From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47782) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f45mj-00027O-9o for qemu-devel@nongnu.org; Thu, 05 Apr 2018 10:22:42 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f45mi-000427-8g for qemu-devel@nongnu.org; Thu, 05 Apr 2018 10:22:41 -0400 Received: from mail-ot0-x232.google.com ([2607:f8b0:4003:c0f::232]:35852) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1f45mi-00041a-2p for qemu-devel@nongnu.org; Thu, 05 Apr 2018 10:22:40 -0400 Received: by mail-ot0-x232.google.com with SMTP id n40-v6so27353053otd.3 for ; Thu, 05 Apr 2018 07:22:40 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <1521530809-11780-1-git-send-email-zhaoshenglong@huawei.com> <1521530809-11780-3-git-send-email-zhaoshenglong@huawei.com> <5AB0F254.3050503@huawei.com> <5AB21130.2020309@huawei.com> From: Peter Maydell Date: Thu, 5 Apr 2018 15:22:12 +0100 Message-ID: Content-Type: text/plain; charset="UTF-8" Subject: Re: [Qemu-devel] [Qemu-arm] [PATCH v2 2/2] arm_gicv3_kvm: kvm_dist_get/put: skip the registers banked by GICR List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Shannon Zhao Cc: qemu-arm , QEMU Developers , Eric Auger , "Dr. David Alan Gilbert" , Juan Quintela , Shannon Zhao On 29 March 2018 at 11:54, Peter Maydell wrote: > On 23 March 2018 at 12:08, Peter Maydell wrote: >> On 21 March 2018 at 08:00, Shannon Zhao wrote: >>> On 2018/3/20 19:54, Peter Maydell wrote: >>>> Can you still successfully migrate a VM from a QEMU version >>>> without this bugfix to one with the bugfix ? >>>> >>> I've tested this case. I can migrate a VM between these two versions. >> >> Hmm. Looking at the code I can't see how that would work, >> except by accident. Let me see if I understand what's happening >> here: > I was thinking a bit more about how to handle this, and > my best idea was: > > (1) send something in the migration stream that says > "I don't have this bug" (version number change? > vmstate field that's just a "no bug" flag? subsection > with no contents?) > > (2) on the destination, if the source doesn't tell us > it doesn't have this bug, and we are running KVM, then > shift all the data in the arrays down to fix it up > [Strictly what we want to know is if the source is > running KVM, not if the destination is, but I don't > know of a way to find that out, and in practice TCG->KVM > migrations don't work anyway, so it's not a big deal.] Shannon, are you planning to look at this for 2.12, or should we postpone it to 2.13? (It's not a regression, right? So we don't necessarily have to urgently fix it for 2.12.) thanks -- PMM