From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CD3CCC83012 for ; Tue, 1 Dec 2020 12:16:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 851E72080A for ; Tue, 1 Dec 2020 12:16:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729493AbgLAMQH (ORCPT ); Tue, 1 Dec 2020 07:16:07 -0500 Received: from szxga06-in.huawei.com ([45.249.212.32]:8479 "EHLO szxga06-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726202AbgLAMQH (ORCPT ); Tue, 1 Dec 2020 07:16:07 -0500 Received: from DGGEMS407-HUB.china.huawei.com (unknown [172.30.72.59]) by szxga06-in.huawei.com (SkyGuard) with ESMTP id 4Clgyx4s0YzhlQd; Tue, 1 Dec 2020 20:15:05 +0800 (CST) Received: from [10.174.184.209] (10.174.184.209) by DGGEMS407-HUB.china.huawei.com (10.3.19.207) with Microsoft SMTP Server id 14.3.487.0; Tue, 1 Dec 2020 20:15:15 +0800 Subject: Re: [RFC PATCH v1 3/4] KVM: arm64: GICv4.1: Restore VLPI's pending state to physical side To: Marc Zyngier CC: James Morse , Julien Thierry , Suzuki K Poulose , Eric Auger , , , , , Christoffer Dall , Alex Williamson , Kirti Wankhede , Cornelia Huck , Neo Jia , , References: <20201123065410.1915-1-lushenming@huawei.com> <20201123065410.1915-4-lushenming@huawei.com> <5c724bb83730cdd5dcf7add9a812fa92@kernel.org> <2d2bcae4f871d239a1af50362f5c11a4@kernel.org> <49610291-cf57-ff78-d0ac-063af24efbb4@huawei.com> <48c10467-30f3-9b5c-bbcb-533a51516dc5@huawei.com> <2ad38077300bdcaedd2e3b073cd36743@kernel.org> <9b80d460-e149-20c8-e9b3-e695310b4ed1@huawei.com> <274dafb2e21f49326a64bb575e668793@kernel.org> From: Shenming Lu Message-ID: <59ec07e5-c017-8644-b96f-e87fe600c490@huawei.com> Date: Tue, 1 Dec 2020 20:15:14 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.2.2 MIME-Version: 1.0 In-Reply-To: <274dafb2e21f49326a64bb575e668793@kernel.org> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.184.209] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/12/1 19:50, Marc Zyngier wrote: > On 2020-12-01 11:40, Shenming Lu wrote: >> On 2020/12/1 18:55, Marc Zyngier wrote: >>> On 2020-11-30 07:23, Shenming Lu wrote: >>> >>> Hi Shenming, >>> >>>> We are pondering over this problem these days, but still don't get a >>>> good solution... >>>> Could you give us some advice on this? >>>> >>>> Or could we move the restoring of the pending states (include the sync >>>> from guest RAM and the transfer to HW) to the GIC VM state change handler, >>>> which is completely corresponding to save_pending_tables (more symmetric?) >>>> and don't expose GICv4... >>> >>> What is "the GIC VM state change handler"? Is that a QEMU thing? >> >> Yeah, it is a a QEMU thing... >> >>> We don't really have that concept in KVM, so I'd appreciate if you could >>> be a bit more explicit on this. >> >> My thought is to add a new interface (to QEMU) for the restoring of >> the pending states, which is completely corresponding to >> KVM_DEV_ARM_VGIC_SAVE_PENDING_TABLES... >> And it is called from the GIC VM state change handler in QEMU, which >> is happening after the restoring (call kvm_vgic_v4_set_forwarding()) >> but before the starting (running) of the VFIO device. > > Right, that makes sense. I still wonder how much the GIC save/restore > stuff differs from other architectures that implement similar features, > such as x86 with VT-D. I am not familiar with it... > > It is obviously too late to change the userspace interface, but I wonder > whether we missed something at the time. The interface seems to be really asymmetrical?... Or is there a possibility that we could know which irq is hw before the VFIO device calls kvm_vgic_v4_set_forwarding()? Thanks, Shenming > > Thanks, > >         M.