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=-9.0 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 02E38C433B4 for ; Fri, 7 May 2021 17:36:34 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 311AC6145E for ; Fri, 7 May 2021 17:36:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 311AC6145E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 581B34B472; Fri, 7 May 2021 13:36:32 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id TGxunBpo2MfQ; Fri, 7 May 2021 13:36:30 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id D8DFD4B4C4; Fri, 7 May 2021 13:36:30 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 178F74B472 for ; Fri, 7 May 2021 13:36:30 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id NGAvZDYVjDA0 for ; Fri, 7 May 2021 13:36:28 -0400 (EDT) Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id 6A4044B3F1 for ; Fri, 7 May 2021 13:36:28 -0400 (EDT) Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id CFD91613ED; Fri, 7 May 2021 17:36:26 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1lf4Ol-00BVKa-Qd; Fri, 07 May 2021 18:36:23 +0100 Date: Fri, 07 May 2021 18:36:23 +0100 Message-ID: <874kfepht4.wl-maz@kernel.org> From: Marc Zyngier To: Zhu Lingshan , Shaokun Zhang Subject: Re: Question on guest enable msi fail when using GICv4/4.1 In-Reply-To: <878s4qq00u.wl-maz@kernel.org> References: <3a2c66d6-6ca0-8478-d24b-61e8e3241b20@hisilicon.com> <87k0oaq5jf.wl-maz@kernel.org> <878s4qq00u.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: lingshan.zhu@intel.com, zhangshaokun@hisilicon.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, linux-pci@vger.kernel.org, alex.williamson@redhat.com, cohuck@redhat.com, tangnianyao@huawei.com, bhelgaas@google.com, eric.auger@redhat.com, jasowang@redhat.com, mst@redhat.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Cc: kvm@vger.kernel.org, "Michael S. Tsirkin" , linux-pci@vger.kernel.org, Jason Wang , Cornelia Huck , Alex Williamson , Bjorn Helgaas , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Fri, 07 May 2021 12:02:57 +0100, Marc Zyngier wrote: > > On Fri, 07 May 2021 10:58:23 +0100, > Shaokun Zhang wrote: > > > > 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. > > [+Eric, who wrote the irq_bypass infrastructure.] > > Ah, so the guest is actually paused, not in a livelock situation > (which is how I interpreted "stuck"). > > I think we should handle this case gracefully, as there should be no > expectation that the guest will be using this interrupt. Given that > VFIO seems to be pretty unfazed when a producer fails, I'm temped to > do the same thing and restart the guest. > > Also, __disconnect doesn't care about errors, so why should __connect > have this odd behaviour? > > Can you please try this? It is completely untested (and I think the > del_consumer call is odd, which is why I've also dropped it). > > Eric, what do you think? Adding Zhu, Jason, MST to the party. It all seems to be caused by this commit: commit a979a6aa009f3c99689432e0cdb5402a4463fb88 Author: Zhu Lingshan Date: Fri Jul 31 14:55:33 2020 +0800 irqbypass: do not start cons/prod when failed connect If failed to connect, there is no need to start consumer nor producer. Signed-off-by: Zhu Lingshan Suggested-by: Jason Wang Link: https://lore.kernel.org/r/20200731065533.4144-7-lingshan.zhu@intel.com Signed-off-by: Michael S. Tsirkin Zhu, I'd really like to understand why you think it is OK not to restart consumer and producers when a connection has failed to be established between the two? In the case of KVM/arm64, this results in the guest being forever suspended and never resumed. That's obviously not an acceptable regression, as there is a number of benign reasons for a connect to fail. Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm