From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: is_xen_swiotlb_buffer() vs CONFIG_HIGHMEM
Date: Tue, 15 Dec 2009 10:34:01 -0800
Message-ID: <4B27D699.5080901@goop.org>
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To: Jan Beulich <JBeulich@novell.com>
Cc: xen-devel@lists.xensource.com, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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On 12/14/2009 07:02 AM, Jan Beulich wrote:
> shouldn't is_xen_swiotlb_buffer() also check against e.g. highstart_pfn
> to deal with wrap-around potentially leading to aliasing of
> [xen_io_tlb_start,xen_io_tlb_end)?
>    

So what you're saying is that if the pfn is for a high page, then 
"__va(pfn << PAGE_SHIFT);" is simply invalid.  The resulting addr is 
undefined, and may end up erroneously aliasing with the xen tlb buffer.

Do I understand your concern properly?

     J