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

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Message-ID: <4CC0DEB8.1060309@zytor.com>
Date:	Thu, 21 Oct 2010 17:45:44 -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 04:17 PM, Jeremy Fitzhardinge wrote:
> 
> Xen PV guests are always responsible for constructing ptes with machine
> addresses in them (ie, doing their own pseudo-physical to machine
> address conversion), and Xen verifies that the pages they want to map
> either belong to them or have been granted to them.  The _PAGE_IOMAP
> flag is a kernel-internal one which allows us to distinguish between
> ptes intended to map memory vs machine hardware addresses; it is not
> part of the Xen ABI.
> 
> If you're passing a device through to a domain, the domain is given
> access to the device's address space so it can legally map those pages
> (and if an IOMMU is available, the device is constrained to only DMA
> that domain's memory).
> 

Okay, could you clarify this part a bit?  Why does the kernel need to
know the difference between "pseudo-physical" and "machine addresses" at
all?  If they overlap, there is a problem, and if they don't overlap, it
will be a 1:1 mapping anyway...

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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