linux-kernel - Re: [Xen-devel] [PATCH] xen/swiotlb: Exchange to contiguous memory for map

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Message-Id: <50C0ADB502000078000AE9DA@nat28.tlf.novell.com>
Date:	Thu, 06 Dec 2012 13:37:41 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Dongxiao Xu" <dongxiao.xu@...el.com>
Cc:	<xen-devel@...ts.xen.org>, <konrad.wilk@...cle.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH] xen/swiotlb: Exchange to contiguous
 memory for map_sg hook

>>> On 06.12.12 at 14:08, Dongxiao Xu <dongxiao.xu@...el.com> wrote:
> While mapping sg buffers, checking to cross page DMA buffer is
> also needed. If the guest DMA buffer crosses page boundary, Xen
> should exchange contiguous memory for it.
> 
> Besides, it is needed to backup the original page contents
> and copy it back after memory exchange is done.
> 
> This fixes issues if device DMA into software static buffers,
> and in case the static buffer cross page boundary which pages are
> not contiguous in real hardware.
> 
> Signed-off-by: Dongxiao Xu <dongxiao.xu@...el.com>
> Signed-off-by: Xiantao Zhang <xiantao.zhang@...el.com>
> ---
>  drivers/xen/swiotlb-xen.c |   47 
> ++++++++++++++++++++++++++++++++++++++++++++-
>  1 files changed, 46 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index 58db6df..e8f0cfb 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -461,6 +461,22 @@ xen_swiotlb_sync_single_for_device(struct device *hwdev, 
> dma_addr_t dev_addr,
>  }
>  EXPORT_SYMBOL_GPL(xen_swiotlb_sync_single_for_device);
>  
> +static bool
> +check_continguous_region(unsigned long vstart, unsigned long order)

check_continguous_region(unsigned long vstart, unsigned int order)

But - why do you need to do this check order based in the first
place? Checking the actual length of the buffer should suffice.

> +{
> +	unsigned long prev_ma = xen_virt_to_bus((void *)vstart);
> +	unsigned long next_ma;

phys_addr_t or some such for both of them.

> +	int i;

unsigned long

> +
> +	for (i = 1; i < (1 << order); i++) {

1UL

> +		next_ma = xen_virt_to_bus((void *)(vstart + i * PAGE_SIZE));
> +		if (next_ma != prev_ma + PAGE_SIZE)
> +			return false;
> +		prev_ma = next_ma;
> +	}
> +	return true;
> +}
> +
>  /*
>   * Map a set of buffers described by scatterlist in streaming mode for DMA.
>   * This is the scatter-gather version of the above xen_swiotlb_map_page
> @@ -489,7 +505,36 @@ xen_swiotlb_map_sg_attrs(struct device *hwdev, struct 
> scatterlist *sgl,
>  
>  	for_each_sg(sgl, sg, nelems, i) {
>  		phys_addr_t paddr = sg_phys(sg);
> -		dma_addr_t dev_addr = xen_phys_to_bus(paddr);
> +		unsigned long vstart, order;
> +		dma_addr_t dev_addr;
> +
> +		/*
> +		 * While mapping sg buffers, checking to cross page DMA buffer
> +		 * is also needed. If the guest DMA buffer crosses page
> +		 * boundary, Xen should exchange contiguous memory for it.
> +		 * Besides, it is needed to backup the original page contents
> +		 * and copy it back after memory exchange is done.
> +		 */
> +		if (range_straddles_page_boundary(paddr, sg->length)) {
> +			vstart = (unsigned long)__va(paddr & PAGE_MASK);
> +			order = get_order(sg->length + (paddr & ~PAGE_MASK));
> +			if (!check_continguous_region(vstart, order)) {
> +				unsigned long buf;
> +				buf = __get_free_pages(GFP_KERNEL, order);
> +				memcpy((void *)buf, (void *)vstart,
> +					PAGE_SIZE * (1 << order));
> +				if (xen_create_contiguous_region(vstart, order,
> +						fls64(paddr))) {
> +					free_pages(buf, order);
> +					return 0;
> +				}
> +				memcpy((void *)vstart, (void *)buf,
> +					PAGE_SIZE * (1 << order));
> +				free_pages(buf, order);
> +			}
> +		}
> +
> +		dev_addr = xen_phys_to_bus(paddr);
>  
>  		if (swiotlb_force ||
>  		    !dma_capable(hwdev, dev_addr, sg->length) ||

How about swiotlb_map_page() (for the compound page case)?

Jan

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