linux-kernel - Re: [Xen-devel] [PATCH] xen: point xen_start_info to a dummy struct for PV on HVM guests

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Message-ID: <alpine.DEB.2.02.1210031450220.29232@kaball.uk.xensource.com>
Date:	Wed, 3 Oct 2012 14:51:59 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Ian Campbell <Ian.Campbell@...rix.com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH] xen: point xen_start_info to a dummy struct
 for PV on HVM guests

On Wed, 3 Oct 2012, Ian Campbell wrote:
> On Wed, 2012-10-03 at 14:37 +0100, Stefano Stabellini wrote:
> > PV on HVM guests don't have a start_info page mapped by Xen, so
> > xen_start_info is just NULL for them.
> > That is problem because other parts of the code expect xen_start_info to
> > point to something valid, for example xen_initial_domain() is defined as
> > follow:
> > 
> > #define xen_initial_domain()    (xen_domain() && \
> >                  xen_start_info->flags & SIF_INITDOMAIN)
> 
> But anyone who calls this before xen_start_info is setup is going to get
> a bogus result, specifically in this case they will think they are domU
> when in reality they are dom0 -- wouldn't it be better to fix those
> callsites?

That cannot be the case because setting up xen_start_info is the very
first thing that is done, before even calling to C.


> Perhaps turn this into a static inline with a BUG_ON(!xen_start_info) to
> make catching these cases easier?

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