From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: [PATCH] i386: Decouple PAE from CONFIG_CMPXCHG64 Date: Wed, 18 Jul 2007 18:20:35 -0700 Message-ID: <469EBC63.9020803@zytor.com> References: <11847764879-git-send-email-avi@qumranet.com> <20070718181829.GA3848@one.firstfloor.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, Linus Torvalds , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Andi Kleen Return-path: In-Reply-To: <20070718181829.GA3848-qrUzlfsMFqo/4alezvVtWx2eb7JE58TQ@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.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 ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/