swiotlb: add comment where we handle the overflow of a dma mask on 32…

… bit Impact: cleanup Signed-off-by: Ian Campbell <ian.campbell@citrix.com> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
git-mirror · Dec 17, 2008 · a5ddde4 · a5ddde4
1 parent 0016fde
commit a5ddde4
Showing 1 changed file with 4 additions and 0 deletions.
diff --git a/lib/swiotlb.c b/lib/swiotlb.c
@@ -301,6 +301,10 @@ map_single(struct device *hwdev, char *buffer, size_t size, int dir)
 	start_dma_addr = virt_to_bus(io_tlb_start) & mask;
 
 	offset_slots = ALIGN(start_dma_addr, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;
+
+	/*
+ 	 * Carefully handle integer overflow which can occur when mask == ~0UL.
+ 	 */
 	max_slots = mask + 1
 		    ? ALIGN(mask + 1, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT
 		    : 1UL << (BITS_PER_LONG - IO_TLB_SHIFT);