From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoffer Dall Subject: Re: [PATCH] arm64/kvm: Add generic v8 KVM target Date: Tue, 23 Jun 2015 14:39:59 +0200 Message-ID: <20150623123959.GF4035@cbox> References: <1434531646-4873-1-git-send-email-suzuki.poulose@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 497ED564EF for ; Tue, 23 Jun 2015 08:29:10 -0400 (EDT) Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 00hA31hpZZ32 for ; Tue, 23 Jun 2015 08:29:08 -0400 (EDT) Received: from mail-lb0-f172.google.com (mail-lb0-f172.google.com [209.85.217.172]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id 45AC2564E6 for ; Tue, 23 Jun 2015 08:29:07 -0400 (EDT) Received: by lbbvz5 with SMTP id vz5so5796030lbb.0 for ; Tue, 23 Jun 2015 05:40:00 -0700 (PDT) Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu To: Peter Maydell Cc: kvm-devel , Marc Zyngier , timur@codeaurora.org, vgandhi@codeaurora.org, "kvmarm@lists.cs.columbia.edu" , arm-mail-list List-Id: kvmarm@lists.cs.columbia.edu On Mon, Jun 22, 2015 at 09:44:48AM +0100, Peter Maydell wrote: > On 17 June 2015 at 10:00, Suzuki K. Poulose wrote: > > From: "Suzuki K. Poulose" > > > > This patch adds a generic ARM v8 KVM target cpu type for use > > by the new CPUs which eventualy ends up using the common sys_reg > > table. For backward compatibility the existing targets have been > > preserved. Any new target CPU that can be covered by generic v8 > > sys_reg tables should make use of the new generic target. > > How do you intend this to work for cross-host migration? > Is the idea that the kernel guarantees that "generic" looks > 100% the same to the guest regardless of host hardware? I'm > not sure that can be made to work, given impdef differences > in ID register values, bp/wp registers, and so on. > > Given that, it seems to me that we still need to provide > KVM_ARM_TARGET_$THISCPU defines so userspace can request > a specific guest CPU flavour; so what does this patch > provide that isn't already provided by just having userspace > query for the "preferred" CPU type as it does already? > I'm guessing the intention is to avoid having to add code in the kernel to support KVM on a new CPU where nothing else needs to be done to support KVM on that system. Wrt. migration, I was also wondering about this. Would the differences in the CPU architecture be detected when feeding back the invariant sysregs from userspace on VM restore? -Christoffer