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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: Fri, 13 Apr 2007 18:47:02 +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: 13 April 2007 17:43
> To: Tim Deegan; Petersson, Mats
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] A different probklem with 
> save/restore on C/S 14823.
> On 13/4/07 17:35, "Tim Deegan" <Tim.Deegan@xxxxxxxxxxxxx> wrote:
> > At 18:24 +0200 on 13 Apr (1176488676), Petersson, Mats wrote:
> >> I'm not seeing the problem that Fan Zhao is reporting, 
> instead I get
> >> this one. Not sure if ti's the same one or a different 
> problem... This
> >> happens with my simple-guest [i.e. not using hvmloader, as 
> I described
> >> before]. This worked fine yesterday.
> > 
> > This looks like the same problem (but caught in Xen instead of
> > crashing).  The restore path isn't setting the ioreq page's PFN
> > properly.   Have you reinstalled your tools (in particular 
> libxenguest)
> > since cset 14830:e3b3800c769a ?
> It is also somewhat odd that Xen got a chance to catch the 
> problem (probably
> the printed guest EIP is an I/O port operation? In which case 
> Xen caught the
> problem in send_pio_req), rather than crashing in 
> hvm_do_resume() with a
> NULL pointer dereference, which is what Fan Zhao saw. Either the guest
> started executing without passing through hvm_do_resume(), or 
> there was a
> valid page mapping at address 0 in Xen's address space when 
> you executed
> hvm_do_resume(). Neither of these possibilities is good. It 
> might be worth
> doing a bit of digging to find out why you didn't repro the 
> exact same crash
> as Fan Zhao.

See my other reply, although you may have a point about mapping - my
guest is running with the HVMloaders map, which probably maps all memory
available to guest linearly, including address zero (as that's where
real-mode puts the interrupt vector table, which can be useful to have
mapped - just a little bit ;-) ). 

So maybe we need an earlier/different test to kill guest? Or do you
think this is such a critical error that hypervisor should die?

>  -- Keir

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