linux-kernel - Re: [PATCH v9 13/13] swiotlb-xen: remove BUG_ON in xen_bus_to

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Message-ID: <20141119210626.GD20440@laptop.dumpdata.com>
Date:	Wed, 19 Nov 2014 16:06:26 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	xen-devel@...ts.xensource.com, Ian.Campbell@...rix.com,
	david.vrabel@...rix.com, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, catalin.marinas@....com
Subject: Re: [PATCH v9 13/13] swiotlb-xen: remove BUG_ON in xen_bus_to_phys

On Wed, Nov 12, 2014 at 11:40:54AM +0000, Stefano Stabellini wrote:
> On x86 truncation cannot occur because config XEN depends on X86_64 ||
> (X86_32 && X86_PAE).
> 
> On ARM truncation can occur without CONFIG_ARM_LPAE, when the dma
> operation involves foreign grants. However in that case the physical
> address returned by xen_bus_to_phys is actually invalid (there is no mfn
> to pfn tracking for foreign grants on ARM) and it is not used.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@....com>

Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
>  drivers/xen/swiotlb-xen.c |    2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index 498b654..153cf14 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -96,8 +96,6 @@ static inline phys_addr_t xen_bus_to_phys(dma_addr_t baddr)
>  	dma_addr_t dma = (dma_addr_t)pfn << PAGE_SHIFT;
>  	phys_addr_t paddr = dma;
>  
> -	BUG_ON(paddr != dma); /* truncation has occurred, should never happen */
> -
>  	paddr |= baddr & ~PAGE_MASK;
>  
>  	return paddr;
> -- 
> 1.7.10.4
> 
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