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

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Message-ID: <87ppyshlq5.fsf@linaro.org>
Date:	Thu, 21 Mar 2013 07:27:14 -0700
From:	Kevin Hilman <khilman@...aro.org>
To:	Gleb Natapov <gleb@...hat.com>
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

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.

Kevin
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