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

Jianxiong Gao
2021-01-28T00:41:41Z

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@google.com>
---
kernel/dma/swiotlb.c | 25 ++++++++++++++++++++++---
1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 7c42df6e6100..4cab35f2c9bc 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, page_offset_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);

+ page_offset_mask = dma_get_page_offset_mask(hwdev);
+ page_offset = orig_addr & page_offset_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) || (page_offset_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 +607,9 @@ 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, page_offset_mask = dma_get_page_offset_mask(hwdev);
+ int i, count;
+ int nslots = ALIGN(alloc_size + tlb_addr & page_offset_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 +621,14 @@ 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_page_offset_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 & page_offset_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