Re: [Xen-devel] [PATCH 03/11] xen/arm: simplify dma_cache_maint

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 27 Aug 2019, Christoph Hellwig wrote:
> And this was still buggy I think, it really needs some real Xen/Arm
> testing which I can't do.  Hopefully better version below:
> 
> --
> >From 5ad4b6e291dbb49f65480c9b769414931cbd485a Mon Sep 17 00:00:00 2001
> From: Christoph Hellwig <hch@xxxxxx>
> Date: Wed, 24 Jul 2019 15:26:08 +0200
> Subject: xen/arm: simplify dma_cache_maint
> 
> Calculate the required operation in the caller, and pass it directly
> instead of recalculating it for each page, and use simple arithmetics
> to get from the physical address to Xen page size aligned chunks.
> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
>  arch/arm/xen/mm.c | 61 ++++++++++++++++-------------------------------
>  1 file changed, 21 insertions(+), 40 deletions(-)
> 
> diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
> index 90574d89d0d4..2fde161733b0 100644
> --- a/arch/arm/xen/mm.c
> +++ b/arch/arm/xen/mm.c
> @@ -35,64 +35,45 @@ unsigned long xen_get_swiotlb_free_pages(unsigned int 
> order)
>       return __get_free_pages(flags, order);
>  }
>  
> -enum dma_cache_op {
> -       DMA_UNMAP,
> -       DMA_MAP,
> -};
>  static bool hypercall_cflush = false;
>  
> -/* functions called by SWIOTLB */
> -
> -static void dma_cache_maint(dma_addr_t handle, unsigned long offset,
> -     size_t size, enum dma_data_direction dir, enum dma_cache_op op)
> +/* buffers in highmem or foreign pages cannot cross page boundaries */
> +static void dma_cache_maint(dma_addr_t handle, size_t size, u32 op)
>  {
>       struct gnttab_cache_flush cflush;
> -     unsigned long xen_pfn;
> -     size_t left = size;
>  
> -     xen_pfn = (handle >> XEN_PAGE_SHIFT) + offset / XEN_PAGE_SIZE;
> -     offset %= XEN_PAGE_SIZE;
> +     cflush.a.dev_bus_addr = handle & XEN_PAGE_MASK;
> +     cflush.offset = xen_offset_in_page(handle);
> +     cflush.op = op;
>  
>       do {
> -             size_t len = left;
> -     
> -             /* buffers in highmem or foreign pages cannot cross page
> -              * boundaries */
> -             if (len + offset > XEN_PAGE_SIZE)
> -                     len = XEN_PAGE_SIZE - offset;
> -
> -             cflush.op = 0;
> -             cflush.a.dev_bus_addr = xen_pfn << XEN_PAGE_SHIFT;
> -             cflush.offset = offset;
> -             cflush.length = len;
> -
> -             if (op == DMA_UNMAP && dir != DMA_TO_DEVICE)
> -                     cflush.op = GNTTAB_CACHE_INVAL;
> -             if (op == DMA_MAP) {
> -                     if (dir == DMA_FROM_DEVICE)
> -                             cflush.op = GNTTAB_CACHE_INVAL;
> -                     else
> -                             cflush.op = GNTTAB_CACHE_CLEAN;
> -             }
> -             if (cflush.op)
> -                     HYPERVISOR_grant_table_op(GNTTABOP_cache_flush, 
> &cflush, 1);
> +             if (size + cflush.offset > XEN_PAGE_SIZE)
> +                     cflush.length = XEN_PAGE_SIZE - cflush.offset;
> +             else
> +                     cflush.length = size;
> +
> +             HYPERVISOR_grant_table_op(GNTTABOP_cache_flush, &cflush, 1);
>  
> -             offset = 0;
> -             xen_pfn++;
> -             left -= len;
> -     } while (left);
> +             cflush.offset = 0;
> +             cflush.a.dev_bus_addr += cflush.length;
> +             size -= cflush.length;

Yes that's better

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> +     } while (size);
>  }
>  
>  static void __xen_dma_page_dev_to_cpu(struct device *hwdev, dma_addr_t 
> handle,
>               size_t size, enum dma_data_direction dir)
>  {
> -     dma_cache_maint(handle & PAGE_MASK, handle & ~PAGE_MASK, size, dir, 
> DMA_UNMAP);
> +     if (dir != DMA_TO_DEVICE)
> +             dma_cache_maint(handle, size, GNTTAB_CACHE_INVAL);
>  }
>  
>  static void __xen_dma_page_cpu_to_dev(struct device *hwdev, dma_addr_t 
> handle,
>               size_t size, enum dma_data_direction dir)
>  {
> -     dma_cache_maint(handle & PAGE_MASK, handle & ~PAGE_MASK, size, dir, 
> DMA_MAP);
> +     if (dir == DMA_FROM_DEVICE)
> +             dma_cache_maint(handle, size, GNTTAB_CACHE_INVAL);
> +     else
> +             dma_cache_maint(handle, size, GNTTAB_CACHE_CLEAN);
>  }
>  
>  void __xen_dma_map_page(struct device *hwdev, struct page *page,
> -- 
> 2.20.1
> 

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