How can I help?

How can I help?

[Chris Stromblad]

Hi there,

Just wanted to introduce myself to the list and also ask a few
questions. My name is Chris, currently living in the UK, nerd by day and
even more so at night.

Today I thought about playing with KVM for the first time, but without
much luck. Reading the archives I noticed someone else was experiencing
the same problem, it's the "exception 12" problem in qemu/kvm.

While I am an okay C-programmer, I've got little experience with
kernel-development but would be happy to learn or assist in anyway I
can.

I'm currently working on an Intel Core 2 CPU, with Archlinux as choice
of distribution. If there is anything I can do to help, please let me
know!

/ Chris

PS: Ops, almost forgot. Are there any solutions for the "exception 12"
problem, or something I can do?



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Re: How can I help?

[Avi Kivity]

Chris Stromblad wrote:
> Hi there,
>
> Just wanted to introduce myself to the list and also ask a few
> questions. My name is Chris, currently living in the UK, nerd by day and
> even more so at night.
>
> Today I thought about playing with KVM for the first time, but without
> much luck. Reading the archives I noticed someone else was experiencing
> the same problem, it's the "exception 12" problem in qemu/kvm.
>
> While I am an okay C-programmer, I've got little experience with
> kernel-development but would be happy to learn or assist in anyway I
> can.
>
>   

Unfortunately hacking on the code requires much poring over ancient 
manuscripts, a thorough understanding of the glorious history of the x86 
architecture, and much banging of heads against walls.  So unless you're 
prepared to spend quite a bit of time on kvm, your best bet is in testing.

Having a regression test of a real workload with timing measurements 
always helps, prefereably with multiple virtual machines running 
concurrently.


> I'm currently working on an Intel Core 2 CPU, with Archlinux as choice
> of distribution. If there is anything I can do to help, please let me
> know!
>
> / Chris
>
> PS: Ops, almost forgot. Are there any solutions for the "exception 12"
> problem, or something I can do?
>
>   

What guest are you running?  At what stage are you seeing the problem?  
Usually the workaround involves disabling the bootloader splashscreen or 
switching bootloaders.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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Re: How can I help?

[Chris Stromblad]

Few years ago I did a fair bit of x86 programming, but with the more
recent CPUs and all the new instructions, I'd probably be bit out of it.
Then again, wouldn't hurt having a look at it... who knows, maybe in a
few years I could actually do something ;)

The problem.

Basically I get the problem immediately when attempting to boot from an
ISO image (the installation step). The image is a UBUNTU x86_64
installation disk. Pretty much instantly when I attempt to boot the
window flashes by and in the original window I get the CPU reg dump with
the exception 12.

It works when using the unmodified version of QEMU.

/ Chris

On Sun, 2007-02-25 at 07:25 +0200, Avi Kivity wrote:
> Chris Stromblad wrote:
> > Hi there,
> >
> > Just wanted to introduce myself to the list and also ask a few
> > questions. My name is Chris, currently living in the UK, nerd by day and
> > even more so at night.
> >
> > Today I thought about playing with KVM for the first time, but without
> > much luck. Reading the archives I noticed someone else was experiencing
> > the same problem, it's the "exception 12" problem in qemu/kvm.
> >
> > While I am an okay C-programmer, I've got little experience with
> > kernel-development but would be happy to learn or assist in anyway I
> > can.
> >
> >   
> 
> Unfortunately hacking on the code requires much poring over ancient 
> manuscripts, a thorough understanding of the glorious history of the x86 
> architecture, and much banging of heads against walls.  So unless you're 
> prepared to spend quite a bit of time on kvm, your best bet is in testing.
> 
> Having a regression test of a real workload with timing measurements 
> always helps, prefereably with multiple virtual machines running 
> concurrently.
> 
> 
> > I'm currently working on an Intel Core 2 CPU, with Archlinux as choice
> > of distribution. If there is anything I can do to help, please let me
> > know!
> >
> > / Chris
> >
> > PS: Ops, almost forgot. Are there any solutions for the "exception 12"
> > problem, or something I can do?
> >
> >   
> 
> What guest are you running?  At what stage are you seeing the problem?  
> Usually the workaround involves disabling the bootloader splashscreen or 
> switching bootloaders.
> 



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Re: How can I help?

[Avi Kivity]

Chris Stromblad wrote:
> Few years ago I did a fair bit of x86 programming, but with the more
> recent CPUs and all the new instructions, I'd probably be bit out of it.
> Then again, wouldn't hurt having a look at it... who knows, maybe in a
> few years I could actually do something ;)
>
>   

x86 experience definitely helps.  You might want to download the latest 
Intel and AMD documentation and check out the relevant chapters.  For 
Intel, that's chapters 20-25 in the software developer's manual, volume 3B.

Actually knowing all the instructions isn't that important; it's the 
general quirkiness of the arch that needs to be understood.


> The problem.
>
> Basically I get the problem immediately when attempting to boot from an
> ISO image (the installation step). The image is a UBUNTU x86_64
> installation disk. Pretty much instantly when I attempt to boot the
> window flashes by and in the original window I get the CPU reg dump with
> the exception 12.
>   

Ok.  That's definitely the real-mode emulation problem we have on 
Intel.  You might try installing using qemu, and disabling any boot 
loader splashscreens (I don't know the exact syntax required), and 
restarting under kvm.

-- 
error compiling committee.c: too many arguments to function


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Re: How can I help?

[Chris Stromblad]

Sure, I'll have a look at the documentation. Need some evening reading
anyways ;)

Thanks for the suggestion I will try and install using QEMU and then
restart under KVM and the modified version of qemu, cheers!

/ Chris

On Sun, 2007-02-25 at 11:39 +0200, Avi Kivity wrote:
> Chris Stromblad wrote:
> > Few years ago I did a fair bit of x86 programming, but with the more
> > recent CPUs and all the new instructions, I'd probably be bit out of it.
> > Then again, wouldn't hurt having a look at it... who knows, maybe in a
> > few years I could actually do something ;)
> >
> >   
> 
> x86 experience definitely helps.  You might want to download the latest 
> Intel and AMD documentation and check out the relevant chapters.  For 
> Intel, that's chapters 20-25 in the software developer's manual, volume 3B.
> 
> Actually knowing all the instructions isn't that important; it's the 
> general quirkiness of the arch that needs to be understood.
> 
> 
> > The problem.
> >
> > Basically I get the problem immediately when attempting to boot from an
> > ISO image (the installation step). The image is a UBUNTU x86_64
> > installation disk. Pretty much instantly when I attempt to boot the
> > window flashes by and in the original window I get the CPU reg dump with
> > the exception 12.
> >   
> 
> Ok.  That's definitely the real-mode emulation problem we have on 
> Intel.  You might try installing using qemu, and disabling any boot 
> loader splashscreens (I don't know the exact syntax required), and 
> restarting under kvm.
> 



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Re: How can I help?

[Chris Stromblad]

Hi again,

Exactly how can I disable the bootsplash? And out of curiosity, why is
that preventing KVM/QEMU from working properly?

/ Chris

On Sun, 2007-02-25 at 11:39 +0200, Avi Kivity wrote:
> Chris Stromblad wrote:
> > Few years ago I did a fair bit of x86 programming, but with the more
> > recent CPUs and all the new instructions, I'd probably be bit out of it.
> > Then again, wouldn't hurt having a look at it... who knows, maybe in a
> > few years I could actually do something ;)
> >
> >   
> 
> x86 experience definitely helps.  You might want to download the latest 
> Intel and AMD documentation and check out the relevant chapters.  For 
> Intel, that's chapters 20-25 in the software developer's manual, volume 3B.
> 
> Actually knowing all the instructions isn't that important; it's the 
> general quirkiness of the arch that needs to be understood.
> 
> 
> > The problem.
> >
> > Basically I get the problem immediately when attempting to boot from an
> > ISO image (the installation step). The image is a UBUNTU x86_64
> > installation disk. Pretty much instantly when I attempt to boot the
> > window flashes by and in the original window I get the CPU reg dump with
> > the exception 12.
> >   
> 
> Ok.  That's definitely the real-mode emulation problem we have on 
> Intel.  You might try installing using qemu, and disabling any boot 
> loader splashscreens (I don't know the exact syntax required), and 
> restarting under kvm.
> 



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Re: How can I help?

[Avi Kivity]

Chris Stromblad wrote:
> Hi again,
>
> Exactly how can I disable the bootsplash? 

Install/boot with -no-kvm, then edit the grub configuration file.  The 
details vary, and I'm not sure how to do it on Ubuntu.


> And out of curiosity, why is
> that preventing KVM/QEMU from working properly?
>   

kvm uses vm86 mode to virtualize real mode.  Some boot loaders use 
features of real mode which are not present (or not identical to) vm86 mode.

One day we will emulate real mode (or use a combination of vm86 and 
emulation) which will fix the problem.

> / Chris
>
> On Sun, 2007-02-25 at 11:39 +0200, Avi Kivity wrote:
>   
>> Chris Stromblad wrote:
>>     
>>> Few years ago I did a fair bit of x86 programming, but with the more
>>> recent CPUs and all the new instructions, I'd probably be bit out of it.
>>> Then again, wouldn't hurt having a look at it... who knows, maybe in a
>>> few years I could actually do something ;)
>>>
>>>   
>>>       
>> x86 experience definitely helps.  You might want to download the latest 
>> Intel and AMD documentation and check out the relevant chapters.  For 
>> Intel, that's chapters 20-25 in the software developer's manual, volume 3B.
>>
>> Actually knowing all the instructions isn't that important; it's the 
>> general quirkiness of the arch that needs to be understood.
>>
>>
>>     
>>> The problem.
>>>
>>> Basically I get the problem immediately when attempting to boot from an
>>> ISO image (the installation step). The image is a UBUNTU x86_64
>>> installation disk. Pretty much instantly when I attempt to boot the
>>> window flashes by and in the original window I get the CPU reg dump with
>>> the exception 12.
>>>   
>>>       
>> Ok.  That's definitely the real-mode emulation problem we have on 
>> Intel.  You might try installing using qemu, and disabling any boot 
>> loader splashscreens (I don't know the exact syntax required), and 
>> restarting under kvm.
>>
>>     
>
>
>   


-- 
error compiling committee.c: too many arguments to function


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