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

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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>
This commit is contained in:
Ian Campbell 2008-12-16 12:17:29 -08:00 committed by Ingo Molnar
parent 0016fdee92
commit a5ddde4a55
1 changed files with 4 additions and 0 deletions
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4
lib/swiotlb.c
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@ -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; start_dma_addr = virt_to_bus(io_tlb_start) & mask;
offset_slots = ALIGN(start_dma_addr, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT; 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 max_slots = mask + 1
? ALIGN(mask + 1, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT ? ALIGN(mask + 1, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT
: 1UL << (BITS_PER_LONG - IO_TLB_SHIFT); : 1UL << (BITS_PER_LONG - IO_TLB_SHIFT);