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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6667FC433FE for ; Thu, 2 Dec 2021 10:21:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1356929AbhLBKYm (ORCPT ); Thu, 2 Dec 2021 05:24:42 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:43415 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1356915AbhLBKYl (ORCPT ); Thu, 2 Dec 2021 05:24:41 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1638440478; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=m4HlULEGQ+u/lfRbooSYsdnXMPgjmp3tTKFINSv7JFM=; b=jR2Jxz3tP2VpsAq9tl8h1fuMHXT3d4aRFjfL2YL8Yp8+fL9yNCSBCk2M2XUVxcPZUeImuj Kdztr1P5c1mfOqvLncQKKkERVbc4JwxdRYYZKRA8+2cy8p0EZ7gYyahQPUAijxFYxvXy/3 cWsYE8UIY7EEbOF2kmPSSiMoXuB1Aig= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-590-FTxu8o4JPGuzaC45aDiDWA-1; Thu, 02 Dec 2021 05:21:13 -0500 X-MC-Unique: FTxu8o4JPGuzaC45aDiDWA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id ABDFE81EE60; Thu, 2 Dec 2021 10:21:09 +0000 (UTC) Received: from starship (unknown [10.40.192.24]) by smtp.corp.redhat.com (Postfix) with ESMTP id D73445D9CA; Thu, 2 Dec 2021 10:20:56 +0000 (UTC) Message-ID: Subject: Re: [PATCH v2 11/43] KVM: Don't block+unblock when halt-polling is successful From: Maxim Levitsky To: Sean Christopherson Cc: Marc Zyngier , Huacai Chen , Aleksandar Markovic , Paul Mackerras , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Paolo Bonzini , James Morse , Alexandru Elisei , Suzuki K Poulose , Atish Patra , David Hildenbrand , Cornelia Huck , Claudio Imbrenda , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, David Matlack , Oliver Upton , Jing Zhang Date: Thu, 02 Dec 2021 12:20:55 +0200 In-Reply-To: References: <20211009021236.4122790-1-seanjc@google.com> <20211009021236.4122790-12-seanjc@google.com> <4e883728e3e5201a94eb46b56315afca5e95ad9c.camel@redhat.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.5 (3.36.5-2.fc32) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2021-11-29 at 17:25 +0000, Sean Christopherson wrote: > On Mon, Nov 29, 2021, Maxim Levitsky wrote: > > (This thing is that when you tell the IOMMU that a vCPU is not running, > > Another thing I discovered that this patch series totally breaks my VMs, > > without cpu_pm=on The whole series (I didn't yet bisect it) makes even my > > fedora32 VM be very laggy, almost unusable, and it only has one > > passed-through device, a nic). > > Grrrr, the complete lack of comments in the KVM code and the separate paths for > VMX vs SVM when handling HLT with APICv make this all way for difficult to > understand than it should be. > > The hangs are likely due to: > > KVM: SVM: Unconditionally mark AVIC as running on vCPU load (with APICv) > > If a posted interrupt arrives after KVM has done its final search through the vIRR, > but before avic_update_iommu_vcpu_affinity() is called, the posted interrupt will > be set in the vIRR without triggering a host IRQ to wake the vCPU via the GA log. > > I.e. KVM is missing an equivalent to VMX's posted interrupt check for an outstanding > notification after switching to the wakeup vector. > > For now, the least awful approach is sadly to keep the vcpu_(un)blocking() hooks. > Unlike VMX's PI support, there's no fast check for an interrupt being posted (KVM > would have to rewalk the vIRR), no easy to signal the current CPU to do wakeup (I > don't think KVM even has access to the IRQ used by the owning IOMMU), and there's > no simplification of load/put code. I have an idea. Why do we even use/need the GA log? Why not, just disable the 'guest mode' in the iommu and let it sent good old normal interrupt when a vCPU is not running, just like we do when we inhibit the AVIC? GA log makes all devices that share an iommu (there are 4 iommus per package these days, some without useful devices) go through a single (!) msi like interrupt, which is even for some reason implemented by a threaded IRQ in the linux kernel. Best regards, Maxim Levitsky > > If the scheduler were changed to support waking in the sched_out path, then I'd be > more inclined to handle this in avic_vcpu_put() by rewalking the vIRR one final > time, but for now it's not worth it. > > > If I apply though only the patch series up to this patch, my fedora VM seems > > to work fine, but my windows VM still locks up hard when I run 'LatencyTop' > > in it, which doesn't happen without this patch. > > Buy "run 'LatencyTop' in it", do you mean running something in the Windows guest? > The only search results I can find for LatencyTop are Linux specific. > > > So far the symptoms I see is that on VCPU 0, ISR has quite high interrupt > > (0xe1 last time I seen it), TPR and PPR are 0xe0 (although I have seen TPR to > > have different values), and IRR has plenty of interrupts with lower priority. > > The VM seems to be stuck in this case. As if its EOI got lost or something is > > preventing the IRQ handler from issuing EOI. > > > > LatencyTop does install some form of a kernel driver which likely does meddle > > with interrupts (maybe it sends lots of self IPIs?). > > > > 100% reproducible as soon as I start monitoring with LatencyTop. > > > > Without this patch it works (or if disabling halt polling), > > Huh. I assume everything works if you disable halt polling _without_ this patch > applied? > > If so, that implies that successful halt polling without mucking with vCPU IOMMU > affinity is somehow problematic. I can't think of any relevant side effects other > than timing. > 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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 166C0C433F5 for ; Thu, 2 Dec 2021 10:21:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Date:Cc:To:From:Subject:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=+658xaNB9uH/wwXXhCitkhGjgEEwL6/JHtiog/EtQVE=; b=oidIJvHGLtm8gn a9usLYLg/kJUQoDSROQh0hzUJo+nM17DQDnBpqAgHjo3zZXIsPo/fbpqMVDRENYgwEIIBnbJfDv9+ jHLBjtg79l8YC3kQGrRR9oKrVkDlU+CGzt1bQMWSF8AvSkFh2t1dVeXyJZoITr/j7SA9Ulgoj9fD8 3+dGk8xePCQCUcEJotY0MJaWeHJXyEOeNdOHTc/BkRs2vA6Byx/D5JR2p/udxigOevTGnlXOjOdlA VL690rbCXPCsy6fk0Pv0xTFArszE0zmZDtidb5lafuIUYN2n2bM1CtCywe1/CrvxI/yGuaimHxuwP UbeHOSUlSyCVZ2sngcEg==; 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Thu, 02 Dec 2021 05:21:13 -0500 X-MC-Unique: FTxu8o4JPGuzaC45aDiDWA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id ABDFE81EE60; Thu, 2 Dec 2021 10:21:09 +0000 (UTC) Received: from starship (unknown [10.40.192.24]) by smtp.corp.redhat.com (Postfix) with ESMTP id D73445D9CA; Thu, 2 Dec 2021 10:20:56 +0000 (UTC) Message-ID: Subject: Re: [PATCH v2 11/43] KVM: Don't block+unblock when halt-polling is successful From: Maxim Levitsky To: Sean Christopherson Cc: Marc Zyngier , Huacai Chen , Aleksandar Markovic , Paul Mackerras , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Paolo Bonzini , James Morse , Alexandru Elisei , Suzuki K Poulose , Atish Patra , David Hildenbrand , Cornelia Huck , Claudio Imbrenda , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, David Matlack , Oliver Upton , Jing Zhang Date: Thu, 02 Dec 2021 12:20:55 +0200 In-Reply-To: References: <20211009021236.4122790-1-seanjc@google.com> <20211009021236.4122790-12-seanjc@google.com> <4e883728e3e5201a94eb46b56315afca5e95ad9c.camel@redhat.com> User-Agent: Evolution 3.36.5 (3.36.5-2.fc32) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211202_022118_305416_A93D0AE1 X-CRM114-Status: GOOD ( 36.16 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On Mon, 2021-11-29 at 17:25 +0000, Sean Christopherson wrote: > On Mon, Nov 29, 2021, Maxim Levitsky wrote: > > (This thing is that when you tell the IOMMU that a vCPU is not running, > > Another thing I discovered that this patch series totally breaks my VMs, > > without cpu_pm=on The whole series (I didn't yet bisect it) makes even my > > fedora32 VM be very laggy, almost unusable, and it only has one > > passed-through device, a nic). > > Grrrr, the complete lack of comments in the KVM code and the separate paths for > VMX vs SVM when handling HLT with APICv make this all way for difficult to > understand than it should be. > > The hangs are likely due to: > > KVM: SVM: Unconditionally mark AVIC as running on vCPU load (with APICv) > > If a posted interrupt arrives after KVM has done its final search through the vIRR, > but before avic_update_iommu_vcpu_affinity() is called, the posted interrupt will > be set in the vIRR without triggering a host IRQ to wake the vCPU via the GA log. > > I.e. KVM is missing an equivalent to VMX's posted interrupt check for an outstanding > notification after switching to the wakeup vector. > > For now, the least awful approach is sadly to keep the vcpu_(un)blocking() hooks. > Unlike VMX's PI support, there's no fast check for an interrupt being posted (KVM > would have to rewalk the vIRR), no easy to signal the current CPU to do wakeup (I > don't think KVM even has access to the IRQ used by the owning IOMMU), and there's > no simplification of load/put code. I have an idea. Why do we even use/need the GA log? Why not, just disable the 'guest mode' in the iommu and let it sent good old normal interrupt when a vCPU is not running, just like we do when we inhibit the AVIC? GA log makes all devices that share an iommu (there are 4 iommus per package these days, some without useful devices) go through a single (!) msi like interrupt, which is even for some reason implemented by a threaded IRQ in the linux kernel. Best regards, Maxim Levitsky > > If the scheduler were changed to support waking in the sched_out path, then I'd be > more inclined to handle this in avic_vcpu_put() by rewalking the vIRR one final > time, but for now it's not worth it. > > > If I apply though only the patch series up to this patch, my fedora VM seems > > to work fine, but my windows VM still locks up hard when I run 'LatencyTop' > > in it, which doesn't happen without this patch. > > Buy "run 'LatencyTop' in it", do you mean running something in the Windows guest? > The only search results I can find for LatencyTop are Linux specific. > > > So far the symptoms I see is that on VCPU 0, ISR has quite high interrupt > > (0xe1 last time I seen it), TPR and PPR are 0xe0 (although I have seen TPR to > > have different values), and IRR has plenty of interrupts with lower priority. > > The VM seems to be stuck in this case. As if its EOI got lost or something is > > preventing the IRQ handler from issuing EOI. > > > > LatencyTop does install some form of a kernel driver which likely does meddle > > with interrupts (maybe it sends lots of self IPIs?). > > > > 100% reproducible as soon as I start monitoring with LatencyTop. > > > > Without this patch it works (or if disabling halt polling), > > Huh. I assume everything works if you disable halt polling _without_ this patch > applied? > > If so, that implies that successful halt polling without mucking with vCPU IOMMU > affinity is somehow problematic. I can't think of any relevant side effects other > than timing. > _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv 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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id F41E4C433F5 for ; Thu, 2 Dec 2021 10:22:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Date:Cc:To:From:Subject:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, 2021-11-29 at 17:25 +0000, Sean Christopherson wrote: > On Mon, Nov 29, 2021, Maxim Levitsky wrote: > > (This thing is that when you tell the IOMMU that a vCPU is not running, > > Another thing I discovered that this patch series totally breaks my VMs, > > without cpu_pm=on The whole series (I didn't yet bisect it) makes even my > > fedora32 VM be very laggy, almost unusable, and it only has one > > passed-through device, a nic). > > Grrrr, the complete lack of comments in the KVM code and the separate paths for > VMX vs SVM when handling HLT with APICv make this all way for difficult to > understand than it should be. > > The hangs are likely due to: > > KVM: SVM: Unconditionally mark AVIC as running on vCPU load (with APICv) > > If a posted interrupt arrives after KVM has done its final search through the vIRR, > but before avic_update_iommu_vcpu_affinity() is called, the posted interrupt will > be set in the vIRR without triggering a host IRQ to wake the vCPU via the GA log. > > I.e. KVM is missing an equivalent to VMX's posted interrupt check for an outstanding > notification after switching to the wakeup vector. > > For now, the least awful approach is sadly to keep the vcpu_(un)blocking() hooks. > Unlike VMX's PI support, there's no fast check for an interrupt being posted (KVM > would have to rewalk the vIRR), no easy to signal the current CPU to do wakeup (I > don't think KVM even has access to the IRQ used by the owning IOMMU), and there's > no simplification of load/put code. I have an idea. Why do we even use/need the GA log? Why not, just disable the 'guest mode' in the iommu and let it sent good old normal interrupt when a vCPU is not running, just like we do when we inhibit the AVIC? GA log makes all devices that share an iommu (there are 4 iommus per package these days, some without useful devices) go through a single (!) msi like interrupt, which is even for some reason implemented by a threaded IRQ in the linux kernel. Best regards, Maxim Levitsky > > If the scheduler were changed to support waking in the sched_out path, then I'd be > more inclined to handle this in avic_vcpu_put() by rewalking the vIRR one final > time, but for now it's not worth it. > > > If I apply though only the patch series up to this patch, my fedora VM seems > > to work fine, but my windows VM still locks up hard when I run 'LatencyTop' > > in it, which doesn't happen without this patch. > > Buy "run 'LatencyTop' in it", do you mean running something in the Windows guest? > The only search results I can find for LatencyTop are Linux specific. > > > So far the symptoms I see is that on VCPU 0, ISR has quite high interrupt > > (0xe1 last time I seen it), TPR and PPR are 0xe0 (although I have seen TPR to > > have different values), and IRR has plenty of interrupts with lower priority. > > The VM seems to be stuck in this case. As if its EOI got lost or something is > > preventing the IRQ handler from issuing EOI. > > > > LatencyTop does install some form of a kernel driver which likely does meddle > > with interrupts (maybe it sends lots of self IPIs?). > > > > 100% reproducible as soon as I start monitoring with LatencyTop. > > > > Without this patch it works (or if disabling halt polling), > > Huh. I assume everything works if you disable halt polling _without_ this patch > applied? > > If so, that implies that successful halt polling without mucking with vCPU IOMMU > affinity is somehow problematic. I can't think of any relevant side effects other > than timing. > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel 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 Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by smtp.lore.kernel.org (Postfix) with ESMTP id 84E1AC433F5 for ; Fri, 3 Dec 2021 13:46:45 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id E61694B1B4; Fri, 3 Dec 2021 08:46:44 -0500 (EST) X-Virus-Scanned: at lists.cs.columbia.edu Authentication-Results: mm01.cs.columbia.edu (amavisd-new); dkim=softfail (fail, message has been altered) header.i=@redhat.com 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 6ixun9fU2PDD; Fri, 3 Dec 2021 08:46:43 -0500 (EST) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id F25B44B17C; Fri, 3 Dec 2021 08:46:42 -0500 (EST) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 000F44B162 for ; Thu, 2 Dec 2021 05:21:18 -0500 (EST) 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 C9tVfnJkL8gy for ; Thu, 2 Dec 2021 05:21:17 -0500 (EST) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 374C24B15A for ; Thu, 2 Dec 2021 05:21:17 -0500 (EST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1638440476; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=m4HlULEGQ+u/lfRbooSYsdnXMPgjmp3tTKFINSv7JFM=; b=ZLORlFq2dx8J/AbUjS+HqDMeRwbXOS+3jZv9Xbb9NxXuexafY5zboJHqPUIPcne0F96r/t +PJ5bwSeuKmRXxRhmm+Mq05xXmnaMFreC8Y8Hh0VLACM5s4HLN/mV3KpVDQn0yz1309B/1 tjw/iJLkX3DqhaJbricMKefBI86TJJ0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-590-FTxu8o4JPGuzaC45aDiDWA-1; Thu, 02 Dec 2021 05:21:13 -0500 X-MC-Unique: FTxu8o4JPGuzaC45aDiDWA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id ABDFE81EE60; Thu, 2 Dec 2021 10:21:09 +0000 (UTC) Received: from starship (unknown [10.40.192.24]) by smtp.corp.redhat.com (Postfix) with ESMTP id D73445D9CA; Thu, 2 Dec 2021 10:20:56 +0000 (UTC) Message-ID: Subject: Re: [PATCH v2 11/43] KVM: Don't block+unblock when halt-polling is successful From: Maxim Levitsky To: Sean Christopherson Date: Thu, 02 Dec 2021 12:20:55 +0200 In-Reply-To: References: <20211009021236.4122790-1-seanjc@google.com> <20211009021236.4122790-12-seanjc@google.com> <4e883728e3e5201a94eb46b56315afca5e95ad9c.camel@redhat.com> User-Agent: Evolution 3.36.5 (3.36.5-2.fc32) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mailman-Approved-At: Fri, 03 Dec 2021 08:46:41 -0500 Cc: Cornelia Huck , Wanpeng Li , kvm@vger.kernel.org, David Hildenbrand , linux-kernel@vger.kernel.org, Paul Mackerras , Atish Patra , linux-riscv@lists.infradead.org, Claudio Imbrenda , kvmarm@lists.cs.columbia.edu, Janosch Frank , Marc Zyngier , Joerg Roedel , Huacai Chen , Christian Borntraeger , Aleksandar Markovic , Albert Ou , kvm-ppc@vger.kernel.org, Paul Walmsley , David Matlack , linux-arm-kernel@lists.infradead.org, Jim Mattson , Anup Patel , linux-mips@vger.kernel.org, Palmer Dabbelt , kvm-riscv@lists.infradead.org, Paolo Bonzini , Vitaly Kuznetsov 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 Mon, 2021-11-29 at 17:25 +0000, Sean Christopherson wrote: > On Mon, Nov 29, 2021, Maxim Levitsky wrote: > > (This thing is that when you tell the IOMMU that a vCPU is not running, > > Another thing I discovered that this patch series totally breaks my VMs, > > without cpu_pm=on The whole series (I didn't yet bisect it) makes even my > > fedora32 VM be very laggy, almost unusable, and it only has one > > passed-through device, a nic). > > Grrrr, the complete lack of comments in the KVM code and the separate paths for > VMX vs SVM when handling HLT with APICv make this all way for difficult to > understand than it should be. > > The hangs are likely due to: > > KVM: SVM: Unconditionally mark AVIC as running on vCPU load (with APICv) > > If a posted interrupt arrives after KVM has done its final search through the vIRR, > but before avic_update_iommu_vcpu_affinity() is called, the posted interrupt will > be set in the vIRR without triggering a host IRQ to wake the vCPU via the GA log. > > I.e. KVM is missing an equivalent to VMX's posted interrupt check for an outstanding > notification after switching to the wakeup vector. > > For now, the least awful approach is sadly to keep the vcpu_(un)blocking() hooks. > Unlike VMX's PI support, there's no fast check for an interrupt being posted (KVM > would have to rewalk the vIRR), no easy to signal the current CPU to do wakeup (I > don't think KVM even has access to the IRQ used by the owning IOMMU), and there's > no simplification of load/put code. I have an idea. Why do we even use/need the GA log? Why not, just disable the 'guest mode' in the iommu and let it sent good old normal interrupt when a vCPU is not running, just like we do when we inhibit the AVIC? GA log makes all devices that share an iommu (there are 4 iommus per package these days, some without useful devices) go through a single (!) msi like interrupt, which is even for some reason implemented by a threaded IRQ in the linux kernel. Best regards, Maxim Levitsky > > If the scheduler were changed to support waking in the sched_out path, then I'd be > more inclined to handle this in avic_vcpu_put() by rewalking the vIRR one final > time, but for now it's not worth it. > > > If I apply though only the patch series up to this patch, my fedora VM seems > > to work fine, but my windows VM still locks up hard when I run 'LatencyTop' > > in it, which doesn't happen without this patch. > > Buy "run 'LatencyTop' in it", do you mean running something in the Windows guest? > The only search results I can find for LatencyTop are Linux specific. > > > So far the symptoms I see is that on VCPU 0, ISR has quite high interrupt > > (0xe1 last time I seen it), TPR and PPR are 0xe0 (although I have seen TPR to > > have different values), and IRR has plenty of interrupts with lower priority. > > The VM seems to be stuck in this case. As if its EOI got lost or something is > > preventing the IRQ handler from issuing EOI. > > > > LatencyTop does install some form of a kernel driver which likely does meddle > > with interrupts (maybe it sends lots of self IPIs?). > > > > 100% reproducible as soon as I start monitoring with LatencyTop. > > > > Without this patch it works (or if disabling halt polling), > > Huh. I assume everything works if you disable halt polling _without_ this patch > applied? > > If so, that implies that successful halt polling without mucking with vCPU IOMMU > affinity is somehow problematic. I can't think of any relevant side effects other > than timing. > _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm From mboxrd@z Thu Jan 1 00:00:00 1970 From: Maxim Levitsky Date: Thu, 02 Dec 2021 10:20:55 +0000 Subject: Re: [PATCH v2 11/43] KVM: Don't block+unblock when halt-polling is successful Message-Id: List-Id: References: <20211009021236.4122790-1-seanjc@google.com> <20211009021236.4122790-12-seanjc@google.com> <4e883728e3e5201a94eb46b56315afca5e95ad9c.camel@redhat.com> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Sean Christopherson Cc: Marc Zyngier , Huacai Chen , Aleksandar Markovic , Paul Mackerras , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Paolo Bonzini , James Morse , Alexandru Elisei , Suzuki K Poulose , Atish Patra , David Hildenbrand , Cornelia Huck , Claudio Imbrenda , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, David Matlack , Oliver Upton , Jing Zhang On Mon, 2021-11-29 at 17:25 +0000, Sean Christopherson wrote: > On Mon, Nov 29, 2021, Maxim Levitsky wrote: > > (This thing is that when you tell the IOMMU that a vCPU is not running, > > Another thing I discovered that this patch series totally breaks my VMs, > > without cpu_pm=on The whole series (I didn't yet bisect it) makes even my > > fedora32 VM be very laggy, almost unusable, and it only has one > > passed-through device, a nic). > > Grrrr, the complete lack of comments in the KVM code and the separate paths for > VMX vs SVM when handling HLT with APICv make this all way for difficult to > understand than it should be. > > The hangs are likely due to: > > KVM: SVM: Unconditionally mark AVIC as running on vCPU load (with APICv) > > If a posted interrupt arrives after KVM has done its final search through the vIRR, > but before avic_update_iommu_vcpu_affinity() is called, the posted interrupt will > be set in the vIRR without triggering a host IRQ to wake the vCPU via the GA log. > > I.e. KVM is missing an equivalent to VMX's posted interrupt check for an outstanding > notification after switching to the wakeup vector. > > For now, the least awful approach is sadly to keep the vcpu_(un)blocking() hooks. > Unlike VMX's PI support, there's no fast check for an interrupt being posted (KVM > would have to rewalk the vIRR), no easy to signal the current CPU to do wakeup (I > don't think KVM even has access to the IRQ used by the owning IOMMU), and there's > no simplification of load/put code. I have an idea. Why do we even use/need the GA log? Why not, just disable the 'guest mode' in the iommu and let it sent good old normal interrupt when a vCPU is not running, just like we do when we inhibit the AVIC? GA log makes all devices that share an iommu (there are 4 iommus per package these days, some without useful devices) go through a single (!) msi like interrupt, which is even for some reason implemented by a threaded IRQ in the linux kernel. Best regards, Maxim Levitsky > > If the scheduler were changed to support waking in the sched_out path, then I'd be > more inclined to handle this in avic_vcpu_put() by rewalking the vIRR one final > time, but for now it's not worth it. > > > If I apply though only the patch series up to this patch, my fedora VM seems > > to work fine, but my windows VM still locks up hard when I run 'LatencyTop' > > in it, which doesn't happen without this patch. > > Buy "run 'LatencyTop' in it", do you mean running something in the Windows guest? > The only search results I can find for LatencyTop are Linux specific. > > > So far the symptoms I see is that on VCPU 0, ISR has quite high interrupt > > (0xe1 last time I seen it), TPR and PPR are 0xe0 (although I have seen TPR to > > have different values), and IRR has plenty of interrupts with lower priority. > > The VM seems to be stuck in this case. As if its EOI got lost or something is > > preventing the IRQ handler from issuing EOI. > > > > LatencyTop does install some form of a kernel driver which likely does meddle > > with interrupts (maybe it sends lots of self IPIs?). > > > > 100% reproducible as soon as I start monitoring with LatencyTop. > > > > Without this patch it works (or if disabling halt polling), > > Huh. I assume everything works if you disable halt polling _without_ this patch > applied? > > If so, that implies that successful halt polling without mucking with vCPU IOMMU > affinity is somehow problematic. I can't think of any relevant side effects other > than timing. >