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Re: [Xen-devel] [RFC] Genapic in x86_64 Dom0

To: "Puthiyaparambil, Aravindh" <aravindh.puthiyaparambil@xxxxxxxxxx>
Subject: Re: [Xen-devel] [RFC] Genapic in x86_64 Dom0
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Sat, 20 Aug 2005 10:45:29 +0100
Cc: Chris Wright <chrisw@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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> I am working on a patch on to accommodate clustered APICs in x86_64
> Dom0/U Genapic. At the moment it defaults to flat. I am thinking of
> splitting genapic_xen into genapic_xen_flat and genapic_xen_cluster. 
> My question is that since the most of the code that checks for clustered
> vs flat has been IFDEFed out what is the best way to inform the Dom that
> it needs to run in clustered/flat APIC mode? Should I be thinking about
> introducing a new hypercall that does this or is there another standard
> way by which information is passed between Xen and Domains during boot
> that I can make use of?

Isn't flat/clustered mostly a local APIC issue? In which case domain 0
needn't care, as local APICs are entirely maintained by Xen.

As for IO APICs, although domain 0 writes the routing entries, Xen is
responsible for stamping in appropriate destination fields, based on
knowledge of physical CPU IDs and which domains are running on which
physical CPUs. This code can be extended to handle writing
clustering-compatible routing entries.

Perhaps genapic_xen is currently being too smart for its own good? :-)
On i386 we lobotomised local apic handling.

 -- Keir

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