Re: [PATCH 4.19 105/306] swiotlb: do not panic on mapping failures

On Wed 2019-11-27 21:29:15, Greg Kroah-Hartman wrote:

From: Christoph Hellwig hch@lst.de

[ Upstream commit 8088546832aa2c0d8f99dd56edf6384f8a9b63b3 ]

All properly written drivers now have error handling in the dma_map_single / dma_map_page callers. As swiotlb_tbl_map_single already prints a useful warning when running out of swiotlb pool space we can also remove swiotlb_full entirely as it serves no purpose now.

Umm. I trust you that is true in mainline, but is it also true for -stable kernels?

Does this fix anything for -stable users?

Best regards, Pavel

+++ b/kernel/dma/swiotlb.c @@ -761,34 +761,6 @@ static bool swiotlb_free_buffer(struct device *dev, size_t size, return true; } -static void -swiotlb_full(struct device *dev, size_t size, enum dma_data_direction dir,

•     int do_panic)
  

-{

• if (swiotlb_force == SWIOTLB_NO_FORCE)

• return;
  

• /*

• * Ran out of IOMMU space for this operation. This is very bad.
  

• * Unfortunately the drivers cannot handle this operation properly.
  

• * unless they check for dma_mapping_error (most don't)
  

• * When the mapping is small enough return a static buffer to limit
  

• * the damage, or panic when the transfer is too big.
  

• */
  

• dev_err_ratelimited(dev, "DMA: Out of SW-IOMMU space for %zu bytes\n",

• 	    size);
  

• if (size <= io_tlb_overflow || !do_panic)

• return;
  

• if (dir == DMA_BIDIRECTIONAL)

• panic("DMA: Random memory could be DMA accessed\n");
  

• if (dir == DMA_FROM_DEVICE)

• panic("DMA: Random memory could be DMA written\n");
  

• if (dir == DMA_TO_DEVICE)

• panic("DMA: Random memory could be DMA read\n");
  

-}

/*

• Map a single buffer of the indicated size for DMA in streaming mode. The
• physical address to use is returned.

@@ -817,10 +789,8 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page, /* Oh well, have to allocate and map a bounce buffer. */ map = map_single(dev, phys, size, dir, attrs);

• if (map == SWIOTLB_MAP_ERROR) {

• swiotlb_full(dev, size, dir, 1);
  

• if (map == SWIOTLB_MAP_ERROR) return __phys_to_dma(dev, io_tlb_overflow_buffer);

• }

dev_addr = __phys_to_dma(dev, map); @@ -954,7 +924,6 @@ swiotlb_map_sg_attrs(struct device *hwdev, struct scatterlist *sgl, int nelems, if (map == SWIOTLB_MAP_ERROR) { /* Don't panic here, we expect map_sg users to do proper error handling. */

• 		swiotlb_full(hwdev, sg->length, dir, 0);
  	attrs |= DMA_ATTR_SKIP_CPU_SYNC;
  	swiotlb_unmap_sg_attrs(hwdev, sgl, i, dir,
  			       attrs);