[Qemu-devel] [Bug 596106] [NEW] kvm to emulate 64 bit cpu on 32 bit host

[Qemu-devel] [Bug 596106] [NEW] kvm to emulate 64 bit cpu on 32 bit host

[dennyhalim.com]

Public bug reported:

i wish kvm can run 64bit guest os on 32bit host just like qemu does.

** Affects: qemu
     Importance: Undecided
         Status: New


** Tags: kvm

** Tags added: kvm

-- 
kvm to emulate 64 bit cpu on 32 bit host
https://bugs.launchpad.net/bugs/596106
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.

Status in QEMU: New

Bug description:
i wish kvm can run 64bit guest os on 32bit host just like qemu does.

[Qemu-devel] [Bug 596106] Re: kvm to emulate 64 bit cpu on 32 bit host

[Iggy]

KVM isn't an emulator. It virtualizes the CPU. A 32bit CPU can't be
forced to run as a 64bit cpu. This is a wontfix.

-- 
kvm to emulate 64 bit cpu on 32 bit host
https://bugs.launchpad.net/bugs/596106
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.

Status in QEMU: New

Bug description:
i wish kvm can run 64bit guest os on 32bit host just like qemu does.

Re: [Qemu-devel] [Bug 596106] Re: kvm to emulate 64 bit cpu on 32 bit host

[Avi Kivity]

On 06/19/2010 01:53 AM, Iggy wrote:
> KVM isn't an emulator. It virtualizes the CPU. A 32bit CPU can't be
> forced to run as a 64bit cpu. This is a wontfix.
>
>    

qemu actually supports this (32-bit qemu can run a 64-bit guest with 
kvm, provided that the kernel is 64-bit).

So as well as a wontfix, it's filed in the wrong tracker.

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

[Qemu-devel] [Bug 596106] Re: kvm to emulate 64 bit cpu on 32 bit host

[Anthony Liguori]

Thanks for the request.  It's certainly possible with most modern
distributions to just install a 64-bit kernel with a 32-bit userspace.
Technically speaking, 64-bit guests in a 32-bit kernel is prohibitively
difficult.

** Changed in: qemu
       Status: New => Won't Fix

-- 
kvm to emulate 64 bit cpu on 32 bit host
https://bugs.launchpad.net/bugs/596106
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.

Status in QEMU: Won't Fix

Bug description:
i wish kvm can run 64bit guest os on 32bit host just like qemu does.

[Qemu-devel] [Bug 596106] Re: kvm to emulate 64 bit cpu on 32 bit host

[Natalia Portillo]

VMWare is able to do it, we should be able.

-- 
kvm to emulate 64 bit cpu on 32 bit host
https://bugs.launchpad.net/bugs/596106
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.

Status in QEMU: Won't Fix

Bug description:
i wish kvm can run 64bit guest os on 32bit host just like qemu does.

[Qemu-devel] Re: [Bug 596106] Re: kvm to emulate 64 bit cpu on 32 bit host

[Paolo Bonzini]

On 06/19/2010 03:01 PM, Natalia Portillo wrote:
> VMWare is able to do it, we should be able.

They do it like TCG does it, not like KVM.

Paolo

Re: [Qemu-devel] Re: [Bug 596106] Re: kvm to emulate 64 bit cpu on 32 bit host

[Jamie Lokier]

Paolo Bonzini wrote:
> On 06/19/2010 03:01 PM, Natalia Portillo wrote:
> >VMWare is able to do it, we should be able.
> 
> They do it like TCG does it, not like KVM.

I heard rumours VMWare use KVM-style chip virtualisation when running
a 64-bit guest on a 32-bit host kernel on 64-bit hardware.

If true, that makes particular sense for Windows host users, who can't
just drop in a 64-bit host kernel without breaking their userspace
thoroughly.  (If it was that easy, 64-bit Windows wouldn't use
a surruptitious VM to run 32-bit apps :-).

It seems like a good way for Windows users to run a single 64-bit app
on an otherwise 32-bit system that's working fine.

On Linux hosts I would expect you can drop in a 64-bit kernel, while
continuing to run a 32-bit userspace.  But I don't know if (a) that's
entirely true, and (b) if distro packaging blocks that sort of thing
from being easy.

Unfortunately even that doesn't help people who just want to run a
64-bit VM as an ordinary user and aren't permitted to change their
Linux host kernel, e.g. a shared system, or some rented servers.

-- Jamie

Re: [Qemu-devel] [Bug 596106] Re: kvm to emulate 64 bit cpu on 32 bit host

[Andrew Cathrow]

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----- "Natalia Portillo" <claunia@claunia.com> wrote: 
> From: "Natalia Portillo" <claunia@claunia.com> 
> To: qemu-devel@nongnu.org 
> Sent: Saturday, June 19, 2010 9:01:04 AM GMT -05:00 US/Canada Eastern 
> Subject: [Qemu-devel] [Bug 596106] Re: kvm to emulate 64 bit cpu on 32 bit host 
> 
> VMWare is able to do it, we should be able. 

VMware can't do that! 
To run a 64bit guest on VMware you need 64bit hardware and VT/AMD-V 
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1003945 




> 
> -- 
> kvm to emulate 64 bit cpu on 32 bit host 
> https://bugs.launchpad.net/bugs/596106 
> You received this bug notification because you are a member of qemu- 
> devel-ml, which is subscribed to QEMU. 
> 
> Status in QEMU: Won't Fix 
> 
> Bug description: 
> i wish kvm can run 64bit guest os on 32bit host just like qemu does. 
> 
> 
> 
> 

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Re: [Qemu-devel] [Bug 596106] Re: kvm to emulate 64 bit cpu on 32 bit host

[Natalia Portillo]

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El 19/06/2010, a las 22:12, Andrew Cathrow escribió:

> 
> 
> 
> 
> ----- "Natalia Portillo" <claunia@claunia.com> wrote: 
> > From: "Natalia Portillo" <claunia@claunia.com>
> > To: qemu-devel@nongnu.org
> > Sent: Saturday, June 19, 2010 9:01:04 AM GMT -05:00 US/Canada Eastern
> > Subject: [Qemu-devel] [Bug 596106] Re: kvm to emulate 64 bit cpu on 32 bit host
> >
> > VMWare is able to do it, we should be able.
> 
> VMware can't do that!
> To run a 64bit guest on VMware you need 64bit hardware and VT/AMD-V
> http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1003945

You got the point wrong, I'm talking running WITH 64 bit hardware in a 32 bit guest.

This is done in Mac OS X Leopard (kernel is only 32 bit) and Mac OS X Snow Leopard (using 32 bit kernel not 64 bit one) by VMWare, Parallels and VirtualBox, as well as on Windows 32 bit using VMWare (dunno about VBox and Parallels, VirtualPC is unable to run 64 bit guests at all even on 64 bit hosts), just provided of course, the hardware is 64 bit.

> > 
> > -- 
> > kvm to emulate 64 bit cpu on 32 bit host
> > https://bugs.launchpad.net/bugs/596106
> > You received this bug notification because you are a member of qemu-
> > devel-ml, which is subscribed to QEMU.
> > 
> > Status in QEMU: Won't Fix
> > 
> > Bug description:
> > i wish kvm can run 64bit guest os on 32bit host just like qemu does.
> > 
> > 
> > 
> >


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Re: [Qemu-devel] [Bug 596106] Re: kvm to emulate 64 bit cpu on 32 bit host

[Jamie Lokier]

Natalia Portillo wrote:
>    You got the point wrong, I'm talking running WITH 64 bit hardware in a
>    32 bit guest.
>    This is done in Mac OS X Leopard (kernel is only 32 bit) and Mac OS X
>    Snow Leopard (using 32 bit kernel not 64 bit one) by VMWare, Parallels
>    and VirtualBox, as well as on Windows 32 bit using VMWare (dunno about
>    VBox and Parallels, VirtualPC is unable to run 64 bit guests at all
>    even on 64 bit hosts), just provided of course, the hardware is 64
>    bit.

Ah yes, Mac OS X too.

Apart from breaking userspace, the other reason people stick with
32-bit host kernels on both Windows and Macs is the 64-bit device
drivers often don't work properly, or aren't available at all.  They
continue to improve, but still aren't as mature and dependable as
32-bit drivers.

This is also true of Linux 64-bit kernels - both bugs and unavailable
third party drivers/firmware.  (But less so than the other OSes.)
So even with Linux people cannot assume dropping in a 64-bit host
kernel is always free of kernel/driver issues.

Marking this feature request "won't fix" is just a statement that KVM
developers aren't inclined to support this feature.

But there's nothing to stop an interested contributor having a go.
I'm sure if it works and the code is clean enough it will be accepted.

>    VirtualPC is unable to run 64 bit guests at all even on 64 bit
>    hosts

Are you sure?  Microsoft provides numerous downloadable 64-bit guest
Windows images, and VirtualPC is Microsoft's; they must be running on
something.

-- Jamie

Re: [Qemu-devel] [Bug 596106] Re: kvm to emulate 64 bit cpu on 32 bit host

[Natalia Portillo]

Paolo said:
> They do it like TCG does it, not like KVM.

You are wrong, and it's easy to check as the speed is almost native.
Having emulation would make it slow as hell.

Jamie said:
> 
>>   VirtualPC is unable to run 64 bit guests at all even on 64 bit
>>   hosts
> 
> Are you sure?  Microsoft provides numerous downloadable 64-bit guest
> Windows images, and VirtualPC is Microsoft's; they must be running on
> something.
> 

That may be in Windows Virtual PC (that requires VT and Windows 7 Ultimate/Professional, and is a feature of that OSes not a separate product) or Hyper-V (again, requires VT and is a feature of Windows 2008 Server), but not on the standalone Microsoft Virtual PC 2007.


It is fully possible to run 64-bit code in a 32-bit kernel, Mac OS X Leopard does that all the way without problems, and VMWare found how to do the trick with the NT kernel.

The question is not "is it possible to make KVM run 64-bit code in a 32-bit kernel?" (it is), the question is, "the people in charge of KVM want to add this feature?".

Personally I don't believe so, neither I am on the "do it" side, I'm just saying it is technically possible.

Natalia Portillo