From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42552) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eyYgp-0002Ve-7H for qemu-devel@nongnu.org; Wed, 21 Mar 2018 04:01:47 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eyYgj-0006o3-Lg for qemu-devel@nongnu.org; Wed, 21 Mar 2018 04:01:43 -0400 Message-ID: <5AB21130.2020309@huawei.com> Date: Wed, 21 Mar 2018 16:00:48 +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> 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 On 2018/3/20 19:54, Peter Maydell wrote: > On 20 March 2018 at 11:36, Shannon Zhao wrote: >> >> >> On 2018/3/20 19:22, Peter Maydell wrote: >>> On 20 March 2018 at 07:26, Shannon Zhao wrote: >>>> While we skip the GIC_INTERNAL irqs, we don't change the register offset >>>> accordingly. This will overlap the GICR registers value and leave the >>>> last GIC_INTERNAL irq's registers out of update. >>>> >>>> Fix this by skipping the registers banked by GICR. >>>> >>> >>> I'm still not entirely sure what the underlying problem >>> you're trying to fix is... >>> >>> Do we fail to correctly migrate a VM without this change? >>> Does the code work on some host CPU/GIC implementations but >>> not others? Is this just improving efficiency by avoiding >>> doing some unnecessary work? >>> >> When we reboot a VM and before entering uefi or guest kernel, we expect >> all these registers staying at the initial state. But currently these >> registers of the last 32 irqs are not reset. For example, the PRIORITY >> of irq from 32 to 255 is 0 but the PRIORITY of irq from 256 to 287 is >> 0xa0(Linux kernel set the PRIORITY to 0xa0 by default). >> >> When migrating a VM, since we don't save and restore the registers of >> the last 32 irq, so the PRIORITY is 0 while we expecting 0xa0. >> And also it will overlap the PRIORITY of SGIs and PPIs. >> >> We don't fail to migrate a vm since currently we don't use the last 32 >> irqs in virt machine. But the bug is still there. > > Oh, I see, the number of registers we transfer is accounting > for the first N registers in the bank not being used, but the > first register offset to transfer wasn't. > > 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. Thanks, -- Shannon