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

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Date:	Sun, 24 Mar 2013 12:21:35 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Kevin Hilman <khilman@...aro.org>
Cc:	Scott Wood <scottwood@...escale.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 Thu, Mar 21, 2013 at 05:02:15PM -0700, Kevin Hilman wrote:
> Gleb Natapov <gleb@...hat.com> writes:
> 
> > On Thu, Mar 21, 2013 at 02:33:13PM -0500, Scott Wood wrote:
> >> On 03/21/2013 02:16:00 PM, Gleb Natapov wrote:
> >> >On Thu, Mar 21, 2013 at 01:42:34PM -0500, Scott Wood wrote:
> >> >> 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:
> >> >> >>> 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?
> >> >>
> >> >arch things. kvm_vcpu_arch, kvm_arch_memory_slot, kvm_arch etc.
> >> 
> >> Could define them as empty structs.
> >> 
> > Isn't is simpler for kernel/context_tracking.c to define empty
> > __guest_enter()/__guest_exit() if !CONFIG_KVM.
> 
> I proposed something like that in an earlier version but Frederic asked
> me to propose a fix to the KVM headers instead.
> 
> Just in case fixing the context tracking subsystem is preferred, 
> the patch below fixes the problem also.
> 
The patch that broke PPC build was reverted. Frederic can you get the
patch below?

> Kevin
> 
> >From f22995a262144d0d61705fa72134694d911283eb Mon Sep 17 00:00:00 2001
> From: Kevin Hilman <khilman@...aro.org>
> Date: Thu, 21 Mar 2013 16:57:14 -0700
> Subject: [PATCH] context_tracking: fix !CONFIG_KVM compile: add stub guest
>  enter/exit
> 
> When KVM is not enabled, or not available on a platform, the KVM
> headers should not be included.  Instead, just define stub
> __guest_[enter|exit] functions.
> 
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Signed-off-by: Kevin Hilman <khilman@...aro.org>
> ---
>  kernel/context_tracking.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
> index 65349f0..64b0f80 100644
> --- a/kernel/context_tracking.c
> +++ b/kernel/context_tracking.c
> @@ -15,12 +15,18 @@
>   */
>  
>  #include <linux/context_tracking.h>
> -#include <linux/kvm_host.h>
>  #include <linux/rcupdate.h>
>  #include <linux/sched.h>
>  #include <linux/hardirq.h>
>  #include <linux/export.h>
>  
> +#if IS_ENABLED(CONFIG_KVM)
> +#include <linux/kvm_host.h>
> +#else
> +#define __guest_enter()
> +#define __guest_exit()
> +#endif
> +
>  DEFINE_PER_CPU(struct context_tracking, context_tracking) = {
>  #ifdef CONFIG_CONTEXT_TRACKING_FORCE
>  	.active = true,
> -- 
> 1.8.2

--
			Gleb.
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