Re: [patch 14/21] Xen-paravirt: Add XEN config options and disable unsupported config options.

[Zachary Amsden <zach@vmware.com>]

Jeremy Fitzhardinge wrote:
> The XEN config option enables the Xen paravirt_ops interface, which is
> installed when the kernel finds itself running under Xen. (By some
> as-yet fully defined mechanism, implemented in a future patch.)
>
> Xen is no longer a sub-architecture, so the X86_XEN subarch config
> option has gone.
>
> The disabled config options are:
> - PREEMPT: Xen doesn't support it
> - HZ: set to 100Hz for now, to cut down on VCPU context switch rate.
>   This will be adapted to use tickless later.
> - kexec: not yet supported
>
> Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
> Signed-off-by: Ian Pratt <ian.pratt@xensource.com>
> Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
> Signed-off-by: Chris Wright <chrisw@sous-sol.org>
>   

We do support different HZ values, although 100HZ is actually preferable 
for us, so I don't object to that.  PREEMPT is supported by us, but not 
as tested as I would like, so I also don't object to dropping it for 
generic paravirt guests - Rusty - Avi any objections to dropping preempt 
in terms of lguest/KVM paravirtualization?

Paravirt-ops definitely needs a hook for kexec, although we should not 
disable kexec for the natively booted paravirt-ops.  Eric - is there a 
way to disable it at runtime?

We do support the doublefault task gate, and it would be good to keep 
it, but I can't complain so much if it is gone from generic paravirt 
kernels for now, because it is non-essential, and generally fatal 
anyway.  We do need it for native boots of paravirt-ops kernels, 
however, so turning off the config option still needs to be revisited.

Zach