From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1MJxB6-00053U-IZ for qemu-devel@nongnu.org; Thu, 25 Jun 2009 18:12:21 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1MJxB0-0004zf-6Q for qemu-devel@nongnu.org; Thu, 25 Jun 2009 18:12:19 -0400 Received: from [199.232.76.173] (port=57006 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MJxAz-0004zc-W4 for qemu-devel@nongnu.org; Thu, 25 Jun 2009 18:12:14 -0400 Received: from mx20.gnu.org ([199.232.41.8]:22961) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1MJxAz-0002ZO-Q1 for qemu-devel@nongnu.org; Thu, 25 Jun 2009 18:12:13 -0400 Received: from mail.codesourcery.com ([65.74.133.4]) by mx20.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1MJxAy-0005WJ-Cv for qemu-devel@nongnu.org; Thu, 25 Jun 2009 18:12:12 -0400 From: Paul Brook Subject: Re: [Qemu-devel] allow sysenter on 32bit guests running on vmx host Date: Thu, 25 Jun 2009 23:12:08 +0100 References: <20090623162140.GB4379@random.random> <200906251839.20253.paul@codesourcery.com> <20090625210249.GB12992@random.random> In-Reply-To: <20090625210249.GB12992@random.random> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200906252312.08945.paul@codesourcery.com> List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Andrea Arcangeli On Thursday 25 June 2009, Andrea Arcangeli wrote: > On Thu, Jun 25, 2009 at 06:39:19PM +0100, Paul Brook wrote: > > > What's missing is a comment saying "KVM changes this vendor id to > > > Intel when run on a VMX-capable host". > > > > I don't see how this is anything other than a KVM bug. The user requested > > an AMD vendor ID. Arbitrarily changing it to something else is just plain > > wrong. > > Oh my, no -cpu is passed on the command line, and by default the only > thing the user asks is always only one: performance. I don't buy this. I'd expect a a good proportion of users to care more about correct operation over absolute performance. A fast VM is no good if it doesn't actually work. On closer inspection I notice that we use an AMD vendor ID for the "qemu64" cpu. IMO this is wrong, we should be using our own ID. However this does not change the underlying problem - KVM absolutely should not be unilaterally changing the reported vendor ID. Maybe select a different CPU by default, and probably fail to run if the selected CPU ID is incompatible with the host hardware features, but not arbitrarily mutate the provided CPUID. Paul