linux-kernel - Re: [PATCH] KVM: allow host header to be included even for !CONFIG

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Date:	Thu, 21 Mar 2013 13:42:34 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Kevin Hilman <khilman@...aro.org>
CC:	Gleb Natapov <gleb@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	<linaro-kernel@...ts.linaro.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	"open list:KERNEL VIRTUAL MA..." <kvm@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: allow host header to be included even for
 !CONFIG_KVM

On 03/21/2013 09:27:14 AM, Kevin Hilman wrote:
> Gleb Natapov <gleb@...hat.com> writes:
> 
> > On Wed, Mar 20, 2013 at 06:58:41PM -0500, Scott Wood wrote:
> >> On 03/14/2013 07:13:46 PM, Kevin Hilman wrote:
> >> >The new context tracking subsystem unconditionally includes  
> kvm_host.h
> >> >headers for the guest enter/exit macros.  This causes a compile
> >> >failure when KVM is not enabled.
> >> >
> >> >Fix by adding an IS_ENABLED(CONFIG_KVM) check to kvm_host so it  
> can
> >> >be included/compiled even when KVM is not enabled.
> >> >
> >> >Cc: Frederic Weisbecker <fweisbec@...il.com>
> >> >Signed-off-by: Kevin Hilman <khilman@...aro.org>
> >> >---
> >> >Applies on v3.9-rc2
> >> >
> >> > include/linux/kvm_host.h | 7 ++++++-
> >> > 1 file changed, 6 insertions(+), 1 deletion(-)
> >>
> >> This broke the PPC non-KVM build, which was relying on stub
> >> functions in kvm_ppc.h, which relies on "struct vcpu" in  
> kvm_host.h.
> >>
> >> Why can't the entirety kvm_host.h be included regardless of
> >> CONFIG_KVM, just like most other feature-specific headers?  Why
> >> can't the if/else just go around the functions that you want to  
> stub
> >> out for non-KVM builds?
> >>
> > Kevin,
> >
> >  What compilation failure this patch fixes? I presume something ARM
> > related.
> 
> Not specficially ARM related, but more context tracking related since
> kernel/context_tracking.c pulls in kvm_host.h, which attempts to pull  
> in
> <asm/kvm*.h> which may not exist on some platforms.
> 
> At least for ARM, KVM support was added in v3.9 so this patch can
> probably be dropped since the non-KVM builds on ARM now work.  But any
> platform without the <asm/kvm*.h> will still be broken when trying to
> build the context tracker.

Maybe other platforms should get empty asm/kvm*.h files.  Is there  
anything from those files that the linux/kvm*.h headers need to build?

-Scott
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