Xen users - May 2007 - xen over quemu OR quemu in Xen domU on a system with HVM-capable CPU

Hello all, 


I know that the question:

Is it possible to run quemu inside Xen domU
or run Xen domain 0 on quemu have discussed 
earlier in this mail list.

As far as I remember this is possible
except such a configuration where kquemu acceleration is in use.



But what about HVM-capable systems?


Please tell me are there the same restrictions for the hvm-capable systems?

Thank you!


-- 
WBR, i.m.chubin


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> -----Original Message-----
> From: xen-users-bounces@lists.xensource.com 
> [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of 
> Igor Chubin
> Sent: 30 May 2007 17:10
> To: xen-users@lists.xensource.com
> Subject: [Xen-users] xen over quemu OR quemu in Xen domU on a 
> system with HVM-capable CPU
> 
> 
> 
> Hello all, 
> 
> 
> I know that the question:
> 
> Is it possible to run quemu inside Xen domU
> or run Xen domain 0 on quemu have discussed 
> earlier in this mail list.
> 
> As far as I remember this is possible
> except such a configuration where kquemu acceleration is in use.
That is my understading too - kqemu needs to run in Ring 0, which is
reserved for the hypervisor under Xen. 
> 
> 
> 
> But what about HVM-capable systems?
> 
> 
> Please tell me are there the same restrictions for the 
> hvm-capable systems?
If you load Linux (or such) in HVM mode, you can run kqemu inside that
Linux. I''m not entirely sure I understand the advantage of this,
compared to running the OS you want to run in QEMU inside a HVM virtual
machine in the first place, but yes, it''s possible. 

--
Mats
> 
> Thank you!
> 
> 
> -- 
> WBR, i.m.chubin
> 
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
> 
> 
> 


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> Is it possible to run quemu inside Xen domU
Yes, but you won''t be able to use the kqemu accelerator module.
> or run Xen domain 0 on quemu have discussed
> earlier in this mail list.
I think that works too, I tested it out briefly and Xen booted inside kqemu.  
You won''t be able to use HVM-Xen inside Qemu even if your hardware
supports
it.
> But what about HVM-capable systems?
>
>
> Please tell me are there the same restrictions for the hvm-capable systems?
You can run probably qemu in an HVM guest.  You may even be able to run kqemu 
in an HVM guest.

If you use KVM you might be able to run non-HVM Xen as a guest inside that.

You can run non-HVM Xen inside HVM Xen (I do this regularly).

Does that cover all the cases you were interested in?

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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On Mi, Mai 30, 2007 at 07:09:55 +0300, Igor Chubin
wrote:
> 
> 
> Hello all, 
> 
> 
> I know that the question:
> 
> Is it possible to run quemu inside Xen domU
> or run Xen domain 0 on quemu have discussed 
> earlier in this mail list.
> 
> As far as I remember this is possible
> except such a configuration where kquemu acceleration is in use.
> 
> 
> 
> But what about HVM-capable systems?
> 
> 
> Please tell me are there the same restrictions for the hvm-capable systems?
> 



Actually, I want to run 

quemu + kquemu inside Xen Domain 0 on the HVM-capable system.

Is it possible?

> Thank you!
> 
> 
> -- 
> WBR, i.m.chubin
> 
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
-- 
WBR, i.m.chubin


_______________________________________________
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http://lists.xensource.com/xen-users

> -----Original Message-----
> From: xen-users-bounces@lists.xensource.com 
> [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of 
> Igor Chubin
> Sent: 30 May 2007 17:13
> To: Igor Chubin
> Cc: xen-users@lists.xensource.com
> Subject: Re: [Xen-users] xen over quemu OR quemu in Xen domU 
> on a system with HVM-capable CPU
> 
> On Mi, Mai 30, 2007 at 07:09:55 +0300, Igor Chubin wrote:
> > 
> > 
> > Hello all, 
> > 
> > 
> > I know that the question:
> > 
> > Is it possible to run quemu inside Xen domU
> > or run Xen domain 0 on quemu have discussed 
> > earlier in this mail list.
> > 
> > As far as I remember this is possible
> > except such a configuration where kquemu acceleration is in use.
> > 
> > 
> > 
> > But what about HVM-capable systems?
> > 
> > 
> > Please tell me are there the same restrictions for the 
> hvm-capable systems?
> > 
> 
> 
> 
> 
> Actually, I want to run 
> 
> quemu + kquemu inside Xen Domain 0 on the HVM-capable system.
No, because kqemu is still requiring access to ring 0 protection level
(that''s the highest privilege level), which is still not available to
anything other than the hypvervisor itself - you can get a "different"
ring 0 for guest domains, but that''s not in Dom0. 

So the answer to this question is the same as for non-HVM capable
systems. 

I still don''t quite understand what the purpose of running kqemu on top
of a HVM-capable system is, as it''s almost certain to be no faster than
running a HVM domain itself. It may not be FASTER to run the HVM domain
either - depending on what''s going on in the domain, but most cases it
probably is. 

--
Mats
> 
> Is it possible?
> 
> 
> > Thank you!
> > 
> > 
> > -- 
> > WBR, i.m.chubin
> > 
> > 
> > _______________________________________________
> > Xen-users mailing list
> > Xen-users@lists.xensource.com
> > http://lists.xensource.com/xen-users
> 
> -- 
> WBR, i.m.chubin
> 
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
> 
> 
> 


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...
> > But what about HVM-capable systems?
> > 
> > 
> > Please tell me are there the same restrictions for the 
> > hvm-capable systems?
> 
> If you load Linux (or such) in HVM mode, you can run kqemu inside that
> Linux. I''m not entirely sure I understand the advantage of this,
> compared to running the OS you want to run in QEMU inside a HVM virtual
> machine in the first place, but yes, it''s possible. 
> 

Mark and Mats,

Thank for your answers.

My current task is to run as many as possible different operating systems
in the same Xen domain 0 on the same machine (HVM-capable machine).

Better to run them inside domUs, but if this impossible
may be I could run qeumu+kquemu  processes inside dom0
(and operating system on them)?

+------++------++------++------++------++------+
|      ||Win   ||      ||      ||      ||      |
|Linux1||(HVM) ||Solaris| OS1  || OS2  || OS3  |
+------++------++------++------++------++------+
+------++------++------++------++------++------+
|      ||      ||      ||quemu+||qemu+ ||qemu+ |
| domU || domU || domU ||kquemu||kquemu||kquemu|
+------++------++------++------++------++------+
+----------------------------------------------+
|                                              |
|                Xen domain 0                  |
+----------------------------------------------+

As far as I know there are problems in running of some 
legacy operating systems in domU (HVM).


I have personally faced problem with (unmodified) FreeBSD 5 (and 6) 
running in the Xen HVM domU (this problem have discussed here; as
far as I remember the problem is related to real mode loader).

But I need not only FreeBSD but several other legacy operating
systems.

Of course, I''m not sure, that this systems will run in quemu, 
but I want to try.

> --
> Mats
> > 
> > Thank you!
> > 
> > 
> > -- 
> > WBR, i.m.chubin
> > 
> > 
> > _______________________________________________
> > Xen-users mailing list
> > Xen-users@lists.xensource.com
> > http://lists.xensource.com/xen-users
> > 
> > 
> > 
> 
-- 
WBR, i.m.chubin


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http://lists.xensource.com/xen-users

...
> > Please tell me are there the same restrictions for the 
> > hvm-capable systems?
> 
> If you load Linux (or such) in HVM mode, you can run kqemu inside that
> Linux. I''m not entirely sure I understand the advantage of this,
> compared to running the OS you want to run in QEMU inside a HVM virtual
> machine in the first place, but yes, it''s possible. 


Small addition.


Mats, I don''t want to run linux inside domU to run quemu.

I want to run quemu and kquemu in Xen domain 0 directly.

-- 
WBR, i.m.chubin


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> -----Original Message-----
> From: Igor Chubin [mailto:igor@chub.in] 
> Sent: 30 May 2007 17:34
> To: Petersson, Mats
> Cc: Igor Chubin; xen-users@lists.xensource.com
> Subject: Re: [Xen-users] xen over quemu OR quemu in Xen domU 
> on a system with HVM-capable CPU
> 
> ...
> > > Please tell me are there the same restrictions for the 
> > > hvm-capable systems?
> > 
> > If you load Linux (or such) in HVM mode, you can run kqemu 
> inside that
> > Linux. I''m not entirely sure I understand the advantage of
this,
> > compared to running the OS you want to run in QEMU inside a 
> HVM virtual
> > machine in the first place, but yes, it''s possible. 
> 
> 
> 
> Small addition.
> 
> 
> Mats, I don''t want to run linux inside domU to run quemu.
> 
> I want to run quemu and kquemu in Xen domain 0 directly.
Yes, but I still don''t understand why, including after your other
explanation about running "as many OS''s as possible", this is
better
than just running a HVM domain in the first place - HVM domains aren''t
VERY resource consuming, and you''ll be running a QEMU-DM or full-QEMU
per "guest"[1]. 

The only advantage I can see is that since QEMU itself is using virtual
memory, you could possibly swap a "guest" to disk, which means that
you
can overcommit the memory. I''m however sceptical that this is a REAL
advantage over running a virtual machine with swap in the guest - the
swapping within the guest would be much more selective on what gets
swapped out, compared to swapping out some "random" bits of the
"qemu+data" images. 

[1] Here I use the term guest in a looser meaning than I normally would
do, e.g. a QEMU instance would also count as a guest.  

--
Mats
> 
> -- 
> WBR, i.m.chubin
> 
> 
> 
> 


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Igor,

Just to clarify
> > Actually, I want to run
> >
> > quemu + kquemu inside Xen Domain 0 on the HVM-capable system.
What are you actually trying to achieve here?  It would probably help us 
understand what you wanted to do better if we knew why.

Cheers,
Mark
> No, because kqemu is still requiring access to ring 0 protection level
> (that''s the highest privilege level), which is still not available
to
> anything other than the hypvervisor itself - you can get a
"different"
> ring 0 for guest domains, but that''s not in Dom0.
>
> So the answer to this question is the same as for non-HVM capable
> systems.
>
> I still don''t quite understand what the purpose of running kqemu
on top
> of a HVM-capable system is, as it''s almost certain to be no faster
than
> running a HVM domain itself. It may not be FASTER to run the HVM domain
> either - depending on what''s going on in the domain, but most
cases it
> probably is.
>
> --
> Mats
>
> > Is it possible?
> >
> > > Thank you!
> > >
> > >
> > > --
> > > WBR, i.m.chubin
> > >
> > >
> > > _______________________________________________
> > > Xen-users mailing list
> > > Xen-users@lists.xensource.com
> > > http://lists.xensource.com/xen-users
> >
> > --
> > WBR, i.m.chubin
> >
> >
> > _______________________________________________
> > Xen-users mailing list
> > Xen-users@lists.xensource.com
> > http://lists.xensource.com/xen-users
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users


-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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On Mi, Mai 30, 2007 at 05:42:37 +0100, Mark Williamson
wrote:
> Igor,
> 
> Just to clarify
> 
> > > Actually, I want to run
> > >
> > > quemu + kquemu inside Xen Domain 0 on the HVM-capable system.
> 
> What are you actually trying to achieve here?  It would probably help us 
> understand what you wanted to do better if we knew why.

Thank you for your help.
And please, excuse me my bad English.

I''ll try to clarify what I want.

Example.

I can run FreeBSD inside quemu, but I can''t run FreeBSD 
(especially legacy FreeBSD, e.g. FreeBSD 5)
inside Xen domain.
Even on HVM capable machines.
(as far as I know proble is related to loader and big real mode).

As far as I can judge analogous problem exists for several other
systems. 

That is there are OS''es which we can run inside quemu but
can''t run
inside Xen domU.

Am I right?




Main operating system that I use is Linux.
And that is great how Linux runs inside Xen.
(As for me, Xen is the best here!)
Also there are many good mechanisms and tools to work with Xen infrastructure.

I like Xen networking, intelligent config files for domains, 
Xen live migration, XenAPI and many other Xen features.

So I want to find a way to run OSes (inside quemu or any other way)
that can not run directly in Xen domUs (even on HVM)
simultaneously with normal Xen domUs.



Thats my idea.

Hope that I have explained it better now.



May be, my information is out of date and today absolutely any
(x86,legacy) OS can run in Xen domU on an HVM capable machine?



-- 
WBR, i.m.chubin


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...
> > 
> > 
> > Actually, I want to run 
> > 
> > quemu + kquemu inside Xen Domain 0 on the HVM-capable system.
> 
> No, because kqemu is still requiring access to ring 0 protection level
> (that''s the highest privilege level), which is still not available
to
> anything other than the hypvervisor itself - you can get a
"different"
> ring 0 for guest domains, but that''s not in Dom0. 

So I can run kquemu inside domU but not in dom0?
Right?

I can get different ring 0 for domUs,
and this gives me possibilty to run kquemu inside domUs?
> 
> So the answer to this question is the same as for non-HVM capable
> systems. 
> 
> I still don''t quite understand what the purpose of running kqemu
on top
> of a HVM-capable system is, as it''s almost certain to be no faster
than
> running a HVM domain itself. It may not be FASTER to run the HVM domain
> either - depending on what''s going on in the domain, but most
cases it
> probably is. 
I have tried to explain what I want in the previous letter.


Mats, thank you for your help and for your answers.
Your letters really help me to understand Xen better.

-- 
WBR, i.m.chubin


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> Mats, I don''t want to run linux inside domU to run quemu.
>
> I want to run quemu and kquemu in Xen domain 0 directly.
That definitely won''t work, I''m afraid.  The only way
you''ll ever get kqemu
running is on a "native" system, or in an HVM guest (in the latter
case, I
don''t know how well it''d actually work).

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

_______________________________________________
Xen-users mailing list
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http://lists.xensource.com/xen-users

> Thank you for your help.
> And please, excuse me my bad English.
>
> I''ll try to clarify what I want.
>
> Example.
>
> I can run FreeBSD inside quemu, but I can''t run FreeBSD
> (especially legacy FreeBSD, e.g. FreeBSD 5)
> inside Xen domain.
> Even on HVM capable machines.
> (as far as I know proble is related to loader and big real mode).
Ah.  I have an AMD-V box that works with FreeBSD 6 OK...  Are you running on 
an Intel VT-x box?
> That is there are OS''es which we can run inside quemu but
can''t run
> inside Xen domU.
>
> Am I right?
Yes, if they mess with things like the big real mode stuff, which
aren''t fully
emulated at the moment...
> So I want to find a way to run OSes (inside quemu or any other way)
> that can not run directly in Xen domUs (even on HVM)
> simultaneously with normal Xen domUs.
> May be, my information is out of date and today absolutely any
> (x86,legacy) OS can run in Xen domU on an HVM capable machine?
Would the performance of plain Qemu be too slow for you?  That would be an 
easy first step to make...

You might find that the KVM virtualiser will support the OSes you want (or 
not :-/), but that''ll mean you can''t run Xen (except maybe as
a KVM guest).

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

On Wednesday 30 May 2007, Igor Chubin wrote:
> ...
>
> > > Actually, I want to run
> > >
> > > quemu + kquemu inside Xen Domain 0 on the HVM-capable system.
> >
> > No, because kqemu is still requiring access to ring 0 protection level
> > (that''s the highest privilege level), which is still not
available to
> > anything other than the hypvervisor itself - you can get a
"different"
> > ring 0 for guest domains, but that''s not in Dom0.
>
> So I can run kquemu inside domU but not in dom0?
> Right?
In a HVM domU, yes.  It should work in principle...
> I can get different ring 0 for domUs,
> and this gives me possibilty to run kquemu inside domUs?
Yes, but the performance might not be great, and I doubt anyone has ever 
tested that this works!

I guess the other thing to consider is whether you''d be better off
running
something like VMware server, if the freely available solutions don''t
fit
your needs?

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

_______________________________________________
Xen-users mailing list
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http://lists.xensource.com/xen-users

On Do, Mai 31, 2007 at 02:48:40 +0100, Mark Williamson
wrote:
> > Thank you for your help.
> > And please, excuse me my bad English.
> >
> > I''ll try to clarify what I want.
> >
> > Example.
> >
> > I can run FreeBSD inside quemu, but I can''t run FreeBSD
> > (especially legacy FreeBSD, e.g. FreeBSD 5)
> > inside Xen domain.
> > Even on HVM capable machines.
> > (as far as I know proble is related to loader and big real mode).
> 
> Ah.  I have an AMD-V box that works with FreeBSD 6 OK...  Are you running
on
> an Intel VT-x box?
> 
Yes.
At this moment I use Intel VT-x box for my experiments
(Hewlett-Packard DL380 G5 to be more precise).

But I can change my hardware if I''ll have good reasons for this.
The fact that FreeBSD runs in Xen domU''s on hosts with AMD CPUs, 
but not run on hosts with Intel CPUs is very serious, as for me.

(May it be that the main reason why FreeBSD runs on one system [AMD]
but does not want to run on another [Intel] is not CPU, but BIOS or
something else?)
> > That is there are OS''es which we can run inside quemu but
can''t run
> > inside Xen domU.
> >
> > Am I right?
> 
> Yes, if they mess with things like the big real mode stuff, which
aren''t fully
> emulated at the moment...
> 
> > So I want to find a way to run OSes (inside quemu or any other way)
> > that can not run directly in Xen domUs (even on HVM)
> > simultaneously with normal Xen domUs.
> 
> > May be, my information is out of date and today absolutely any
> > (x86,legacy) OS can run in Xen domU on an HVM capable machine?
> 
> Would the performance of plain Qemu be too slow for you?  That would be an 
> easy first step to make...
I think that this is the best variant.


As far as I understand I can run quemu VMs inside Xen domUs as well
as inside dom0.

> 
> You might find that the KVM virtualiser will support the OSes you want (or 
> not :-/), but that''ll mean you can''t run Xen (except
maybe as a KVM guest).
> 
Thank you for this advice, but I want to use Xen.
I like some of its features which KVM has not for the present.

I look for the additional solution, but not for the alternative.

-- 
WBR, i.m.chubin


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...
> > So I can run kquemu inside domU but not in dom0?
> > Right?
> 
> In a HVM domU, yes.  It should work in principle...
> 
> > I can get different ring 0 for domUs,
> > and this gives me possibilty to run kquemu inside domUs?
> 
> Yes, but the performance might not be great, and I doubt anyone has ever 
> tested that this works!
I hope I will test and will tell about my results.
> 
> I guess the other thing to consider is whether you''d be better off
running
> something like VMware server, if the freely available solutions
don''t fit
> your needs?
> 
No.

The scenario I''ve described (many OSes, Xen + quemu)
is for experimental purposes.
And my main goal in it is to get know more about Xen 
and its usage (especially in a heterogenous environment).

As for production environments,
we principally use Linux (and Windows with HVM in several cases)
and there are no problems with it.
> Cheers,
> Mark
> 
> -- 
> Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
> Mark: To answer a question with a question: What use is a skateboard?
> Dave: Skateboards have wheels.
> Mark: My wheel has a wheel!
-- 
WBR, i.m.chubin


_______________________________________________
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http://lists.xensource.com/xen-users

> -----Original Message-----
> From: Igor Chubin [mailto:igor@chub.in] 
> Sent: 31 May 2007 07:35
> To: Mark Williamson
> Cc: xen-users@lists.xensource.com; Igor Chubin; Petersson, Mats
> Subject: Re: [Xen-users] xen over quemu OR quemu in Xen domU 
> on a system with HVM-capable CPU
> 
> On Do, Mai 31, 2007 at 02:48:40 +0100, Mark Williamson wrote:
> > > Thank you for your help.
> > > And please, excuse me my bad English.
> > >
> > > I''ll try to clarify what I want.
> > >
> > > Example.
> > >
> > > I can run FreeBSD inside quemu, but I can''t run FreeBSD
> > > (especially legacy FreeBSD, e.g. FreeBSD 5)
> > > inside Xen domain.
> > > Even on HVM capable machines.
> > > (as far as I know proble is related to loader and big real mode).
> > 
> > Ah.  I have an AMD-V box that works with FreeBSD 6 OK...  
> Are you running on 
> > an Intel VT-x box?
> > 
> 
> Yes.
> At this moment I use Intel VT-x box for my experiments
> (Hewlett-Packard DL380 G5 to be more precise).
> 
> But I can change my hardware if I''ll have good reasons for this.
> The fact that FreeBSD runs in Xen domU''s on hosts with AMD CPUs, 
> but not run on hosts with Intel CPUs is very serious, as for me.
> 
> (May it be that the main reason why FreeBSD runs on one system [AMD]
> but does not want to run on another [Intel] is not CPU, but BIOS or
> something else?)
HVM domains do not use the BIOS in the machine they are running on at
all, so any BIOS difference should be completely ignored. 

In this particular case, I''m pretty sure the reason why it
doesn''t work
is that Intel''s VT doesn''t support real-mode guests. Instead,
they
emulate realmode in VM86 mode (so the processor is in protected 32-bit
mode, but running 16-bit real-mode style code). This works as long as
the instructions aren''t "ring 0" instructions - when these
instructions
are seen, they trap with a GP-fault. This is then handled in the
VMXassist code that emulates the relevant instruction. This is also
fine. The problem occurs when a transition is made from real mode to
protected mode and back again, where the registers (particular segment
registers) need to be preserved - you can''t do that in VM86 mode! So
registers set in protected mode are "reset" when re-entering
real-mode.
This makes "big real mode" tricks fail [big real mode is really just
going into protected mode, setting a segment to base=0, limit 0xFFFFFFFF, and
returning to real-mode - this allows real-mode code to
access all of the first 4GB of memory without any problems, rather than
being limited to 1MB]. Big real-mode is used by many boot-loaders. 

So as a conclusion, the difference here is the internal architecture of
the processor. AMD choose the "clever way", I think. 

--
Mats




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...
> > > Ah.  I have an AMD-V box that works with FreeBSD 6 OK...  
> > Are you running on 
> > > an Intel VT-x box?
> > > 
> > 
> > Yes.
> > At this moment I use Intel VT-x box for my experiments
> > (Hewlett-Packard DL380 G5 to be more precise).
> > 
> > But I can change my hardware if I''ll have good reasons for
this.
> > The fact that FreeBSD runs in Xen domU''s on hosts with AMD
CPUs,
> > but not run on hosts with Intel CPUs is very serious, as for me.
> > 
> > (May it be that the main reason why FreeBSD runs on one system [AMD]
> > but does not want to run on another [Intel] is not CPU, but BIOS or
> > something else?)
> 
> HVM domains do not use the BIOS in the machine they are running on at
> all, so any BIOS difference should be completely ignored. 
> 
> In this particular case, I''m pretty sure the reason why it
doesn''t work
> is that Intel''s VT doesn''t support real-mode guests.
Instead, they
> emulate realmode in VM86 mode (so the processor is in protected 32-bit
> mode, but running 16-bit real-mode style code). This works as long as
> the instructions aren''t "ring 0" instructions - when
these instructions
> are seen, they trap with a GP-fault. This is then handled in the
> VMXassist code that emulates the relevant instruction. This is also
> fine. The problem occurs when a transition is made from real mode to
> protected mode and back again, where the registers (particular segment
> registers) need to be preserved - you can''t do that in VM86 mode!
So
> registers set in protected mode are "reset" when re-entering
real-mode.
> This makes "big real mode" tricks fail [big real mode is really
just
> going into protected mode, setting a segment to base=0, limit >
0xFFFFFFFF, and returning to real-mode - this allows real-mode code to
> access all of the first 4GB of memory without any problems, rather than
> being limited to 1MB]. Big real-mode is used by many boot-loaders. 
> 
Thank you Mats, for this explanation.

I was aware that problem with FreeBSD in domU 
is related to "big real mode", 
but you gave many interesting details.

Question.
May I try to use GRUB to load FreeBSD kernel
and to circumvent problem with big real mode
that I face when use traditional FreeBSD /boot/loader?
What do you think about it?

> So as a conclusion, the difference here is the internal architecture of
> the processor. AMD choose the "clever way", I think. 
> 
If I understand you right, 
there are no problems with running real-mode guests on 
AMD processors at all?


And another question:

Does anybody know something about running of such rare (for the
present) legacy operating systems, like:

* Windows NT 4
* Windows 95/98
* OS/2

and not legacy, but rare (comparing to Windows and Linux)

* OpenBSD
* MINIX
and 
* Plan 9?

(I ask about running named OS as full virtual guests on a host with
HVM-capable AMD CPU)




Particular question about Plan 9.
As far as I know Plan 9 works well as paravirtualized guest
in Xen 2.
But what about Xen 3?








> --
> Mats
> 
> 
> 
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
-- 
WBR, i.m.chubin


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http://lists.xensource.com/xen-users

> -----Original Message-----
> From: Igor Chubin [mailto:igor@chub.in] 
> Sent: 31 May 2007 11:55
> To: Petersson, Mats
> Cc: Igor Chubin; Mark Williamson; xen-users@lists.xensource.com
> Subject: Re: [Xen-users] xen over quemu OR quemu in Xen domU 
> on a system with HVM-capable CPU
> 
> ...
> > > > Ah.  I have an AMD-V box that works with FreeBSD 6 OK...  
> > > Are you running on 
> > > > an Intel VT-x box?
> > > > 
> > > 
> > > Yes.
> > > At this moment I use Intel VT-x box for my experiments
> > > (Hewlett-Packard DL380 G5 to be more precise).
> > > 
> > > But I can change my hardware if I''ll have good reasons
for this.
> > > The fact that FreeBSD runs in Xen domU''s on hosts with
AMD CPUs,
> > > but not run on hosts with Intel CPUs is very serious, as for me.
> > > 
> > > (May it be that the main reason why FreeBSD runs on one 
> system [AMD]
> > > but does not want to run on another [Intel] is not CPU, 
> but BIOS or
> > > something else?)
> > 
> > HVM domains do not use the BIOS in the machine they are 
> running on at
> > all, so any BIOS difference should be completely ignored. 
> > 
> > In this particular case, I''m pretty sure the reason why it 
> doesn''t work
> > is that Intel''s VT doesn''t support real-mode guests.
Instead, they
> > emulate realmode in VM86 mode (so the processor is in 
> protected 32-bit
> > mode, but running 16-bit real-mode style code). This works 
> as long as
> > the instructions aren''t "ring 0" instructions -
when these
> instructions
> > are seen, they trap with a GP-fault. This is then handled in the
> > VMXassist code that emulates the relevant instruction. This is also
> > fine. The problem occurs when a transition is made from real mode to
> > protected mode and back again, where the registers 
> (particular segment
> > registers) need to be preserved - you can''t do that in VM86
mode! So
> > registers set in protected mode are "reset" when 
> re-entering real-mode.
> > This makes "big real mode" tricks fail [big real mode is
really just
> > going into protected mode, setting a segment to base=0, limit >
> 0xFFFFFFFF, and returning to real-mode - this allows
> real-mode code to
> > access all of the first 4GB of memory without any problems, 
> rather than
> > being limited to 1MB]. Big real-mode is used by many boot-loaders. 
> > 
> 
> Thank you Mats, for this explanation.
> 
> I was aware that problem with FreeBSD in domU 
> is related to "big real mode", 
> but you gave many interesting details.
> 
> Question.
> May I try to use GRUB to load FreeBSD kernel
> and to circumvent problem with big real mode
> that I face when use traditional FreeBSD /boot/loader?
> What do you think about it?
> 
> 
> > So as a conclusion, the difference here is the internal 
> architecture of
> > the processor. AMD choose the "clever way", I think. 
> > 
> 
> If I understand you right, 
> there are no problems with running real-mode guests on 
> AMD processors at all?
> 
> 
> And another question:
> 
> Does anybody know something about running of such rare (for the
> present) legacy operating systems, like:
> 
> * Windows NT 4
I tried this just a few weeks ago. Worked for the limited amount of
testing I gave it. 
> * Windows 95/98
I''ve got a disk sitting around, but I''ve not tested it. I
spent a few
minutes now trying to get it to run, but it seems to not do so - not
sure why. 
> * OS/2
I haven''t tested myself, but list-member Trolle Selander is using this
combination for commercial purposes. 
> 
> and not legacy, but rare (comparing to Windows and Linux)
> 
> * OpenBSD
> * MINIX
> and 
> * Plan 9?
I haven''t tried any of them. The problem(s) with using
"unknown" OS''s is
that they may perform operations that aren''t supported by the HVM part
of Xen - it''s usually not THAT hard to fix, but it can be sometimes...
:-(

--
Mats
> 
> (I ask about running named OS as full virtual guests on a host with
> HVM-capable AMD CPU)
> 
> 
> 
> 
> Particular question about Plan 9.
> As far as I know Plan 9 works well as paravirtualized guest
> in Xen 2.
> But what about Xen 3?
> 
> 
> 
> 
> 
> 
> 
> 
> 
> > --
> > Mats
> > 
> > 
> > 
> > 
> > _______________________________________________
> > Xen-users mailing list
> > Xen-users@lists.xensource.com
> > http://lists.xensource.com/xen-users
> 
> -- 
> WBR, i.m.chubin
> 
> 
> 
> 


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> and not legacy, but rare (comparing to Windows and Linux)
>
> * OpenBSD
> * MINIX
> and
> * Plan 9?
>
> (I ask about running named OS as full virtual guests on a host with
> HVM-capable AMD CPU)
Not tried any of these as fully virtual guests.  However, I''d like to
note
that Minix was ported (at least partially) to Xen by Ivan Kelly.  I think he 
targetted Xen 2 originally, but he was certainly interested in knowing Xen 3 
stuff at the time.

OpenBSD has been ported to run on Xen 3, but I''m not sure what the
status of
that port is.

Plan 9''s own website includes a howto for getting Plan 9 natively
running on
Xen.
> Particular question about Plan 9.
> As far as I know Plan 9 works well as paravirtualized guest
> in Xen 2.
> But what about Xen 3?
The port was updated for Xen 3 (non-PAE), I have a working install here which 
I access using Linux drawterm (a Linux implementation of the plan9 network 
display thingy) - seems fine.

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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On Do, Mai 31, 2007 at 04:24:30 +0100, Mark Williamson
wrote:
> > and not legacy, but rare (comparing to Windows and Linux)
> >
> > * OpenBSD
> > * MINIX
> > and
> > * Plan 9?
> >
> > (I ask about running named OS as full virtual guests on a host with
> > HVM-capable AMD CPU)
> 
> Not tried any of these as fully virtual guests.  However, I''d like
to note
> that Minix was ported (at least partially) to Xen by Ivan Kelly.  I think
he
> targetted Xen 2 originally, but he was certainly interested in knowing Xen
3
> stuff at the time.
> 
> OpenBSD has been ported to run on Xen 3, but I''m not sure what the
status of
> that port is.
Very good news!
Thank you.

I''ve googled and find this pages:
* [http://ropersonline.com/openbsd/xen/openbsd-xen-howto OpenBSD Xen HOWTO]
* [http://marc.info/?l=openbsd-misc&m=115020845610220&w=2 HOWTO Run
OpenBSD/amd64 port for Xen]

May be the links will be useful for somebody.

> 
> Plan 9''s own website includes a howto for getting Plan 9 natively
running on
> Xen.
> 
> > Particular question about Plan 9.
> > As far as I know Plan 9 works well as paravirtualized guest
> > in Xen 2.
> > But what about Xen 3?
> 
> The port was updated for Xen 3 (non-PAE), I have a working install here
which
> I access using Linux drawterm (a Linux implementation of the plan9 network 
> display thingy) - seems fine.
> 

non-PAE?

And what about 64 bit hosts?


Oh!
I forgot GNU/Hurd.
As far as I know GNU/Hurd can run as Xen guest?
At least I have seen page where described how to use GRUB to run 
GNU/Hurd in Xen domain
[http://osdir.com/ml/boot-loaders.grub.devel/2007-01/msg00002.html].
So I''ve decided that GNU/Hurd can run inside Xen.

Am I right?
> Cheers,
> Mark
> 
> -- 
> Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
> Mark: To answer a question with a question: What use is a skateboard?
> Dave: Skateboards have wheels.
> Mark: My wheel has a wheel!
-- 
WBR, i.m.chubin


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> > Plan 9''s own website includes a howto for getting Plan 9
natively running
> > on Xen.
> >
> > > Particular question about Plan 9.
> > > As far as I know Plan 9 works well as paravirtualized guest
> > > in Xen 2.
> > > But what about Xen 3?
> >
> > The port was updated for Xen 3 (non-PAE), I have a working install
here
> > which I access using Linux drawterm (a Linux implementation of the
plan9
> > network display thingy) - seems fine.
>
> non-PAE?
>
> And what about 64 bit hosts?
I don''t believe it''ll work on 64-bit either :-(

Actually, OpenBSD (and probably other "minority" ports like NetBSD,
the
development code for FreeBSD, GNU/Hurd) probably expects to run on 32-bit 
non-PAE as well.
> Oh!
> I forgot GNU/Hurd.
> As far as I know GNU/Hurd can run as Xen guest?
> At least I have seen page where described how to use GRUB to run
> GNU/Hurd in Xen domain
> [http://osdir.com/ml/boot-loaders.grub.devel/2007-01/msg00002.html]. So
> I''ve decided that GNU/Hurd can run inside Xen.
>
> Am I right?
Yes, Hurd does can on Xen.  I managed to build GNU Mach and boot it on Xen, 
but haven''t managed to get the Hurd running on top of it. 
I''ve not heard
much about this port for a while, though.

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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