avoid endless loops in lib/swiotlb.c

@@ -310,7 +310,9 @@ map_single(struct device *hwdev, char *b
 	start_dma_addr = virt_to_bus(io_tlb_start) & mask;
 
 	offset_slots = ALIGN(start_dma_addr, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;
-	max_slots = ALIGN(mask + 1, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;
+	max_slots = mask + 1
+		    ? ALIGN(mask + 1, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT
+		    : 1UL << (BITS_PER_LONG - IO_TLB_SHIFT);
 
 	/*
 	 * For mappings greater than a page, we limit the stride (and

@@ -333,16 +335,18 @@ map_single(struct device *hwdev, char *b
 		index = ALIGN(io_tlb_index, stride);
 		if (index >= io_tlb_nslabs)
 			index = 0;
-
-		while (is_span_boundary(index, nslots, offset_slots,
-					max_slots)) {
-			index += stride;
-			if (index >= io_tlb_nslabs)
-				index = 0;
-		}
 		wrap = index;
 
 		do {
+			while (is_span_boundary(index, nslots, offset_slots,
+						max_slots)) {
+				index += stride;
+				if (index >= io_tlb_nslabs)
+					index = 0;
+				if (index == wrap)
+					goto not_found;
+			}
+
 			/*
 			 * If we find a slot that indicates we have 'nslots'
 			 * number of contiguous buffers, we allocate the

@@ -367,14 +371,12 @@ map_single(struct device *hwdev, char *b
 
 				goto found;
 			}
-			do {
-				index += stride;
-				if (index >= io_tlb_nslabs)
-					index = 0;
-			} while (is_span_boundary(index, nslots, offset_slots,
-						  max_slots));
+			index += stride;
+			if (index >= io_tlb_nslabs)
+				index = 0;
 		} while (index != wrap);
 
+  not_found:
 		spin_unlock_irqrestore(&io_tlb_lock, flags);
 		return NULL;
 	}

index 4bb5a11..2c6392a 100644
@@ -31,6 +31,7 @@
 
 #include <linux/init.h>
 #include <linux/bootmem.h>
+#include <linux/iommu-helper.h>
 
 #define OFFSET(val,align) ((unsigned long)	\
 	                   ( (val) & ( (align) - 1)))

@@ -282,15 +283,6 @@ address_needs_mapping(struct device *hwdev, dma_addr_t addr)
 	return (addr & ~mask) != 0;
 }
 
-static inline unsigned int is_span_boundary(unsigned int index,
-					    unsigned int nslots,
-					    unsigned long offset_slots,
-					    unsigned long max_slots)
-{
-	unsigned long offset = (offset_slots + index) & (max_slots - 1);
-	return offset + nslots > max_slots;
-}
-
 /*
  * Allocates bounce buffer and returns its kernel virtual address.
  */

@@ -334,8 +326,8 @@ map_single(struct device *hwdev, char *buffer, size_t size, int dir)
 		if (index >= io_tlb_nslabs)
 			index = 0;
 
-		while (is_span_boundary(index, nslots, offset_slots,
-					max_slots)) {
+		while (iommu_is_span_boundary(index, nslots, offset_slots,
+					      max_slots)) {
 			index += stride;
 			if (index >= io_tlb_nslabs)
 				index = 0;

@@ -371,8 +363,9 @@ map_single(struct device *hwdev, char *buffer, size_t size, int dir)
 				index += stride;
 				if (index >= io_tlb_nslabs)
 					index = 0;
-			} while (is_span_boundary(index, nslots, offset_slots,
-						  max_slots));
+			} while (iommu_is_span_boundary(index, nslots,
+							offset_slots,
+							max_slots));
 		} while (index != wrap);
 
 		spin_unlock_irqrestore(&io_tlb_lock, flags);