[PATCH V2 2/3] Add swiotlb offset preserving mapping when dma_dma_parameters->page_offset_mask is non zero.

[Jianxiong Gao]

For devices that need to preserve address offset on mapping through
swiotlb, this patch adds offset preserving based on page_offset_mask
and keeps the offset if the mask is non zero. This is needed for
device drivers like NVMe.

Signed-off-by: Jianxiong Gao <jxgao at google.com>
---
 kernel/dma/swiotlb.c | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 7c42df6e6100..eeb640df35f3 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -468,7 +468,7 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev, phys_addr_t orig_addr,
 	dma_addr_t tbl_dma_addr = phys_to_dma_unencrypted(hwdev, io_tlb_start);
 	unsigned long flags;
 	phys_addr_t tlb_addr;
-	unsigned int nslots, stride, index, wrap;
+	unsigned int nslots, stride, index, wrap, min_align_mask, page_offset;
 	int i;
 	unsigned long mask;
 	unsigned long offset_slots;
@@ -500,12 +500,16 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev, phys_addr_t orig_addr,
 		    ? ALIGN(mask + 1, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT
 		    : 1UL << (BITS_PER_LONG - IO_TLB_SHIFT);
 
+	min_align_mask = dma_get_min_align_mask(hwdev);
+	page_offset = orig_addr & min_align_mask;
+	alloc_size += page_offset;
+
 	/*
 	 * For mappings greater than or equal to a page, we limit the stride
 	 * (and hence alignment) to a page size.
 	 */
 	nslots = ALIGN(alloc_size, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;
-	if (alloc_size >= PAGE_SIZE)
+	if ((alloc_size >= PAGE_SIZE) || (min_align_mask > (1 << IO_TLB_SHIFT)))
 		stride = (1 << (PAGE_SHIFT - IO_TLB_SHIFT));
 	else
 		stride = 1;
@@ -583,6 +587,11 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev, phys_addr_t orig_addr,
 	 */
 	for (i = 0; i < nslots; i++)
 		io_tlb_orig_addr[index+i] = orig_addr + (i << IO_TLB_SHIFT);
+	/*
+	 * When keeping the offset of the original data, we need to advance
+	 * the tlb_addr by the offset of orig_addr.
+	 */
+	tlb_addr += page_offset;
 	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) &&
 	    (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL))
 		swiotlb_bounce(orig_addr, tlb_addr, mapping_size, DMA_TO_DEVICE);
@@ -598,7 +607,11 @@ void swiotlb_tbl_unmap_single(struct device *hwdev, phys_addr_t tlb_addr,
 			      enum dma_data_direction dir, unsigned long attrs)
 {
 	unsigned long flags;
-	int i, count, nslots = ALIGN(alloc_size, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;
+	unsigned int num_page_offset_slabs;
+	unsigned int min_align_mask = dma_get_min_align_mask(hwdev);
+	int i, count;
+	int nslots = ALIGN(alloc_size + (tlb_addr & min_align_mask),
+			1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;
 	int index = (tlb_addr - io_tlb_start) >> IO_TLB_SHIFT;
 	phys_addr_t orig_addr = io_tlb_orig_addr[index];
 
@@ -610,6 +623,14 @@ void swiotlb_tbl_unmap_single(struct device *hwdev, phys_addr_t tlb_addr,
 	    ((dir == DMA_FROM_DEVICE) || (dir == DMA_BIDIRECTIONAL)))
 		swiotlb_bounce(orig_addr, tlb_addr, mapping_size, DMA_FROM_DEVICE);
 
+	/*
+	 * When dma_get_min_align_mask is used, we may have padded more slabs
+	 * when padding exceeds one slab. We need to move index back to the
+	 * beginning of the padding.
+	 */
+	num_page_offset_slabs = (tlb_addr & min_align_mask) / (1 << IO_TLB_SHIFT);
+	index -= num_page_offset_slabs;
+
 	/*
 	 * Return the buffer to the free list by setting the corresponding
 	 * entries to indicate the number of contiguous entries available.
-- 
2.27.0