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[Xen-devel] Re: [PATCH] x86: define arch_vm_get_page_prot to set _PAGE_I

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] Re: [PATCH] x86: define arch_vm_get_page_prot to set _PAGE_IOMAP on VM_IO vmas
From: "H. Peter Anvin" <hpa@xxxxxxxxx>
Date: Thu, 21 Oct 2010 17:45:44 -0700
Cc: "Xen-devel@xxxxxxxxxxxxxxxxxxx" <Xen-devel@xxxxxxxxxxxxxxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
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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...


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

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