 0)
gart_unmap_sg(dev, sg, i, dir);
@@ -367,7 +372,7 @@ static int __dma_map_cont(struct device *dev, struct scatterlist *start,
int nelems, struct scatterlist *sout,
unsigned long pages)
- unsigned long iommu_start = alloc_iommu(dev, pages);
+ unsigned long iommu_start = alloc_iommu(dev, pages, 0);
unsigned long iommu_page = iommu_start;
struct scatterlist *s;
int i;
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/