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

To: Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, "Petersson, Mats" <Mats.Petersson@xxxxxxx>
Subject: Re: [Xen-devel] A different probklem with save/restore on C/S 14823.
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Fri, 13 Apr 2007 17:43:15 +0100
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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.

 -- Keir

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