[PATCH 05 of 14] swiotlb: add comment where we handle the overflow ofa dma mask on 32 bit

[Jeremy Fitzhardinge]

From: Ian Campbell <ian.campbell@xxxxxxxxxx>

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
---
 lib/swiotlb.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lib/swiotlb.c b/lib/swiotlb.c
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -301,6 +301,10 @@
 	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);


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