From mboxrd@z Thu Jan  1 00:00:00 1970
From: Zachary Amsden <zach@vmware.com>
Subject: Re: proposed interface change for setting the ldt
Date: Sun, 20 Aug 2006 22:01:49 -0700
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To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Chris Wright <chrisw@sous-sol.org>, Virtualization Mailing List <virtualization@lists.osdl.org>
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Jeremy Fitzhardinge wrote:
> Rusty Russell wrote:
>> It sounds fine to me, although I'd like to see the patch.  I don't have
>> anything against higher-level abstractions, if it helps any hypervisor,
>> as long as it doesn't warp the kernel code.  And if most hypervisors and
>> native break it down the same way, well, we can always create helpers.
>>   =

>
> Doing it this way does save a lot of complexity in the Xen case, which =

> would otherwise have to:
>
>   1. unpack the descriptor
>   2. if it's an LDT, save it off in a per-cpu structure
>   3. when load_ldt_desc is called, look up the structure, extract the
>      base+size of the ldt, and make a hypercall to set the ldt
>
> vs
>
>   1. set the ldt

This way works for us as well, but my opinion is - Xen deliberately =

broke the x86 interface here, for no strong reason.  In an ideal world, =

we shouldn't have to change Linux to work around that, nor should other =

hypervisors have to live with the consequences of that decision.  So I =

believe the onus is on Xen to fix the problem in their layer, not the =

other way around.  But I have no problem adapting to this way of doing =

things for now, since this is not performance critical, and LDT is =

barely used in Linux anyway, even then, mostly by unsupported =

applications in a paravirtualized world.

Zach