[PATCH] [PATCH] Keep offset when mapping data via SWIOTLB.

[Jianxiong Gao]

NVMe driver and other applications depend on the data offset
to operate correctly. Currently when unaligned data is mapped via
SWIOTLB, the data is mapped as slab aligned with the SWIOTLB. When
booting with --swiotlb=force option and using NVMe as interface,
running mkfs.xfs on Rhel fails because of the unalignment issue.
This patch makes sure the mapped data preserves
its offset of the orginal address. Tested on latest kernel that
this patch fixes the issue.

Signed-off-by: Jianxiong Gao <jxgao at google.com>
Acked-by: David Rientjes <rientjes at google.com>
---
 kernel/dma/swiotlb.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 781b9dca197c..56a35e71b3fd 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -483,6 +483,12 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev, phys_addr_t orig_addr,
 	max_slots = mask + 1
 		    ? ALIGN(mask + 1, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT
 		    : 1UL << (BITS_PER_LONG - IO_TLB_SHIFT);
+ 
+	/*
+	 * We need to keep the offset when mapping, so adding the offset
+	 * to the total set we need to allocate in SWIOTLB
+	 */
+	alloc_size += offset_in_page(orig_addr);
 
 	/*
 	 * For mappings greater than or equal to a page, we limit the stride
@@ -567,6 +573,11 @@ 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 += orig_addr & (PAGE_SIZE - 1);
 	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);
-- 
2.27.0