linux-kernel - Re: [PATCH] x86: don't allow KVM_CLOCK without HAVE

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Date:	Mon, 17 Mar 2008 08:55:55 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Avi Kivity <avi@...ranet.com>
Cc:	lkml <linux-kernel@...r.kernel.org>, linux-next@...r.kernel.org,
	kvm-devel@...ts.sourceforge.net, tglx <tglx@...utronix.de>,
	mingo <mingo@...hat.com>, hpa <hpa@...or.com>
Subject: Re: [PATCH] x86: don't allow KVM_CLOCK without HAVE_KVM

On Sun, 16 Mar 2008 13:13:08 +0200 Avi Kivity wrote:

> Randy Dunlap wrote:
> > From: Randy Dunlap <randy.dunlap@...cle.com>
> >
> > Make KVM_CLOCK depend on HAVE_KVM.  Otherwise a Voyager build can
> > fail with:
> >
> >   CC      arch/x86/kernel/asm-offsets.s
> > In file included from include2/asm/irqflags.h:59,
> >                  from /local/linsrc/next-20080314/include/linux/irqflags.h:46,
> >                  from include2/asm/system.h:11,
> >                  from include2/asm/processor.h:21,
> >                  from include2/asm/atomic_32.h:5,
> >                  from include2/asm/atomic.h:2,
> >                  from /local/linsrc/next-20080314/include/linux/crypto.h:20,
> >                  from /local/linsrc/next-20080314/arch/x86/kernel/asm-offsets_32.c:7,
> >                  from /local/linsrc/next-20080314/arch/x86/kernel/asm-offsets.c:2:
> > include2/asm/paravirt.h: In function 'startup_ipi_hook':
> > include2/asm/paravirt.h:856: error: 'struct pv_apic_ops' has no member named 'startup_ipi_hook'
> > include2/asm/paravirt.h:856: error: 'struct pv_apic_ops' has no member named 'startup_ipi_hook'
> > include2/asm/paravirt.h:856: error: memory input 4 is not directly addressable
> > make[2]: *** [arch/x86/kernel/asm-offsets.s] Error 1
> > make[1]: *** [prepare0] Error 2
> > make: *** [sub-make] Error 2
> >
> >   
> 
> Looks like it's a general paravirt vs voyager issue, nothing kvmclock 
> specific about it.  Wouldn't it be better to have voyager and paravirt 
> mutually exclude each other, rather than every paravirt user?

They do generally mutually exclude each other.  I think that the problem
is just that dirty old "select PARAVIRT" in config KVM_CLOCK.
PARAVIRT depends on !(X86_VISWS || X86_VOYAGER), but "select" doesn't
care^W honor that.  As Documentation/kbuild/kconfig-language.txt says:

	"In general use select only for
	non-visible symbols (no prompts anywhere) and for symbols with
	no dependencies. That will limit the usefulness but on the
	other hand avoid the illegal configurations all over. kconfig
	should one day warn about such things."

so changing the select to depends on would fix it, but that's the
only fix that I know of.

> HAVE_KVM is intended for the host, not the guest, btw.


---
~Randy
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