From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51019) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f4zU0-0001a1-Al for qemu-devel@nongnu.org; Sat, 07 Apr 2018 21:51:05 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f4zTz-0003Wp-Eu for qemu-devel@nongnu.org; Sat, 07 Apr 2018 21:51:04 -0400 Message-ID: <5AC97568.2040502@huawei.com> Date: Sun, 8 Apr 2018 09:50:32 +0800 From: Shannon Zhao MIME-Version: 1.0 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> In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit 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: Peter Maydell Cc: qemu-arm , QEMU Developers , Eric Auger , "Dr. David Alan Gilbert" , Juan Quintela , Shannon Zhao On 2018/4/6 17:36, Peter Maydell wrote: > On 5 April 2018 at 15:22, Peter Maydell wrote: >> > 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.) > On reflection, I think I'd aim for 2.13 for this, since: > * it's not a regression > * it doesn't actually affect any of our boards, because > none of them define enough interrupt lines that they > would actually be using the top 32 that we fail to migrate > * getting the migration compat right is a bit tricky and > will benefit from having the time for careful review and testing > > Let me know if I'm wrong with any of those assumptions. Yes, it's no need to merge this for 2.12. I'll respin this patch later. Thanks, -- Shannon