[Xen-devel] Pre-virtualization, was Re: linux/arch/xen/i386 or linux/arch/i386/xen

[Joshua LeVasseur <jtl@xxxxxxxxxx>]

On May 18, 2005, at 17:09, Magenheimer, Dan (HP Labs Fort Collins)  
wrote:
> There have been various discussions on this list about
> "transparent paravirtualization", i.e. the ability for
> a paravirtualized kernel to run both as a guest of Xen
> and on bare metal.  This is definitely an objective of
> Xen/ia64.  Nobody has tried it for Xen/x86, but if it
> can be done, I'm sure commercial companies and distros
> would be eager to utilize it (one less set of bits to
> support).
Thanks for the lead-in Dan.  As mentioned before on this list, we  
have an automated, pre-virtualization solution that permits a single  
binary to execute on bare x86 hardware and on various hypervisors,  
with good performance.  See the original message:
http://lists.xensource.com/archives/html/xen-devel/2005-04/msg00163.html

We have now released our source code.  For our project web page,  
source code (BSD license), and a script to build everything, see:
http://l4ka.org/projects/virtualization/afterburn/
We tried to minimize the overhead for getting started, but we can't  
automate the parts that are dependent on the final hardware, and thus  
some tenacious debug skills may be necessary.  Also see the user's  
manual.
Note that our project does use some concepts of transparent para- 
virtualization, primarily to deal with higher-level OS concepts.   
Capturing higher-level OS concepts is particularly useful when  
mapping guest OS concepts to hypervisor concepts, as is common on  
more traditional kernels, such as executing at user-level on Linux,  
Windows NT, and our L4 microkernel.  Transparent virtualization isn't  
really used on our internal Xen infrastructure (although in our  
public CVS, it is used a little).
> In many ways, a "xen" subdirectory is much more like
> a "pci" or "math-emu" subdirectory, than a subarch.
> For example, mach-es7000 and xen may need to co-exist
> in the same kernel.
>
> So, mach-xen may be a poor choice.  A subtle distinction
> perhaps but when dealing with Linux kernel developers,
> purity of thinking may avoid future patch submission
> arguments.
With pre-virtualization, the modifications to the guest OS are very  
minor.  The whole point is to automate the para-virtualization.  So  
for example, a single binary can execute on the Xen hypervisor, or as  
a user-level Linux application, without using any of the user-mode  
Linux support currently in Linux, and without requiring the proposed  
additions to Linux for Xen.
-Josh




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