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,URIBL_BLOCKED,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 17ABEC433ED for ; Fri, 7 May 2021 09:58:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DE46B61059 for ; Fri, 7 May 2021 09:58:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234103AbhEGJ7f (ORCPT ); Fri, 7 May 2021 05:59:35 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:17474 "EHLO szxga05-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234366AbhEGJ7e (ORCPT ); Fri, 7 May 2021 05:59:34 -0400 Received: from DGGEMS401-HUB.china.huawei.com (unknown [172.30.72.59]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4Fc5Rw5QgTzkX9h; Fri, 7 May 2021 17:55:56 +0800 (CST) Received: from [10.67.77.175] (10.67.77.175) by DGGEMS401-HUB.china.huawei.com (10.3.19.201) with Microsoft SMTP Server id 14.3.498.0; Fri, 7 May 2021 17:58:23 +0800 Subject: Re: Question on guest enable msi fail when using GICv4/4.1 To: Marc Zyngier CC: , , , , Alex Williamson , Cornelia Huck , Nianyao Tang , Bjorn Helgaas References: <3a2c66d6-6ca0-8478-d24b-61e8e3241b20@hisilicon.com> <87k0oaq5jf.wl-maz@kernel.org> From: Shaokun Zhang Message-ID: Date: Fri, 7 May 2021 17:58:23 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <87k0oaq5jf.wl-maz@kernel.org> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.67.77.175] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Hi Marc, Thanks for your quick reply. On 2021/5/7 17:03, Marc Zyngier wrote: > On Fri, 07 May 2021 06:57:04 +0100, > Shaokun Zhang wrote: >> >> [This letter comes from Nianyao Tang] >> >> Hi, >> >> Using GICv4/4.1 and msi capability, guest vf driver requires 3 >> vectors and enable msi, will lead to guest stuck. > > Stuck how? Guest serial does not response anymore and guest network shutdown. > >> Qemu gets number of interrupts from Multiple Message Capable field >> set by guest. This field is aligned to a power of 2(if a function >> requires 3 vectors, it initializes it to 2). > > So I guess this is a MultiMSI device with 4 vectors, right? > Yes, it can support maximum of 32 msi interrupts, and vf driver only use 3 msi. >> However, guest driver just sends 3 mapi-cmd to vits and 3 ite >> entries is recorded in host. Vfio initializes msi interrupts using >> the number of interrupts 4 provide by qemu. When it comes to the >> 4th msi without ite in vits, in irq_bypass_register_producer, >> producer and consumer will __connect fail, due to find_ite fail, and >> do not resume guest. > > Let me rephrase this to check that I understand it: > - The device has 4 vectors > - The guest only create mappings for 3 of them > - VFIO calls kvm_vgic_v4_set_forwarding() for each vector > - KVM doesn't have a mapping for the 4th vector and returns an error > - VFIO disable this 4th vector > > Is that correct? If yes, I don't understand why that impacts the guest > at all. From what I can see, vfio_msi_set_vector_signal() just prints > a message on the console and carries on. > function calls: --> vfio_msi_set_vector_signal --> irq_bypass_register_producer -->__connect in __connect, add_producer finally calls kvm_vgic_v4_set_forwarding and fails to get the 4th mapping. When add_producer fail, it does not call cons->start, calls kvm_arch_irq_bypass_start and then kvm_arm_resume_guest. Thanks, Shaokun >> Do we support this case, Guest function using msi interrupts number >> not aligned to a power of 2? Or qemu should provide correct msi >> interrupts number? > > QEMU cannot know how many vectors are in use, and the guest is free to > issue mappings for the exact number of vectors it wants to service. > > Please describe what breaks the guest here. > > Thanks, > > M. >