From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52366) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gZjez-00075s-8S for qemu-devel@nongnu.org; Wed, 19 Dec 2018 16:45:45 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gZjey-0002wJ-BF for qemu-devel@nongnu.org; Wed, 19 Dec 2018 16:45:45 -0500 Received: from mail-wr1-x441.google.com ([2a00:1450:4864:20::441]:41000) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1gZjey-0002vV-4T for qemu-devel@nongnu.org; Wed, 19 Dec 2018 16:45:44 -0500 Received: by mail-wr1-x441.google.com with SMTP id x10so21023085wrs.8 for ; Wed, 19 Dec 2018 13:45:43 -0800 (PST) Sender: Paolo Bonzini References: <20181219085038.7729-1-peterx@redhat.com> <20181219085038.7729-3-peterx@redhat.com> <20181219212418.GJ19442@habkost.net> From: Paolo Bonzini Message-ID: <2b60279a-26bc-1569-3f3c-da507fed2c44@redhat.com> Date: Wed, 19 Dec 2018 22:45:40 +0100 MIME-Version: 1.0 In-Reply-To: <20181219212418.GJ19442@habkost.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 2/4] q35: set split kernel irqchip as default List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eduardo Habkost Cc: Peter Xu , qemu-devel@nongnu.org, "Michael S . Tsirkin" , Igor Mammedov , libvir-list@redhat.com, "Daniel P. Berrange" , Jiri Denemark On 19/12/18 22:24, Eduardo Habkost wrote: > On Wed, Dec 19, 2018 at 09:12:55PM +0100, Paolo Bonzini wrote: >> On 19/12/18 09:50, Peter Xu wrote: >>> Starting from QEMU 4.0, let's specify "split" as the default value for >>> kernel-irqchip. >>> >>> So for QEMU>=4.0 we'll have: allowed=Y,required=N,split=Y >>> for QEMU<=3.1 we'll have: allowed=Y,required=N,split=N >>> (omitting all the "kernel_irqchip_" prefix) >>> >>> Note that this "split" is optional - we'll first try to enable split >>> kernel irqchip, and we'll fall back to complete kernel irqchip if we >>> found that the kernel capability is missing. >> >> Please just fail completely and require a new kernel for the 4.0 machine >> type. There are subtle differences between kernel and QEMU irqchip, I >> don't think we want to open that can of worms. > > This would make existing VMs that are runnable with pc-q35-3.1.0 > not runnable by only updating the machine-type. > > The good news is that we can make this a non-issue by clearly > documenting that QEMU needs a more recent kernel (just like we'll > do for RDTSCP[1]). Right, RDTSCP is exactly what came to mind. Paolo