From: "H. Peter Anvin" <hpa@zytor.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: Avi Kivity <avi@qumranet.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
kvm-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org,
caglar@pardus.org.tr
Subject: Re: [PATCH] i386: Decouple PAE from CONFIG_CMPXCHG64
Date: Wed, 18 Jul 2007 18:20:35 -0700 [thread overview]
Message-ID: <469EBC63.9020803@zytor.com> (raw)
In-Reply-To: <20070718181829.GA3848@one.firstfloor.org>
Andi Kleen wrote:
>>
>> No processors that support KVM exist that also do not support CMPXCHG64,
>> so no additional check is necessary. This setup allows for a single kernel
>> that will boot on i486 and also support KVM if available.
>
> The CONFIG should only control the early CPUID checks, which are needed for PAE
> kernels.
>
> But for something late like KVM the correct fix is really to drop
> the ifdefs around the macro and check boot_cpu_has() yourself.
>
He's checking for the appropriate functionality at runtime. What this
does is makes it impossible to select KVM when you have already selected
a CPU that doesn't support CX8.
One can, of course, question the utility, since the CPU set that
supports KVM all support CX8, but not vice versa...
-hpa
WARNING: multiple messages have this Message-ID (diff)
From: "H. Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>
To: Andi Kleen <andi-Vw/NltI1exuRpAAqCnN02g@public.gmane.org>
Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,
Linus Torvalds
<torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH] i386: Decouple PAE from CONFIG_CMPXCHG64
Date: Wed, 18 Jul 2007 18:20:35 -0700 [thread overview]
Message-ID: <469EBC63.9020803@zytor.com> (raw)
In-Reply-To: <20070718181829.GA3848-qrUzlfsMFqo/4alezvVtWx2eb7JE58TQ@public.gmane.org>
Andi Kleen wrote:
>>
>> No processors that support KVM exist that also do not support CMPXCHG64,
>> so no additional check is necessary. This setup allows for a single kernel
>> that will boot on i486 and also support KVM if available.
>
> The CONFIG should only control the early CPUID checks, which are needed for PAE
> kernels.
>
> But for something late like KVM the correct fix is really to drop
> the ifdefs around the macro and check boot_cpu_has() yourself.
>
He's checking for the appropriate functionality at runtime. What this
does is makes it impossible to select KVM when you have already selected
a CPU that doesn't support CX8.
One can, of course, question the utility, since the CPU set that
supports KVM all support CX8, but not vice versa...
-hpa
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next prev parent reply other threads:[~2007-07-19 1:22 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-07-18 16:34 [PATCH] i386: Decouple PAE from CONFIG_CMPXCHG64 Avi Kivity
2007-07-18 18:18 ` Andi Kleen
2007-07-18 18:18 ` Andi Kleen
2007-07-19 1:20 ` H. Peter Anvin [this message]
2007-07-19 1:20 ` H. Peter Anvin
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