Re: [Xen-devel] Is there a way to add GDT entries without having

To:	Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject:	Re: [Xen-devel] Is there a way to add GDT entries without having a second page?
From:	Kip Macy <kip.macy@xxxxxxxxx>
Date:	Fri, 6 May 2005 08:31:19 -0700
Cc:	xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On 5/5/05, Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> wrote:
> 
> On 6 May 2005, at 01:50, Kip Macy wrote:
> 
> > I can add entries incrementally to the GDT by having a second page
> > frame lying around copying from the current one to the unused one and
> > then switching between them for updates, but is there a more elegant
> > way?
> 
> What's the problem? You want a 'writable GDT'? This is very doable
> since we have the emulator, but in Linux it was not hard to patch the
> places that write to the GDT to do a hypercall instead.

Each cpu in its initialization sequence adds additional entries to the
GDT. The pcpu data area is referenced through %fs, much like TLS. It
occurred to me after I had already asked the question that I could
just have the boot processor add the entries for all the CPUs so there
wouldn't be the need for any additional updates.

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