linux-kernel - Re: [Xen-devel] [PATCH v11 09/12] xen/pvh: Piggyback on PVHVM XenBus and event channels for PVH.

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Date:	Fri, 3 Jan 2014 16:29:04 -0800
From:	Mukesh Rathor <mukesh.rathor@...cle.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>,
	<boris.ostrovsky@...cle.com>, <david.vrabel@...rix.com>,
	<jbeulich@...e.com>
Subject: Re: [Xen-devel] [PATCH v11 09/12] xen/pvh: Piggyback on PVHVM
 XenBus and event channels for PVH.

On Fri, 3 Jan 2014 15:04:27 +0000
Stefano Stabellini <stefano.stabellini@...citrix.com> wrote:

> On Tue, 31 Dec 2013, Konrad Rzeszutek Wilk wrote:
> > > > --- a/drivers/xen/xenbus/xenbus_client.c
> > > > +++ b/drivers/xen/xenbus/xenbus_client.c
> > > > @@ -45,6 +45,7 @@
> > > >  #include <xen/grant_table.h>
> > > >  #include <xen/xenbus.h>
> > > >  #include <xen/xen.h>
> > > > +#include <xen/features.h>
> > > >  
> > > >  #include "xenbus_probe.h"
> > > >  
> > > > @@ -743,7 +744,7 @@ static const struct xenbus_ring_ops
> > > > ring_ops_hvm = { 
> > > >  void __init xenbus_ring_ops_init(void)
> > > >  {
> > > > -	if (xen_pv_domain())
> > > > +	if (xen_pv_domain()
> > > > && !xen_feature(XENFEAT_auto_translated_physmap))
> > > 
> > > Can we just change this test to
> > > 
> > > if (!xen_feature(XENFEAT_auto_translated_physmap))
> > > 
> > > ?
> > 
> > No. If we do then the HVM domains (which are also !auto-xlat)
> > will end up using the PV version of ring_ops.
> 
> Actually HVM guests have XENFEAT_auto_translated_physmap, so in this
> case they would get &ring_ops_hvm.

Right. Back then I was confused about all the other PV modes, like
shadow, supervisor, ... but looks like they are all obsolete. It could 
just be:

        if (!xen_feature(XENFEAT_auto_translated_physmap))
                ring_ops = &ring_ops_pv;
        else
                ring_ops = &ring_ops_hvm;

thanks,
Mukesh
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