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Re: Guest-visible phys2mach part of Xen arch-neutral API? was: [Xen-deve

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Subject: Re: Guest-visible phys2mach part of Xen arch-neutral API? was: [Xen-devel] Uses of &frame_table[xfn]
From: Hollis Blanchard <hollisb@xxxxxxxxxx>
Date: Tue, 3 Jan 2006 15:55:20 -0600
Cc: Jimi Xenidis <jimix@xxxxxxxxxxxxxx>
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On Friday 30 December 2005 13:50, Magenheimer, Dan (HP Labs Fort Collins) 
> I think there are two critical questions that are very highly
> related.  To me, the critical question is how many changes
> to a guest are required to run on Xen.  I've argued for a long
> time that paravirtualization changes should be minimized/optimized
> to only those that are absolutely necessary for functionality
> and performance.   DMA-capable domains require either p==m
> or non-trivial changes to the guest.  On x86, non-trivial changes
> to the guest are necessary anyway due to the x86 memory architecture
> so p!=m comes "for free".  This is not necessarily the case
> for non-x86 Xen machines.

For the record, the PowerPC port is not currently using a p2m table in dom0 
(or any domain for that matter). We are still using the PAPR interface (IBM's 
enterprise hypervisor ABI) for memory management.

Using Xen terminology, that interface says that domains pass only physical 
addresses to the hypervisor, and the hypervisor performs the physical to 
machine translation.

I think we're not looking to diverge from this interface unless we absolutely 
have to, and so far (given the maturity of the PPC port) we haven't had to.

Hollis Blanchard
IBM Linux Technology Center

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