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

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Message-ID: <alpine.DEB.2.02.1401051718020.8667@kaball.uk.xensource.com>
Date:	Sun, 5 Jan 2014 17:18:19 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Mukesh Rathor <mukesh.rathor@...cle.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.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, Mukesh Rathor wrote:
> On Wed, 18 Dec 2013 16:17:39 -0500
> Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote:
> 
> > On Wed, Dec 18, 2013 at 06:31:43PM +0000, Stefano Stabellini wrote:
> > > On Tue, 17 Dec 2013, Konrad Rzeszutek Wilk wrote:
> > > > From: Mukesh Rathor <mukesh.rathor@...cle.com>
> > > > 
> > > > PVH is a PV guest with a twist - there are certain things
> > > > that work in it like HVM and some like PV. There is
> > > > a similar mode - PVHVM where we run in HVM mode with
> > > > PV code enabled - and this patch explores that.
> > > > 
> > > > The most notable PV interfaces are the XenBus and event channels.
> > > > For PVH, we will use XenBus and event channels.
> > > > 
> > > > For the XenBus mechanism we piggyback on how it is done for
> > > > PVHVM guests.
> > > > 
> > > > Ditto for the event channel mechanism - we piggyback on PVHVM -
> > > > by setting up a specific vector callback and that
> > > > vector ends up calling the event channel mechanism to
> > > > dispatch the events as needed.
> > > > 
> > > > This means that from a pvops perspective, we can use
> > > > native_irq_ops instead of the Xen PV specific. Albeit in the
> > > > future we could support pirq_eoi_map. But that is
> > > > a feature request that can be shared with PVHVM.
> > > > 
> > > > Signed-off-by: Mukesh Rathor <mukesh.rathor@...cle.com>
> > > > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > > > ---
> > > >  arch/x86/xen/enlighten.c           | 6 ++++++
> > > >  arch/x86/xen/irq.c                 | 5 ++++-
> > > >  drivers/xen/events.c               | 5 +++++
> > > >  drivers/xen/xenbus/xenbus_client.c | 3 ++-
> > > >  4 files changed, 17 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> > > > index e420613..7fceb51 100644
> > > > --- a/arch/x86/xen/enlighten.c
> > > > +++ b/arch/x86/xen/enlighten.c
> > > > @@ -1134,6 +1134,8 @@ void xen_setup_shared_info(void)
> > > >  	/* In UP this is as good a place as any to set up shared
> > > > info */ xen_setup_vcpu_info_placement();
> > > >  #endif
> > > > +	if (xen_pvh_domain())
> > > > +		return;
> > > >  
> > > >  	xen_setup_mfn_list_list();
> > > >  }
> > > 
> > > This is another one of those cases where I think we would benefit
> > > from introducing xen_setup_shared_info_pvh instead of adding more
> > > ifs here.
> > 
> > Actually this one can be removed.
> > 
> > > 
> > > 
> > > > @@ -1146,6 +1148,10 @@ void xen_setup_vcpu_info_placement(void)
> > > >  	for_each_possible_cpu(cpu)
> > > >  		xen_vcpu_setup(cpu);
> > > >  
> > > > +	/* PVH always uses native IRQ ops */
> > > > +	if (xen_pvh_domain())
> > > > +		return;
> > > > +
> > > >  	/* xen_vcpu_setup managed to place the vcpu_info within
> > > > the percpu area for all cpus, so make use of it */
> > > >  	if (have_vcpu_info_placement) {
> > > 
> > > Same here?
> > 
> > Hmmm, I wonder if the vcpu info placement could work with PVH.
> 
> It should now (after a patch I sent while ago)... the comment implies
> that PVH uses native IRQs even case of vcpu info placlement...
> 
> perhaps it would be more clear to do:
> 
>         for_each_possible_cpu(cpu)
>                 xen_vcpu_setup(cpu);
>         /* PVH always uses native IRQ ops */
>         if (have_vcpu_info_placement && !xen_pvh_domain) {
>             pv_irq_ops.save_fl = __PV_IS_CALLEE_SAVE(xen_save_fl_direct);
>             .........

Yeah, this looks better
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