From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1LUSo9-0006T7-DF for qemu-devel@nongnu.org; Tue, 03 Feb 2009 16:27:49 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1LUSo7-0006S4-VY for qemu-devel@nongnu.org; Tue, 03 Feb 2009 16:27:48 -0500 Received: from [199.232.76.173] (port=38367 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1LUSo7-0006Rm-Oh for qemu-devel@nongnu.org; Tue, 03 Feb 2009 16:27:47 -0500 Received: from mx2.redhat.com ([66.187.237.31]:37491) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1LUSo5-0000mK-5A for qemu-devel@nongnu.org; Tue, 03 Feb 2009 16:27:47 -0500 Received: from int-mx2.corp.redhat.com (int-mx2.corp.redhat.com [172.16.27.26]) by mx2.redhat.com (8.13.8/8.13.8) with ESMTP id n13LReCq005350 for ; Tue, 3 Feb 2009 16:27:40 -0500 Message-ID: <4988B65B.6000308@redhat.com> Date: Tue, 03 Feb 2009 23:25:47 +0200 From: Avi Kivity MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: [PATCH 3/4] mask out forbidden cpuid features with kvm ioctl References: <1233249569-16686-1-git-send-email-glommer@redhat.com> <1233249569-16686-2-git-send-email-glommer@redhat.com> <1233249569-16686-3-git-send-email-glommer@redhat.com> <1233249569-16686-4-git-send-email-glommer@redhat.com> <498216B0.9030400@us.ibm.com> In-Reply-To: <498216B0.9030400@us.ibm.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Glauber Costa Anthony Liguori wrote: > Glauber Costa wrote: >> KVM has a (so far unused) ioctl to inform userspace >> about supported cpuid bits in the current host. >> >> The lack of this kind of checking can lead to bugs in which >> a cpuid bit is exposed but not supported by the host kernel >> (an example is fedora bug >> https://bugzilla.redhat.com/show_bug.cgi?id=481274) >> >> The current host_cpuid code is replaced by this general check. >> >> Signed-off-by: Glauber Costa >> > > So what do we do about live migration? We need a way to completely specify cpuid from the command line. The management utility would figure out what is supported (driven by both cpu capabilities and installed kvm capabilities) and fgure out a greatest common denominator, or something. > Does KVM mask a set of bits unconditionally? The kernel doesn't touch cpuid (except nx due to an historical mistake). > Before, we were masking unconditionally which should insulate > migration reasonable well. That suits migration, but not other uses of qemu. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.