[Xen-devel] Early test for Windows vs Linux hvm domain?

["Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx>]

Thanks to all for the 32-bit vs 64-bit ideas.  Keir's
EFER LME bit works like a charm.

Now a probably tougher (and more controversial) question:

Is there any algorithm or heuristic early in hvm launch that
can distinguish between a windows guest and a linux guest
(64-bit specifically, but if same or different test works
for 32-bit that would be useful too).

Thanks,
Dan

> -----Original Message-----
> From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx]
> Sent: Wednesday, January 30, 2008 1:21 AM
> To: dan.magenheimer@xxxxxxxxxx; Samuel Thibault
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] Early test for 32- vs 64-bit hvm domain?
> 
> 
> On 30/1/08 00:34, "Dan Magenheimer" 
> <dan.magenheimer@xxxxxxxxxx> wrote:
> 
> >> As long as e.g. Linux has not started (i.e. during bios 
> and grub for
> >> instance), you can't know whether that will be a 64bit Linux
> >> or a 32bit
> >> Linux.
> >
> > That's what I was afraid of...
> >
> > Then what is the earliest point in the execution of an x86_64
> > domain/vcpu in *xen* where hvm_long_mode_enabled(v) will work
> > properly? E.g. in Linux/x86_64 is long mode set early in __start?
> > And is this done via a hypercall or an emulated instruction?
> 
> As sson as you see LME bit get set in the EFER MSR then you 
> know you have a
> 64-bit guest. Writes to EFER are emulated in 
> long_mode_do_msr_write() in
> vmx.c and svm.c. Those are the places to patch in Xen 3.1 branch.
> 
>  -- Keir
> 
> 
>


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