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Re: [Xen-devel] xen 3.0 for AMD Pacifica

To: dfeustel@xxxxxxxxxxxxxx
Subject: Re: [Xen-devel] xen 3.0 for AMD Pacifica
From: Anthony Liguori <aliguori@xxxxxxxxxx>
Date: Tue, 25 Oct 2005 14:24:11 -0500
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Dave Feustel wrote:

On Tuesday 25 October 2005 09:53, Anthony Liguori wrote:
Dave Feustel wrote:

We intend to add support for x86 h/w virtualization extensions as information about them becomes available.
What information is needed beyond the Pacifica documentation already
provided by AMD and the Vanderpool docs provided by Intel?


I don't know where you're quoting from, but both specs are out publicly.

I know. I have both. What I was asking is whether the info in those documents
is sufficient to make Xen work with the hardware of both chips, or is additional info needed (and still not available)?

Sorry, then yes, theoritically, all you should need are those specs.

Both VT and Pacifica are pretty similiar in the basic idea that they allow the processor to be put in a mode where 30 or so events that normally don't trap actually do trap.

Pacifica has a new paging mode (paged real mode) made possible by the Opteron on-chip memory controller. This feature is not present in VT.
Yes, there are considerable differences. Pacifica has paged real mode whereas VT requires vm86 mode to be used for real mode emulation. Pacifica also has (optional) support for hardware shadow page tables, TLB tagging, and DMA memory protection. They also have different models for dealing with the VMCS/VMCB. I would categorize this stuff mostly as optimizations though since none of it's required to meet the Popek/Goldberg requirements.

Just enough differences to make things interesting :-)

Regards,

Anthony Liguori

Just having the processor trap though doesn't get you virtualization :-) Each of those events has to be handled, and often emulated. Throw in shadow paging and IO emulation and it's all rather complicated.

Plus, there's not much that can be done without having the hardware at this point.

Is there any possibility of setting up a mailing list directed specifically at
xen 3.0 hardware supported virtualization?


There are an awful lot of Xen mailing lists at this point. What would be *really* useful is having some content on the wiki that went into more depth about VT/Pacifica.

Regards,

Anthony Liguori

Thanks,
Dave Feustel




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