linux-kernel - Re: [PATCH v8 08/13] xen/arm: use hypercall to flush caches in map

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Message-ID: <20141110182659.GE25609@e104818-lin.cambridge.arm.com>
Date:	Mon, 10 Nov 2014 18:27:00 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"Ian.Campbell@...rix.com" <Ian.Campbell@...rix.com>,
	"david.vrabel@...rix.com" <david.vrabel@...rix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v8 08/13] xen/arm: use hypercall to flush caches in
 map_page

On Mon, Nov 10, 2014 at 04:14:00PM +0000, Stefano Stabellini wrote:
> In xen_dma_map_page, if the page is a local page, call the native
> map_page dma_ops. If the page is foreign, call __xen_dma_map_page that
> issues any required cache maintenane operations via hypercall.
> 
> The reason for doing this is that the native dma_ops map_page could
> allocate buffers than need to be freed. If the page is foreign we don't
> call the native unmap_page dma_ops function, resulting in a memory leak.
> 
> Suggested-by: Catalin Marinas <catalin.marinas@....com>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> ---
>  arch/arm/include/asm/xen/page-coherent.h |    9 ++++++++-
>  arch/arm/xen/mm32.c                      |   12 ++++++++++++
>  2 files changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/include/asm/xen/page-coherent.h b/arch/arm/include/asm/xen/page-coherent.h
> index 25d450c..36b79a8 100644
> --- a/arch/arm/include/asm/xen/page-coherent.h
> +++ b/arch/arm/include/asm/xen/page-coherent.h
> @@ -5,6 +5,9 @@
>  #include <linux/dma-attrs.h>
>  #include <linux/dma-mapping.h>
>  
> +void __xen_dma_map_page(struct device *hwdev, struct page *page,
> +	     dma_addr_t dev_addr, unsigned long offset, size_t size,
> +	     enum dma_data_direction dir, struct dma_attrs *attrs);
>  void __xen_dma_unmap_page(struct device *hwdev, dma_addr_t handle,
>  		size_t size, enum dma_data_direction dir,
>  		struct dma_attrs *attrs);
> @@ -32,7 +35,11 @@ static inline void xen_dma_map_page(struct device *hwdev, struct page *page,
>  	     dma_addr_t dev_addr, unsigned long offset, size_t size,
>  	     enum dma_data_direction dir, struct dma_attrs *attrs)
>  {
> -	__generic_dma_ops(hwdev)->map_page(hwdev, page, offset, size, dir, attrs);
> +	if (PFN_DOWN(dev_addr) == page_to_pfn(page)) {

Nitpick: you could write:

	bool foreign = PFN_DOWN(dev_addr) == page_to_pfn(page);

or even a static inline xen_foreign_page(page, dev_addr) function for
clarity. This code lacks comments.

> +		if (__generic_dma_ops(hwdev)->map_page)

I'm not sure we need to check map_page() here. I thought it's always
present as host DMA API does not check for it.

-- 
Catalin
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