From: Christoph Hellwig <hch@lst.de>
Date: Thu, 16 Aug 2018 15:30:39 +0300
Subject: swiotlb: remove the overflow buffer
Git-commit: dff8d6c1ed584de65aac40494d3e7468c50980c3
Patch-mainline: v4.20-rc1
References: bsc#1162171

Like all other dma mapping drivers just return an error code instead
of an actual memory buffer.  The reason for the overflow buffer was
that at the time swiotlb was invented there was no way to check for
dma mapping errors, but this has long been fixed.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Petr Tesarik <ptesarik@suse.com>
Acked-by: Joerg Roedel <jroedel@suse.de>
---
 arch/arm64/mm/dma-mapping.c       |  2 +-
 arch/powerpc/kernel/dma-swiotlb.c |  4 +--
 include/linux/dma-direct.h        |  2 ++
 include/linux/swiotlb.h           |  3 --
 kernel/dma/direct.c               |  2 --
 kernel/dma/swiotlb.c              | 59 ++-------------------------------------
 6 files changed, 8 insertions(+), 64 deletions(-)

--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -70,13 +70,6 @@ static phys_addr_t io_tlb_start, io_tlb_
 static unsigned long io_tlb_nslabs;
 
 /*
- * When the IOMMU overflows we return a fallback buffer. This sets the size.
- */
-static unsigned long io_tlb_overflow = 32*1024;
-
-static phys_addr_t io_tlb_overflow_buffer;
-
-/*
  * This is a free list describing the number of free entries available from
  * each index
  */
@@ -123,7 +116,6 @@ setup_io_tlb_npages(char *str)
 	return 0;
 }
 early_param("swiotlb", setup_io_tlb_npages);
-/* make io_tlb_overflow tunable too? */
 
 unsigned long swiotlb_nr_tbl(void)
 {
@@ -211,16 +203,10 @@ void __init swiotlb_update_mem_attribute
 	bytes = PAGE_ALIGN(io_tlb_nslabs << IO_TLB_SHIFT);
 	swiotlb_set_mem_attributes(vaddr, bytes);
 	memset(vaddr, 0, bytes);
-
-	vaddr = phys_to_virt(io_tlb_overflow_buffer);
-	bytes = PAGE_ALIGN(io_tlb_overflow);
-	swiotlb_set_mem_attributes(vaddr, bytes);
-	memset(vaddr, 0, bytes);
 }
 
 int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
 {
-	void *v_overflow_buffer;
 	unsigned long i, bytes;
 
 	bytes = nslabs << IO_TLB_SHIFT;
@@ -230,17 +216,6 @@ int __init swiotlb_init_with_tbl(char *t
 	io_tlb_end = io_tlb_start + bytes;
 
 	/*
-	 * Get the overflow emergency buffer
-	 */
-	v_overflow_buffer = memblock_virt_alloc_low_nopanic(
-						PAGE_ALIGN(io_tlb_overflow),
-						PAGE_SIZE);
-	if (!v_overflow_buffer)
-		return -ENOMEM;
-
-	io_tlb_overflow_buffer = __pa(v_overflow_buffer);
-
-	/*
 	 * Allocate and initialize the free list array.  This array is used
 	 * to find contiguous free memory regions of size up to IO_TLB_SEGSIZE
 	 * between io_tlb_start and io_tlb_end.
@@ -347,7 +322,6 @@ int
 swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
 {
 	unsigned long i, bytes;
-	unsigned char *v_overflow_buffer;
 
 	bytes = nslabs << IO_TLB_SHIFT;
 
@@ -359,18 +333,6 @@ swiotlb_late_init_with_tbl(char *tlb, un
 	memset(tlb, 0, bytes);
 
 	/*
-	 * Get the overflow emergency buffer
-	 */
-	v_overflow_buffer = (void *)__get_free_pages(GFP_DMA,
-						     get_order(io_tlb_overflow));
-	if (!v_overflow_buffer)
-		goto cleanup2;
-
-	swiotlb_set_mem_attributes(v_overflow_buffer, io_tlb_overflow);
-	memset(v_overflow_buffer, 0, io_tlb_overflow);
-	io_tlb_overflow_buffer = virt_to_phys(v_overflow_buffer);
-
-	/*
 	 * Allocate and initialize the free list array.  This array is used
 	 * to find contiguous free memory regions of size up to IO_TLB_SEGSIZE
 	 * between io_tlb_start and io_tlb_end.
@@ -406,10 +368,6 @@ cleanup4:
 	                                                 sizeof(int)));
 	io_tlb_list = NULL;
 cleanup3:
-	free_pages((unsigned long)v_overflow_buffer,
-		   get_order(io_tlb_overflow));
-	io_tlb_overflow_buffer = 0;
-cleanup2:
 	io_tlb_end = 0;
 	io_tlb_start = 0;
 	io_tlb_nslabs = 0;
@@ -423,8 +381,6 @@ void __init swiotlb_free(void)
 		return;
 
 	if (late_alloc) {
-		free_pages((unsigned long)phys_to_virt(io_tlb_overflow_buffer),
-			   get_order(io_tlb_overflow));
 		free_pages((unsigned long)io_tlb_orig_addr,
 			   get_order(io_tlb_nslabs * sizeof(phys_addr_t)));
 		free_pages((unsigned long)io_tlb_list, get_order(io_tlb_nslabs *
@@ -432,8 +388,6 @@ void __init swiotlb_free(void)
 		free_pages((unsigned long)phys_to_virt(io_tlb_start),
 			   get_order(io_tlb_nslabs << IO_TLB_SHIFT));
 	} else {
-		memblock_free_late(io_tlb_overflow_buffer,
-				   PAGE_ALIGN(io_tlb_overflow));
 		memblock_free_late(__pa(io_tlb_orig_addr),
 				   PAGE_ALIGN(io_tlb_nslabs * sizeof(phys_addr_t)));
 		memblock_free_late(__pa(io_tlb_list),
@@ -828,7 +782,7 @@ dma_addr_t swiotlb_map_page(struct devic
 	/* Oh well, have to allocate and map a bounce buffer. */
 	map = map_single(dev, phys, size, dir, attrs);
 	if (map == SWIOTLB_MAP_ERROR)
-		return swiotlb_phys_to_dma(dev, io_tlb_overflow_buffer);
+		return (dma_addr_t)SWIOTLB_MAP_ERROR;
 
 	dev_addr = swiotlb_phys_to_dma(dev, map);
 
@@ -839,7 +793,7 @@ dma_addr_t swiotlb_map_page(struct devic
 	attrs |= DMA_ATTR_SKIP_CPU_SYNC;
 	swiotlb_tbl_unmap_single(dev, map, size, dir, attrs);
 
-	return swiotlb_phys_to_dma(dev, io_tlb_overflow_buffer);
+	return (dma_addr_t)SWIOTLB_MAP_ERROR;
 }
 EXPORT_SYMBOL_GPL(swiotlb_map_page);
 
@@ -1040,7 +994,7 @@ EXPORT_SYMBOL(swiotlb_sync_sg_for_device
 int
 swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t dma_addr)
 {
-	return (dma_addr == swiotlb_phys_to_dma(hwdev, io_tlb_overflow_buffer));
+	return (dma_addr == (dma_addr_t)SWIOTLB_MAP_ERROR);
 }
 EXPORT_SYMBOL(swiotlb_dma_mapping_error);