From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:59505) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1R9ZrP-00043X-PI for qemu-devel@nongnu.org; Fri, 30 Sep 2011 05:58:31 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1R9ZrO-0000eE-D5 for qemu-devel@nongnu.org; Fri, 30 Sep 2011 05:58:27 -0400 Received: from ozlabs.org ([203.10.76.45]:48834) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1R9ZrO-0000e9-3s for qemu-devel@nongnu.org; Fri, 30 Sep 2011 05:58:26 -0400 Date: Fri, 30 Sep 2011 19:00:13 +1000 From: David Gibson Message-ID: <20110930090013.GI4512@yookeroo.fritz.box> References: <1317369040-30437-1-git-send-email-david@gibson.dropbear.id.au> <79DDF028-E5CE-4FBE-8EFF-FD7784A6E182@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <79DDF028-E5CE-4FBE-8EFF-FD7784A6E182@suse.de> Subject: Re: [Qemu-devel] [0/3] pseries: RFC: Advertise host CPU capabilties to guest List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexander Graf Cc: "qemu-devel@nongnu.org" On Fri, Sep 30, 2011 at 10:20:14AM +0200, Alexander Graf wrote: > > Am 30.09.2011 um 09:50 schrieb David Gibson : > > > This series contains some patches which, when using KVM, gather > > information about the capabilities of the host CPU and advertise them > > to the guest system when using the pseries machine. Specifically it > > does this for whether the CPU supports VMX, VSX and/or DFP > > instructions, and for the CPUs supported page sizes. > > > > The VSX and DFP portions of this were posted earlier, and I've fixed > > the minor comments which people made. This leaves one objection from > > Alex Graf, that whether the features are advertised should also depend > > on the target CPU selected in qemu. A similar objection may apply to > > the pagesizes patch. I guess the idea is to "clamp" the advertised > > capabilities to those permitted by the selected target CPU, but I'm > > not entirely sure what the logic here should be. > > > > Frankly, particularly in the case of KVM Book3S-HV, I'm not terribly > > convinced that attempting to make the guest CPU appear different from > > the host CPU is terribly meaningful. These patches as they stand have > > the advantage that future, roughly compatible CPUs should Just Work > > with these capabilities advertised in the correct cases. Alex, can > > you advise what sort of logic you'd like here. > > > Yes, very simple. I want you to create a CPU type 'host', similar to > how x86 does it. That should be the default CPU type for KVM with > the pseries machine. Ah, ok. I didn't realize x86 did that, but I'd been thinking something like that would make more sense. I'm away for the next week, but I'll look at this when I get the chance. > You can also add a check in-kernel that verifies if guest PVR == > host PVR for HV mode. That way you ensure that -cpu host is always > used there. If you later add compat modes, you can check them there, > but still have -cpu xxx available to tell all pieces of the kvm/qemu > chain what to use. Ok. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson