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Re: [Xen-devel] [PATCH, RFC] x86: make the GDT per-CPU

To: Jan Beulich <jbeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH, RFC] x86: make the GDT per-CPU
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Thu, 11 Sep 2008 14:15:51 +0100
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On 11/9/08 13:42, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

>> No, this would break 32-bits at least: The GDT entry for the selector
>> loaded into TR must remain a valid, busy TSS descriptor for the whole
>> lifetime of the system. So it can't be shared with the LDT. But even for
>> 64-bits I would fear using the same GDT slot for both LDT and GDT
>> loading.
> Actually, there's a second aspect here, too (again for 32-bits): As a
> follow-up patch I'm planning to make the double fault TSS per-CPU, too.
> This wasn't as simple with the global GDT as it would be with the per-CPU
> one.

Well, the extra LGDT looks like it will take about 130 cycles on Core-2
hardware. I suppose that is tolerable.

 -- Keir

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