Laptops and hardware virtualization

[jarod-ajLrJawYSntWk0Htik3J/w at public.gmane.org (Jarod Wilson)]

On Mon, Feb 15, 2010 at 11:06 AM, Richard Pieri <richard.pieri-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org> wrote:
> On Feb 14, 2010, at 5:32 PM, Scott Ehrlich wrote:
>>
>> What is the desired end result? ? As I learned from this list, among
>> others, the VT support in BIOS only appears to affect the ability of
>> the system to run a 64-bit VM. ?Am I missing something else? ? ?Was
>> there something in the original question of the OP I lost track of?
>
> I'm going to simplify things a bit...
>
> Usually, the hypervisor (whether type 1 or type 2) runs in privileged mode and guest operating systems run in non-privileged mode. ?When a guest attempts to execute a privileged instruction the CPU throws an exception. ?The hypervisor traps that exception and emulates the instruction in some manner, passing the result back to the guest. ?The technique is called "trap and emulate".
>
> The problem -- I should say one of the problems -- with the x86 architecture is that there are a slew of privileged instructions that don't generate exceptions in non-privileged mode. ?The way that VMware and others got around that was by emulating an entire x86 CPU in the hypervisor. ?If you ever used older versions of VMware Desktop then you're familiar with the CPU load that the virtual machine incurs.
>
> Along come AMD-V and VT-x. ?These extensions to the x86 architecture provide wrappers around some (but not all) of those privileged instructions. ?These wrappers generate exceptions in non-privileged mode. ?The hypervisor can trap the exceptions and emulate them. ?If you've used VMware or VirtualBox or Parallels on a recent system with the virtualization extensions then you've seen how low the VM overhead is. ?If you cannot enable the extensions then the hypervisor has to fall back to CPU emulation.
>
> Which brings me to the answer. ?You can't run 64-bit guests without AMD-V/VT-x because the CPU emulators do not emulate 64-bit instructions.

Only, yes, you can. As I said elsewhere in this thread yesterday, the
first-gen AMD Opteron processors, which have no AMD-V, *do* in fact
support 64-bit guests under VMware.

-- 
Jarod Wilson
jarod-ajLrJawYSntWk0Htik3J/w at public.gmane.org