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