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64 bit guest on 64 bit host (without VMX?)

Posted: 10. Mar 2009, 11:53
by pwaller
Hi,

I'm running on an Acer laptop, and unfortunately it seems (I understand after an exchange of e-mails with their exiguous support*) that Acer saw fit to disable VT-x in the BIOS and not provide an option to enable it. As far as I am aware this means that in order to enable this feature which the CPU does support, someone would have to reverse engineer the BIOS and prevent it from setting a single "lock-bit" with a WRMSR instruction.

Does this mean it is impossible to run a 64 bit guest without said BIOS hack? I seem to be experiencing a significant performance penalty running Ubuntu 32-bit under Vista 64-bit.

Thanks for any information.

* From Acer: "I understand what your [sic] saying but the BIOS will not support this software and as of yet there are no plans by ACER to release a BIOS update that will support the VT software"

Re: 64 bit guest on 64 bit host (without VMX?)

Posted: 10. Mar 2009, 12:23
by vbox4me2
Read the manual about 64bit guest support and a 32bit host.
As for the bios, have a look at http://www.coreboot.org/Welcome_to_coreboot

Re: 64 bit guest on 64 bit host (without VMX?)

Posted: 10. Mar 2009, 12:29
by pwaller
I saw this line in the manual:

"On 64-bit hosts, 64-bit guest support is always enabled, so you can simply install
a 64-bit operating system in the guest."

But when I try to start a 64-bit Ubuntu LiveCD on my 64-bit vista host, linux bails out complaining it only found an i686 CPU rather than a 64-bit one?

coreboot sounds nice but doesn't look like it comes close to supporting my machine..

Re: 64 bit guest on 64 bit host (without VMX?)

Posted: 10. Mar 2009, 12:44
by vbox4me2
See "1.6 64-bit guests" about the requirements, ea. "In detail, 64-bit guests are supported under the following conditions:", etc...

Re: 64 bit guest on 64 bit host (without VMX?)

Posted: 10. Mar 2009, 12:52
by pwaller
Sorry, I was confused by the manual for some reason. I thought that VMX was optional (as it says earlier in the manual), but I guess that is not the case for 64-bit OSes?

So I do need VT-x to do any 64 bit virtualization? Is this just a virtualbox limitation, or a general one?

Should I expect a big performance hit running a 32-bit GUEST under a 64-bit host? Ubuntu took over an hour to install on my powerful laptop, I've never seen it so slow.

Re: 64 bit guest on 64 bit host (without VMX?)

Posted: 10. Mar 2009, 13:36
by vbox4me2
You need vt-x for 64bit support, thats not specific to vbox, its how 64bit architecture works. There are some 64bit emulators.
32bit Guests run fine under a 64bit Host, ubuntu is just slow installing and starting, once running its ok though.