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Date:   Tue, 8 Dec 2020 17:16:17 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To:     Jianxiong Gao <jxgao@google.com>
Cc:     kbusch@kernel.org, axboe@fb.com, hch@lst.de, sagi@grimberg.me,
        m.szyprowski@samsung.com, robin.murphy@arm.com,
        linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org,
        iommu@lists.linux-foundation.org,
        David Rientjes <rientjes@google.com>
Subject: Re: [PATCH] [PATCH] Keep offset when mapping data via SWIOTLB.
Message-ID: <20201208221617.GA27569@char.us.oracle.com>
References: <20201207214204.1839028-1-jxgao@google.com>
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On Mon, Dec 07, 2020 at 01:42:04PM -0800, Jianxiong Gao wrote:
> 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.

Lets reword this comment a bit more since you are not providing
the RHEL Bug, and instead are focusing on the upstream kernel.

I can do that for you..

> 
> Signed-off-by: Jianxiong Gao <jxgao@google.com>
> Acked-by: David Rientjes <rientjes@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
> 
>