[chrome-os:chromeos-5.4 90/99] kernel/dma/swiotlb.c:665 swiotlb_tbl_map_single() warn: unsigned 'index' is never less than zero.

[kernel test robot <lkp@intel.com>]

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tree:   https://chromium.googlesource.com/chromiumos/third_party/kernel chromeos-5.4
head:   f48859423bcc5a5dc65f30eb1dd540af19cf5ebe
commit: 7220eb41bd99b5deba749d2f809ae08ca701de03 [90/99] BACKPORT: FROMLIST: swiotlb: Refactor swiotlb_tbl_{map,unmap}_single
config: i386-randconfig-m021-20210303 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

smatch warnings:
kernel/dma/swiotlb.c:665 swiotlb_tbl_map_single() warn: unsigned 'index' is never less than zero.

vim +/index +665 kernel/dma/swiotlb.c

   641	
   642	phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
   643					   dma_addr_t tbl_dma_addr,
   644					   phys_addr_t orig_addr,
   645					   size_t mapping_size,
   646					   size_t alloc_size,
   647					   enum dma_data_direction dir,
   648					   unsigned long attrs)
   649	{
   650		struct swiotlb *swiotlb = get_swiotlb(hwdev);
   651		phys_addr_t tlb_addr;
   652		unsigned int nslots, index;
   653		int i;
   654	
   655		if (mem_encrypt_active())
   656			pr_warn_once("Memory encryption is active and system is using DMA bounce buffers\n");
   657	
   658		if (mapping_size > alloc_size) {
   659			dev_warn_once(hwdev, "Invalid sizes (mapping: %zd bytes, alloc: %zd bytes)",
   660				      mapping_size, alloc_size);
   661			return (phys_addr_t)DMA_MAPPING_ERROR;
   662		}
   663	
   664		index = swiotlb_tbl_find_free_region(hwdev, tbl_dma_addr, alloc_size, attrs);
 > 665		if (index < 0)
   666			return (phys_addr_t)DMA_MAPPING_ERROR;
   667	
   668		tlb_addr = swiotlb->start + (index << IO_TLB_SHIFT);
   669	
   670		/*
   671		 * Save away the mapping from the original address to the DMA address.
   672		 * This is needed when we sync the memory.  Then we sync the buffer if
   673		 * needed.
   674		 */
   675		nslots = ALIGN(alloc_size, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;
   676		for (i = 0; i < nslots; i++)
   677			swiotlb->orig_addr[index + i] = orig_addr + (i << IO_TLB_SHIFT);
   678		if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) &&
   679		    (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL))
   680			swiotlb_bounce(orig_addr, tlb_addr, mapping_size, DMA_TO_DEVICE);
   681	
   682		return tlb_addr;
   683	}
   684	

---
0-DAY CI Kernel Test Service, Intel Corporation
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