From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753535AbeCFJuP (ORCPT ); Tue, 6 Mar 2018 04:50:15 -0500 Received: from foss.arm.com ([217.140.101.70]:35584 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753316AbeCFJuL (ORCPT ); Tue, 6 Mar 2018 04:50:11 -0500 Subject: Re: [REPOST PATCH] arm/arm64: KVM: Add PSCI version selection API To: Auger Eric , Peter Maydell Cc: lkml - Kernel Mailing List , arm-mail-list , kvmarm@lists.cs.columbia.edu References: <20180215175803.6870-1-marc.zyngier@arm.com> <86o9k63f7a.wl-marc.zyngier@arm.com> <40c74835-da24-485f-14bb-a0c357c7e79b@redhat.com> From: Marc Zyngier Organization: ARM Ltd Message-ID: <81f8b489-883b-58c8-851b-c624ca72c28d@arm.com> Date: Tue, 6 Mar 2018 09:50:08 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/03/18 20:37, Auger Eric wrote: > Hi Peter, > > On 05/03/18 17:31, Peter Maydell wrote: >> On 2 March 2018 at 12:26, Auger Eric wrote: >>> Hi Marc, >>> On 02/03/18 12:11, Marc Zyngier wrote: >>>> On Fri, 02 Mar 2018 10:44:48 +0000, >>>> Auger Eric wrote: >>>>> I understand the get/set is called as part of the migration process. >>>>> So my understanding is the benefit of this series is migration fails in >>>>> those cases: >>>>> >>>>>> =0.2 source -> 0.1 destination >>>>> 0.1 source -> >=0.2 destination >>>> >>>> It also fails in the case where you migrate a 1.0 guest to something >>>> that cannot support it. >>> >>> That's because on the destination, the number of regs is less than on >>> source, right? >> >> I think it fails because the KVM_REG_ARM_PSCI_VERSION register will be >> in the migration state but not in the destination's list of registers: >> the code in QEMU's target/arm/machine.c:cpu_post_load() function that >> checks "register in their list but not ours: fail migration" will >> catch this. > > Thank you for the pointer. Yes at the time I reviewed the patch and just > focusing on the kernel code, this was not immediate to me. > >> >> That also means that we will fail migration from a new kernel where >> we've specifically asked for PSCI 0.2 to an old PSCI-0.2-only kernel >> (because the KVM_REG_ARM_PSCI_VERSION reg will appear in the migration >> stream even if its value is the one value that matches the old kernel >> behaviour). I don't know if we care about that. > > Do you know when are we likely to force PSCI 0.2 on a new kernel? At > which layer is the decision supposed to be made and on which criteria? No decent SW should need this. But if you've written a guest that cannot work if it doesn't get "2" as response to PSCI_VERSION, you can override it. M. -- Jazz is not dead. It just smells funny...