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Re: [Xen-devel] Re: [PATCH] switch to a known good/static GDT beforekexe

To: Jan Beulich <JBeulich@xxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH] switch to a known good/static GDT beforekexec
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Thu, 02 Jul 2009 13:38:08 +0100
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Thread-topic: [Xen-devel] Re: [PATCH] switch to a known good/static GDT beforekexec
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On 02/07/2009 12:45, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:

>>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 02.07.09 13:11 >>>
>> I have one more question then -- when need_full_gdt(n), why do we always
>> unconditionally rewrite the l1es mapping the reserved gdt entries? Shouldn't
>> that be done on vcpu creation only and perhaps on compat mode switch (i.e.,
>> isn't it wasteful to do it in the context switch path)?
> While that's correct, we're talking about a single memory write here (plus
> the setup code), which I think is no more wasteful than adding the extra
> checking that would be needed to see whether we switch between
> compat and !compat (including the !need_full_gdt(p) case, where we
> don't know what kind of mapping we currently have).

Hm yes, fair enough.

 -- Keir

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