linux-kernel - New x886-Setup code breaks HVM-XEN boot

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Date:	Thu, 30 Aug 2007 16:15:28 +0200
From:	Christian Ehrhardt <lk@...e.de>
To:	linux-kernel@...r.kernel.org, hpa@...or.com
Subject: New x886-Setup code breaks HVM-XEN boot

Hi,

I am trying to boot a current 2.6 kernel as a guest under XEN in HVM mode.
With linux-2.6.22.(5) as the guest this works fine but current git kernels
fail very early in the boot process.

The XEN host is a debian kernel with XEN enabled (2.6.18-4-xen-686).
The XEN guest is a vanilla kernel from kernel org booting with LILO
22.6.1 in HVM mode.

I bisected the problem and the bisection points at this commit:
| # bad: [4fd06960f120e02e9abc802a09f9511c400042a5] Use the new x86 setup code for i386
| git-bisect bad 4fd06960f120e02e9abc802a09f9511c400042a5

The boot of a current git snapshot fails as follows:
bash$ sudo xm console guest
LILO 22.6.1 boot: lkcur
Loading lkcur.........................
BIOS data check bypassed
bash$

Note the the xm console command terminates on its own, i.e. the guest
machine seems to halt and not hang somewhere.

I could verify that the real mode code up to the assembly code in
pmjump.S is in fact executed. The problem appears to occur while
enabling protected mode. I tried to put endless loops into the 32-bit
setup code but these were apparently not reached. As far as I understand
this, the protected mode jump in pmjump.S seems to jump into nowhere.

I am willing to do tests with the XEN guest and send any additional
information that might be helpful. However, I cannot change the XEN host
at this time.

Any suggestions? 

     regards  Christian
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