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RE: [Xen-devel] A different probklem with save/restore on C/S 14823.

To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>, "Tim Deegan" <Tim.Deegan@xxxxxxxxxxxxx>
Subject: RE: [Xen-devel] A different probklem with save/restore on C/S 14823.
From: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
Date: Tue, 17 Apr 2007 16:26:21 +0200
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Thread-topic: [Xen-devel] A different probklem with save/restore on C/S 14823.

> -----Original Message-----
> From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx] 
> Sent: 17 April 2007 12:18
> To: Petersson, Mats; Tim Deegan
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] A different probklem with 
> save/restore on C/S 14823.
> On 17/4/07 09:54, "Petersson, Mats" <Mats.Petersson@xxxxxxx> wrote:
> >> populated? Dump the pagetable walk all the way down to the 
> mapping of
> >> address 0: what machine address is mapped there?
> > 
> > Whilst I agree this is a good path to go down, I'm not 
> quite sure why
> > cr3 would point anywhere but to monitor_table, is there any 
> (legal) case
> > where cr3 isn't this value when in the hypervisor?
> I don't think so. But equally, Xen should never create itself 
> a mapping at
> address zero. So it's worth dumping some obvious things and 
> sanity checking
> them.

Here's some debug output, hopefully sufficiently self-explanatory:
(XEN) hvm.c:debug_stuff:125: cr3=00000000559cf000,
(XEN) Pagetable walk from 0000000000000000:
(XEN)  L4[0x000] = 00000000559ce063 000000000001069c
(XEN)  L3[0x000] = 00000000559cd063 000000000001069b
(XEN)  L2[0x000] = 0000000000000000 ffffffffffffffff
(XEN) bad shared page: 0
(XEN) Trying to write to NULL!
(XEN) domain_crash_sync called from hvm.c:154
(XEN) Domain 2 (vcpu#0) crashed on cpu#1:
(XEN) ----[ Xen-3.0-unstable  x86_64  debug=n  Tainted:    C ]----
(XEN) CPU:    1
(XEN) RIP:    0010:[<00000000001022b1>]
(XEN) RFLAGS: 0000000000000297   CONTEXT: hvm
(XEN) rax: 0000000000001a18   rbx: 0000000000000000   rcx:
(XEN) rdx: 0000000000000050   rsi: 0000000000001e13   rdi:
(XEN) rbp: 00000000001058a8   rsp: 0000000000105880   r8:
(XEN) r9:  0000000000000000   r10: 0000000000000000   r11:
(XEN) r12: 0000000000000000   r13: 0000000000000000   r14:
(XEN) r15: 0000000000000000   cr0: 0000000000050033   cr4:
(XEN) cr3: 0000000000000000   cr2: 0000000000000000
(XEN) ds: 0008   es: 0008   fs: 0008   gs: 0008   ss: 0008   cs: 0010
(XEN) event_channel.c:178:d0 EVTCHNOP failure: domain 0, error -22, line

[The RIP of the guest indicates that it's at a HLT - which is very much
the expected place to be]. 

arch.monitor_table looks VERY different from CR3, but maybe I've done
something wrong when transforming from virtual to physical address, or
some such?

>  -- Keir

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