Xen devel - Jan 2008 - Early test for Windows vs Linux hvm domain?

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@cl.cam.ac.uk]
> Sent: Wednesday, January 30, 2008 1:21 AM
> To: dan.magenheimer@oracle.com; Samuel Thibault
> Cc: xen-devel@lists.xensource.com
> Subject: Re: [Xen-devel] Early test for 32- vs 64-bit hvm domain?
> 
> 
> On 30/1/08 00:34, "Dan Magenheimer" 
> <dan.magenheimer@oracle.com> 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
> 
> 
> 

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

> 
> 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).
> 
You may have mentioned it in your other thread, but what exactly is the
problem you are trying to solve here?

I would say that the answer is definitely no, depending on what your
definition of ''early'' is. A hvm domain could invoke grub, and
then a
user could then choose to run windows or Linux (or BSD, or another OS
altogether). Does DOS work under HVM? If it does, a HVM domain could
start DOS, the user could spend a bit of time in there, and then later
on launch Linux from there.

James


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

For my purposes, the definition of ''early'' is before the
launched guest
expects to be doing any (accurate) timekeeping.

I''m experimenting with the mechanisms in Xen for handling virtual time.
At this point, I''m looking for heuristics, not 100% accuracy, and want
to divine in hvm code whether Windows is running or Linux is running
(and, yes, I realize there are other possibilities :-)

Thanks,
Dan Magenheimer

If Xen could save time in a bottle / then clocks wouldn''t virtually
skew /
It would save every tick / for VMs that aren''t quick /
and Xen then would send them anew
(by Dan Magenheimer... with apologies to the late great Jim Croce)
> -----Original Message-----
> From: James Harper [mailto:james.harper@bendigoit.com.au]
> Sent: Wednesday, January 30, 2008 5:17 PM
> To: dan.magenheimer@oracle.com; Xen-Devel (E-mail)
> Subject: RE: [Xen-devel] Early test for Windows vs Linux hvm domain?
> 
> 
> > 
> > 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).
> > 
> 
> You may have mentioned it in your other thread, but what 
> exactly is the
> problem you are trying to solve here?
> 
> I would say that the answer is definitely no, depending on what your
> definition of ''early'' is. A hvm domain could invoke grub,
and then a
> user could then choose to run windows or Linux (or BSD, or another OS
> altogether). Does DOS work under HVM? If it does, a HVM domain could
> start DOS, the user could spend a bit of time in there, and then later
> on launch Linux from there.
> 
> James
> 
> 

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