Xen devel - Feb 2006 - RE: Re: [Xen-changelog] Indirect hypercalls through ahypercall transfer page.

> > The primary reason for this patch is that it will enable us 
> to run a 
> > xenified kernel on bare metal: a ''micro xen'' would
be loaded by the
> > boot loader alongside a xenified kernel image, enabling the 
> kernel to 
> > effectively run on the baremetal at full native performance (though 
> > obviously you could only run one kernel on a machine at a time).
> 
> This is an elegant feature that would have been better 
> introduced with the above explanation rather than a patchbot message.
> 
> If I missed that discussion, apologies.
Mike, there was some discussion about this and the other new ''feature
flags'' at the OS Ports session at the summit (and in particular in the
''linux merge'' breakout group).

The hypercall transfer page is just one of several new feature flags
that should enable us to have a single xen-ified kernel that is capable
of running on bare metal, on pae and non-pae hypervisors, 64b
hypervisor, under HVM etc. Obviously many of these combinations will
require shadow pagetables to be enabled (and hence some loss of
performance), but it will be good to be able to support them.

The main feature flag that is currently missing is one to enable the
kernel''s hypervisor vm hole size to be setable at guest boot time
(necessary for running non-pae kernels on a pae hypervisor). Hopefully
Novell are working on this... :)

Ian
 

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Ian Pratt wrote:
> 
> Mike, there was some discussion about this and the other new
''feature
> flags'' at the OS Ports session at the summit (and in particular in
the
> ''linux merge'' breakout group).
Thanks, I guess I missed that session.
> The hypercall transfer page is just one of several new feature flags
> that should enable us to have a single xen-ified kernel that is capable
> of running on bare metal, on pae and non-pae hypervisors, 64b
A 32-bit kernel running on a 64-bit xen, for example? So in this case 
xen fills the page with 32-bit hcalls?

Mike





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