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RE: [Xen-devel] more segment/selector handling woes


  • To: "Jan Beulich" <jbeulich@xxxxxxxxxx>
  • From: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
  • Date: Thu, 23 Nov 2006 14:06:06 +0100
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Thu, 23 Nov 2006 05:09:32 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AccOK4PhgMGP8O8XQbmEmVqFZD4hwAA1EvZg
  • Thread-topic: [Xen-devel] more segment/selector handling woes

> Note the wording 'as if' - this doesn't tell me whether the 
> internal base
> address field (which gets stored to the vmcb) can indeed be 
> relied upon.
> But obviously the code would be simpler if that was the case 
> in reality
> (and then perhaps the documentation could be updated accordingly).

Indeed, you're right: You need to check if the processor is in 64-bit
mode and if so, return base as zero, as the base value may not be zero
when the processor is storing it. This is so that 64-bit OS's can load a
32-bit segment before jumping to the actual code. 

I just got this confirmed by Ben Serebrin... 

--
Mats



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