linux-kernel - Re: [tip:x86/urgent] x86/kconfig: Add a Kconfig shortcut for building working KVM guest kernels

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Message-ID: <alpine.DEB.2.02.1305011503200.3267@chino.kir.corp.google.com>
Date:	Wed, 1 May 2013 15:09:13 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Borislav Petkov <bp@...en8.de>
cc:	Ingo Molnar <mingo@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org, Pekka Enberg <penberg@...nel.org>,
	levinsasha928@...il.com, mtosatti@...hat.com, tglx@...utronix.de,
	Borislav Petkov <bp@...e.de>, fengguang.wu@...el.com,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/urgent] x86/kconfig:  Add a Kconfig shortcut for building
 working KVM guest kernels

On Wed, 1 May 2013, Borislav Petkov wrote:

> $ make allnoconfig
>   HOSTCC  scripts/basic/fixdep
>   SHIPPED scripts/kconfig/zconf.tab.c
>   SHIPPED scripts/kconfig/zconf.lex.c
>   HOSTCC  scripts/kconfig/conf.o
>   SHIPPED scripts/kconfig/zconf.hash.c
>   HOSTCC  scripts/kconfig/zconf.tab.o
>   HOSTLD  scripts/kconfig/conf
> scripts/kconfig/conf --allnoconfig Kconfig
> #
> # configuration written to .config
> #
> $ make menuconfig				<--- select the options you mention above

menuconfig is going to give you defaults that the newly-enabled options 
allow to be configured without you knowing.  It's better to just flip 
these options my hand and use make oldconfig (or yes "n" | make 
oldconfig) to disable everything else that is now configurable.

This is done because we're addressing unmet dependency problems, so we'll 
want to disable as much as allowed.  Those dependencies are usually signs 
of real build errors (as they were for the PCI problem) since we're 
enabling options that don't have their prerequisites.

Unfortunately, the way you're implementing KVM_GUEST_COMMON_OPTIONS will 
typically result in this if the options you "select" get new dependencies 
in the future.  So you'll always be updating this option constantly with 
these types of problems.

I've attached the config that emits both these warnings (copy it as 
.config and use make oldconfig) on top of today's linux-next and your 
suggested patch.

The errors are rather straightforward, though: we aren't depending or 
selecting on CONFIG_NET_CORE and ARCH_SUPPORTS_MSI.
View attachment "config" of type "TEXT/PLAIN" (38418 bytes)