linux-kernel - Re: New x86-Setup code breaks HVM-XEN boot

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Date:	Wed, 05 Sep 2007 14:06:05 +0100
From:	Ian Campbell <Ian.Campbell@...Source.com>
To:	Christian Ehrhardt <lk@...e.de>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-kernel@...r.kernel.org, hpa@...or.com
Subject: Re: New x86-Setup code breaks HVM-XEN boot

On Fri, 2007-08-31 at 09:54 +0200, Christian Ehrhardt wrote:
> (XEN) (GUEST: 353) Detected Xen v3.0.3-1 

I was unable to reproduce this problem on Xen 3.1.0 although I can't
immediately see a particular changeset which obviously fixed it. There
have been plenty of fixes to the emulator since 3.0.3 though so it's
worth trying a newer version.

In a later mail:
> The problem is with the lgdt instruction. Apparently XEN does not keep
> the contents of the 48-bit gdt_48 data structure that is passed to
> lgdt in the XEN machine state. Instead it appears to save the
> _address_ of the 48-bit descriptor somewhere. Unfortunately this data
> happens to reside on the stack and is probably no longer availiable at
> the time of the actual protected mode jump.

The emulation of lgdt (in tools/firmware/vmxassist/vm86.c) looks sane
enough on first glance (i.e. it saves the base and length not the
pointer) although it isn't an area of the code I'm particularly familiar
with.

Ian.

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