linux-kernel - Re: 2.6.33-rc2: Xen/Guest switching to user mode with no user page tables

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Date:	Wed, 06 Jan 2010 14:38:29 +1100
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Christian Kujau <lists@...dbynature.de>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.33-rc2: Xen/Guest switching to user mode with no user page
 tables

On 01/06/2010 12:03 PM, Christian Kujau wrote:
> Hi there,
>
> a bit late with the testing again, I just found out that my Xen
> DomU won't boot with 2.6.33-rc2. The last working one is 2.6.32, I'll try
> to bisect if needed.
>
> The booting stops at:
>
> [    0.010000] no hardware sampling interrupt available.
> [    0.010000] Intel PMU driver.
> [    0.010000] ... version:                2
> [    0.010000] ... bit width:              40
> [    0.010000] ... generic registers:      2
> [    0.010000] ... value mask:             000000ffffffffff
> [    0.010000] ... max period:             000000007fffffff
> [    0.010000] ... fixed-purpose events:   3
> [    0.010000] ... event mask:             0000000700000003
> [    0.011314] Freeing SMP alternatives: 24k freed
>
>
> And "xm dmesg" says:
>
> xen# xm dmesg
> (XEN) traps.c:244:d88 Guest switching to user mode with no user page tables
> (XEN) traps.c:273:d88 Fatal error
>    

*Really* weird.  No idea how it could get into that state...  I've never 
seen this message before, even during development.  I'd suspect either a 
compiler bug, a miscompile, or some bad interaction with another patch.  
A bisection would be useful.

> (XEN) domain_crash called from traps.c:274
> (XEN) Domain 88 (vcpu#0) crashed on cpu#0:
> (XEN) ----[ Xen-3.2.1-rc1-pre  x86_64  debug=n  Not tainted ]----
> (XEN) CPU:    0
> (XEN) RIP:    e033:[<ffffffff810012eb>]
> (XEN) RFLAGS: 0000000000240246   CONTEXT: guest
> (XEN) rax: 0000000000000017   rbx: 0000000000000000   rcx: ffffffff810012eb
> (XEN) rdx: 0000000000000000   rsi: ffffffff810488a0   rdi: 0000000000000000
> (XEN) rbp: 0000000000000000   rsp: ffff88000f83df90   r8:  0000000000000000
> (XEN) r9:  0000000000000000   r10: 0000000000000000   r11: 0000000000240246
> (XEN) r12: 0000000000000000   r13: 0000000000000000   r14: 0000000000000000
> (XEN) r15: 0000000000000000   cr0: 000000008005003b   cr4: 00000000000026b0
> (XEN) cr3: 0000000096ba9000   cr2: 0000000000000000
> (XEN) ds: 0000   es: 0000   fs: 0000   gs: 0000   ss: e02b   cs: e033
> (XEN) Guest stack trace from rsp=ffff88000f83df90:
> (XEN)    0000000000000000 0000000000000202 ffffffff81009880 0000000000000100
> (XEN)    ffffffff81009880 0000000000000033 0000000000000202 0000000000000000
> (XEN)    000000000000002b ffffffff81009880 0000000000000011 0000000000000202
> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
>
> xen# gdb vmlinux.2010-01-05.6451
> (no debugging symbols found)
> (gdb) x/i 0xffffffff810012eb
> 0xffffffff810012eb<hypercall_page+747>:        add    %al,(%rax)
>
>
> The Dom0 is running a 2.6.24-24-xen Ubuntu kernel amd I'm kinda reluctant
> to upgrade, as I don't have a serial console to this MacMini, if things go
> wrong :-\
>
> I've put the .config (make oldconfig from 2.6.32) and dmesg on:
>
>    http://nerdbynature.de/bits/2.6.33-rc2/xen/
>    


     J
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