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Re: [Xen-devel] Xen dom0 crash in get_phys_to_machine

To: Gianni Tedesco <gianni.tedesco@xxxxxxxxxx>
Subject: Re: [Xen-devel] Xen dom0 crash in get_phys_to_machine
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Fri, 22 Oct 2010 15:26:32 -0700
Cc: "Alan J. Wylie" <NDA5OWUy@xxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jeremy, Fitzhardinge <Jeremy.Fitzhardinge@xxxxxxxxxx>
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 On 10/22/2010 06:05 AM, Gianni Tedesco wrote:
> On Tue, 2010-10-12 at 08:55 +0100, Alan J. Wylie wrote:
>> Further to my previous report:
>> http://lists.xensource.com/archives/html/xen-devel/2010-10/msg00257.html
>> Message-ID: <19629.39326.337589.71778@xxxxxxxxxxx>
>> I've added some debugging and have tracked down the crash to the
>> recently modified code in arch/x86/xen/mmu.c
>> Since the last version of the code that worked for me, mmu.c has been
>> modified with a lot of P2M changes. It now crashes in
>> get_phys_to_machine().
>> Having tracked down the crash and the offending value of pfn, I then
>> further modified the code only to print if ( pfn == 0x18C3 ), and also
>> to print intermediate values.
>> <7>ALANW get_phys_to_machine pfn 000018C3
>> <7> topidx 00000000
>> <7> mididx 0000000C
>> <7> idx 000000C3
>> (XEN) d0:v0: unhandled page fault (ec=0000)
>> If there is any more debugging that I can do, I'll be only too happy to
>> oblige.
> FWIW, when I was checking for any call where pfn > max_pfn - and I got:
>   p2m_top[0][10][104] max_pfn=0
> The p2m seems to have been correctly initialised:
>  xen_build_dynamic_phys_to_machine: topidx=0 mididx=375 max_pfn=192512
> But then it looks like something is trampling max_pfn and possibly other
> important data structures.
> I can get a working pvops dom0 by reverting to commit
> e6b9b2cbca5093e8e38d3e314e2f6415ad951c60 - with the same config.
> git-bisect between that commit and head turned up some nonsense about a
> ata_piix change which just added a spinlock
> 876b3a81850fc237f643a065ea78ce2ad7665767 - so I assume that is a bisect
> problem and that this commit is unrelated...

Yeah.  If the problem appears as a function of kernel size, then
bisection is going to give you more or less random results, unfortunately.


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