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

[Avi Kivity <avi@xxxxxxxxxxxx>]

Zachary Amsden wrote:
> 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@xxxxxxxxxxxxx>
> > Signed-off-by: Ian Pratt <ian.pratt@xxxxxxxxxxxxx>
> > Signed-off-by: Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
> > Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
> >   
> We do support different HZ values, although 100HZ is actually 
> preferable for us, so I don't object to that.  
Ditto for kvm.

> 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?
I don't have any objections myself, but Ingo (who has done the bulk of 
the kvm paravirt work; cc'ed) uses PREEMPT_RT, so he will certainly object.
> 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?
kvm paravirt should work correctly with kexec.

> 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.
kvm doesn't support task gates (a task switch will immediately kill the 
guest).
--
error compiling committee.c: too many arguments to function


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