WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

RE: [Xen-devel] [PATCH] fix for Failed VMEntry on VMX

To: "David Lively" <dlively@xxxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-devel] [PATCH] fix for Failed VMEntry on VMX
From: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
Date: Tue, 2 May 2006 17:30:31 +0200
Delivery-date: Tue, 02 May 2006 08:30:57 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AcZt+c5zjV6erVBoTKm82WGNYtPpZQAAwEFQ
Thread-topic: [Xen-devel] [PATCH] fix for Failed VMEntry on VMX
 

> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> David Lively
> Sent: 02 May 2006 15:58
> To: xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-devel] [PATCH] fix for Failed VMEntry on VMX
> 
> I've been getting a "Failed VMEntry" when trying to boot a 
> second VMX guest (while the first one is still running, but 
> is no longer in real mode).  This patch fixes it.
> 
> VMX(assist) uses vm86 in its real mode emulation.  Upon 
> vmentry into a guest in vm86 mode, all segment bases must be 
> equal to the corresponding segment selector shifted left four 
> bits.  The vmx routine vmx_load_cpu_guest_regs() was loading 
> the segment selectors.  Now it makes sure to set the segment 
> bases appropriately if we're in vm86 mode.
> 
> Tested on 64bit hypervisor with 2 64-bit VMX domUs (on 2-way dom0).

Will this not break "big real-mode" type behaviour? Or am I missing
something here? Certainly the x86 architecture itself allows the segment
(in real mode) to have a different base address than the "selector << 4"
that you get when you LOAD a selector in REAL MODE. It's just that in
real-mode, you can't set a different base, but code that has temporarily
run in non-real mode (i.e. enter protected mode then set segment
register than exit back to real-mode) can do all sorts of magic. If this
is really expected behaviour, it would also be expected to have a limit
of 0xffff, or you're sort of half-breaking the rules still... 

--
Mats
> 
> Dave
> 


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel