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RE: [Xen-devel] [PATCH] VMXAssist: Bug fix (selector initialization)

  • To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "Guy Zana" <guy@xxxxxxxxxxxx>
  • Date: Sun, 20 May 2007 16:23:24 -0400
  • Delivery-date: Sun, 20 May 2007 13:25:27 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: Acea8NzqwaJQXijoT0OJdI8E07f9aAAF1ozoAARQuiA=
  • Thread-topic: [Xen-devel] [PATCH] VMXAssist: Bug fix (selector initialization)

> -----Original Message-----
> From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx] 
> Sent: Sunday, May 20, 2007 8:57 PM
> To: Guy Zana; xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] [PATCH] VMXAssist: Bug fix (selector 
> initialization)
> They are all set up this way because segment limits always 
> indicate the last accessible byte. Hence the limit is one 
> byte less than the size. You can see this clearly when 
> running a VMX guest: hit the 'v' debug key and look at the 
> contents of VMCS fields 0x4800-0x4812. You will see that all 
> these 32-bit limit fields contain odd numbers.

The limit should specify the number of bytes in the segment (Section 2.4.4 Vol 
(Which is exactly the sizeof of the struct :))
Maybe the VMCS are treated differently?

> The problem here is that the I/O bitmap should always be 
> terminated with an extra all-1s byte. See Section 13.5.2 of 
> Vol.1 the Intel PRM.

Missed that.


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