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Re: [Xen-devel] question about patch 13252

To: "Lu, Guanqun" <guanqun.lu@xxxxxxxxx>, "jbeulich@xxxxxxxxxx" <jbeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] question about patch 13252
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Thu, 19 Mar 2009 14:22:39 +0000
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On 19/03/2009 14:07, "Lu, Guanqun" <guanqun.lu@xxxxxxxxx> wrote:

> I have such question about the number 11, 11 is 1010 in binary format,

Try again. :D

> which means that the busy flat is set.  Then later, load_TR() is called.
> load_TR() is a wrapper around instruction 'ltr'.  As I consult SDM2A,
> it says that ltr will generate #GP, when the busy flag is set.
> So I'm a little puzzled. Can you explain a little why it's not 9 ?
> Or am I missing something here?

We only execute LTR once at start of day for each CPU. This is done while
running on the non-compat gdt_table. When we switch to compat_gdt_table we
do not do any LTR switch. I suppose Jan sets the busy bit to match what will
be in the non-compat table after we have executed our one-off LTR.

 -- Keir

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