Re: [PATCH] [PATCH] Adding offset keeping option when mapping data via SWIOTLB.

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Mon, Nov 23, 2020 at 02:18:07PM -0800, Jianxiong Gao wrote:
> NVMe driver and other applications may 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.

RHEL? So a specific RHEL kernel. Is there a Red Hat bug created
for this that can be linked to this patch to make it easier
for folks to figure this?

Why would you be using swiotlb=force?
Ah, you are using AMD SEV!

> This patch adds an option to make sure the mapped data preserves
> its offset of the orginal addrss. Tested on latest kernel that

s/addrss/address/
> this patch fixes the issue.
> 
> Signed-off-by: Jianxiong Gao <jxgao@google.com>
> Acked-by: David Rientjes <rientjes@google.com>
> ---
>  drivers/nvme/host/pci.c     |  3 ++-
>  include/linux/dma-mapping.h |  8 ++++++++
>  kernel/dma/swiotlb.c        | 13 +++++++++++++
>  3 files changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 0578ff253c47..a366fb8a1ff0 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -833,7 +833,8 @@ static blk_status_t nvme_map_data(struct nvme_dev *dev, struct request *req,
>  				iod->nents, rq_dma_dir(req), DMA_ATTR_NO_WARN);
>  	else
>  		nr_mapped = dma_map_sg_attrs(dev->dev, iod->sg, iod->nents,
> -					     rq_dma_dir(req), DMA_ATTR_NO_WARN);
> +				rq_dma_dir(req),
> +			       	DMA_ATTR_NO_WARN|DMA_ATTR_SWIOTLB_KEEP_OFFSET);
>  	if (!nr_mapped)
>  		goto out;
>  
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index 956151052d45..e46d23d9fa20 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -61,6 +61,14 @@
>   */
>  #define DMA_ATTR_PRIVILEGED		(1UL << 9)
>  
> +/*
> + * DMA_ATTR_SWIOTLB_KEEP_OFFSET: used to indicate that the buffer has to keep
> + * its offset when mapped via SWIOTLB. Some application functionality depends
> + * on the address offset, thus when buffers are mapped via SWIOTLB, the offset
> + * needs to be preserved.
> + */
> +#define DMA_ATTR_SWIOTLB_KEEP_OFFSET	(1UL << 10)
> +
>  /*
>   * A dma_addr_t can hold any valid DMA or bus address for the platform.  It can
>   * be given to a device to use as a DMA source or target.  It is specific to a
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 781b9dca197c..f43d7be1342d 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -483,6 +483,13 @@ 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);
> + 
> +	/*
> +	 * If we need to keep the offset when mapping, we need to add the offset
> +	 * to the total set we need to allocate in SWIOTLB
> +	 */
> +	if (attrs & DMA_ATTR_SWIOTLB_KEEP_OFFSET)
> +		alloc_size += offset_in_page(orig_addr);
>  
>  	/*
>  	 * For mappings greater than or equal to a page, we limit the stride
> @@ -567,6 +574,12 @@ 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.
> +	 */
> +	if (attrs & DMA_ATTR_SWIOTLB_KEEP_OFFSET)
> +		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
> 
>