linux-kernel - Re: [PATCH] x86: define arch_vm_get_page_prot to set _PAGE_IOMAP on VM

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Date:	Thu, 21 Oct 2010 15:47:52 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	the arch/x86 maintainers <x86@...nel.org>,
	"Xen-devel@...ts.xensource.com" <Xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH] x86: define arch_vm_get_page_prot to set _PAGE_IOMAP
 on VM_IO vmas

On 10/21/2010 03:40 PM, Jeremy Fitzhardinge wrote:
> 
> Set _PAGE_IOMAP in ptes mapping a VM_IO vma.  This says that the mapping
> is of a real piece of physical hardware, and not just system memory.
> 
> Xen, in particular, uses to this to inhibit the normal pfn->mfn conversion
> that would normally happen - in other words, treat the address directly
> as a machine physical address without converting it from pseudo-physical.
> 
> [ Impact: make VM_IO mappings map the right thing under Xen ]
> 
> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> 

Am I the only one who thinks this seems extremely odd that the guest is
trusted to make this distinction?

	-hpa
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