linux-kernel - [PATCH 3/9] swiotlb: do not panic on mapping failures

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Message-Id: <20180917153826.28052-4-hch@lst.de>
Date:   Mon, 17 Sep 2018 17:38:20 +0200
From:   Christoph Hellwig <hch@....de>
To:     Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Robin Murphy <robin.murphy@....com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: [PATCH 3/9] swiotlb: do not panic on mapping failures

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 swace we can
also remove swiotlb_full entirely as it serves no purpose now.

Signed-off-by: Christoph Hellwig <hch@....de>
---
 kernel/dma/swiotlb.c | 33 +--------------------------------
 1 file changed, 1 insertion(+), 32 deletions(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 26d3af52956f..69bf305ee5f8 100644
--- a/kernel/dma/swiotlb.c
+++ 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);
 
@@ -948,7 +918,6 @@ 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);
-- 
2.18.0