From: Andi Kleen <ak@suse.de>
To: Zachary Amsden <zach@vmware.com>
Subject: Re: [Xen-devel] Re: [RFC PATCH 18/35] Support gdt/idt/ldt handling =?utf-8?q?on=09Xen=2E?=
Date: Wed, 22 Mar 2006 18:36:23 +0100
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Cc: virtualization@lists.osdl.org, Chris Wright <chrisw@sous-sol.org>,
       Ian Pratt <ian.pratt@xensource.com>, xen-devel@lists.xensource.com,
       linux-kernel@vger.kernel.org
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On Wednesday 22 March 2006 18:51, Zachary Amsden wrote:

> 
> Yes, trapping works fine.  Even LLDT is infrequent. 

Not when you use old style LinuxThreads which use the LDT for TLS.

> No.  First, you have to create a special #GP handler for the general 
> protection fault.  

[... etc ...]

Sure but Xen already has the infrastructure for all of this and last
time I checked it was approaching and exceeding the size of the main
core kernel so a bit more of instruction emulation probably wouldn't 
do too much harm. 

In general I think any x86 hypervisor that attempts to work 
on current platforms needs instruction emulation because it is 
the only way to virtualize IO devices.

If this was supposed to be a interface for lots of hypervisors then maybe,
but so far it seems to only cover Xen and possibly some other bloatware 
ones.

That said I don't feel very strongly about emulating these instructions
or not as long as they can do that without too much code duplication.
The current patch are still a bit too excessive on the duplication front.

-Andi
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