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Date: Wed, 1 Aug 2012 17:21:00 +0100
From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
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To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
CC: Ian Campbell <Ian.Campbell@citrix.com>,
        Stefano Stabellini <Stefano.Stabellini@eu.citrix.com>,
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Subject: Re: [PATCH 13/24] xen/arm: get privilege status
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On Wed, 1 Aug 2012, Konrad Rzeszutek Wilk wrote:
> On Fri, Jul 27, 2012 at 03:33:50PM +0100, Ian Campbell wrote:
> > On Fri, 2012-07-27 at 15:25 +0100, Stefano Stabellini wrote:
> > > On Fri, 27 Jul 2012, Ian Campbell wrote:
> > > > On Thu, 2012-07-26 at 16:33 +0100, Stefano Stabellini wrote:
> > > > > Use Xen features to figure out if we are privileged.
> > > > > 
> > > > > XENFEAT_dom0 was introduced by 23735 in xen-unstable.hg.
> > > > > 
> > > > > Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> > > > > ---
> > > > >  arch/arm/xen/enlighten.c         |    7 +++++++
> > > > >  include/xen/interface/features.h |    3 +++
> > > > >  2 files changed, 10 insertions(+), 0 deletions(-)
> > > > > 
> > > > > diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> > > > > index dc68074..2e013cf 100644
> > > > > --- a/arch/arm/xen/enlighten.c
> > > > > +++ b/arch/arm/xen/enlighten.c
> > > > > @@ -2,6 +2,7 @@
> > > > >  #include <xen/interface/xen.h>
> > > > >  #include <xen/interface/memory.h>
> > > > >  #include <xen/platform_pci.h>
> > > > > +#include <xen/features.h>
> > > > >  #include <asm/xen/hypervisor.h>
> > > > >  #include <asm/xen/hypercall.h>
> > > > >  #include <linux/module.h>
> > > > > @@ -58,6 +59,12 @@ int __init xen_guest_init(void)
> > > > >  	}
> > > > >  	xen_domain_type = XEN_HVM_DOMAIN;
> > > > >  
> > > > > +	xen_setup_features();
> > > > > +	if (xen_feature(XENFEAT_dom0))
> > > > > +		xen_start_info->flags |= SIF_INITDOMAIN|SIF_PRIVILEGED;
> > > > > +	else
> > > > > +		xen_start_info->flags &= ~(SIF_INITDOMAIN|SIF_PRIVILEGED);
> > > > 
> > > > What happens here on platforms prior to hypervisor changeset 23735?
> > > 
> > > It wouldn't work.
> > > Considering that we are certainly not going to backport ARM support to
> > > Xen 4.1, and that both ARM and XENFEAT_dom0 will be present in Xen 4.2,
> > > do we really need to support the Xen unstable changesets between ARM was
> > > introduced and XENFEAT_dom0 appeared?
> 
> So should it just panic and say "AAAAAAH"?

I could panic if I find out that XENFEAT_dom0 is unimplemented but
actually I only get to know if it is available...