Don't touch the non DMA members in the sg list in dma_map_sg in the IOMMU

Some drivers (in particular ST) ran into problems because they
reused the sg lists after passing them to pci_map_sg(). The merging
procedure in the K8 GART IOMMU corrupted the state. This patch
changes it to only touch the dma* entries during merging,
but not the other fields.  Approach suggested by Dave Miller.

I did some basic tests with CONFIG_IOMMU_DEBUG (LTP, large dd) 
and without and it hold up, but needs more testing.

Signed-off-by: Andi Kleen <ak@suse.de>

---
 arch/x86_64/kernel/pci-gart.c |    6 ++----
 1 files changed, 2 insertions(+), 4 deletions(-)

Index: linux/arch/x86_64/kernel/pci-gart.c
===================================================================
--- linux.orig/arch/x86_64/kernel/pci-gart.c
+++ linux/arch/x86_64/kernel/pci-gart.c
@@ -300,7 +300,7 @@ void gart_unmap_sg(struct device *dev, s
 
 	for (i = 0; i < nents; i++) {
 		struct scatterlist *s = &sg[i];
-		if (!s->dma_length || !s->length)
+		if (!s->dma_length)
 			break;
 		dma_unmap_single(dev, s->dma_address, s->dma_length, dir);
 	}
@@ -354,7 +354,6 @@ static int __dma_map_cont(struct scatter
 		
 		BUG_ON(i > start && s->offset);
 		if (i == start) {
-			*sout = *s; 
 			sout->dma_address = iommu_bus_base;
 			sout->dma_address += iommu_page*PAGE_SIZE + s->offset;
 			sout->dma_length = s->length;
@@ -369,7 +368,7 @@ static int __dma_map_cont(struct scatter
 			SET_LEAK(iommu_page);
 			addr += PAGE_SIZE;
 			iommu_page++;
-	} 
+		} 
 	} 
 	BUG_ON(iommu_page - iommu_start != pages);	
 	return 0;
@@ -381,7 +380,6 @@ static inline int dma_map_cont(struct sc
 {
 	if (!need) { 
 		BUG_ON(stopat - start != 1);
-		*sout = sg[start]; 
 		sout->dma_length = sg[start].length; 
 		return 0;
 	}