linux-kernel - Re: [Xen-devel] Re: [PATCH] xen: modify kernel mappings corresponding to granted pages

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Date:	Wed, 10 Aug 2011 09:50:33 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Ian Campbell <Ian.Campbell@...citrix.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Jeremy Fitzhardinge <Jeremy.Fitzhardinge@...rix.com>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>
Subject: Re: [Xen-devel] Re: [PATCH] xen: modify kernel mappings
 corresponding to granted pages

On Wed, Aug 10, 2011 at 09:06:04AM +0100, Ian Campbell wrote:
> On Tue, 2011-08-09 at 16:50 +0100, Konrad Rzeszutek Wilk wrote:
> > > > So I hadn't looked at this in detail, but I wonder if we can use the
> > > > MULTIcall for this? It looks like we need to do two hypercalls so why
> > > > not batch it?
> > > 
> > > That was going to be my next question. We should definitely batch these
> > > if possible.
> > > 
> > > > And while we are it - we could change the MMU ops to only do this on
> > > > initial domain and for the domU case do the old mechanism?
> > > 
> > > We need this in domU for driver domains and the like, don't we?
> > 
> > Sure, but I believe the majority of domU domains would not require this.
> 
> The overhead of this stuff is low if not used, isn't it? Compared with
> the complexity of having domains know if they might be used as a driver
> domain or not that seems like the tradeoff to be aiming for.
> 
> > I was thinking that when we start playing with the device/driver domains
> > we would want to escalate the privilige level (or perhaps not)?
> 
> We don't want any escalation of privilege over and above what is
> necessary to be a driver domain, which is generally none.
> 
> >  Or
> > perhaps introcuce a new type - "if (xen_driver_domain())" to recognize
> > that we are special ?
> 
> Where does the information to set xen_driver_domain == TRUE come from?

No idea. Was just thinking about it.. but you have convienced me it
is not worth looking at.
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