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

Konrad Rzeszutek Wilk
2021-01-28T17:21:56Z

On Wed, Jan 27, 2021 at 04:38:28PM -0800, Jianxiong Gao wrote:
> 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.

<scratches his head>

Didn't you send this patch like a month ago and someone pointed
out that the right fix would be in the NVMe driver?

Is there an issue with fixing the NVMe driver?

>
> 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
>