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=-17.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 13B77C636C8 for ; Sun, 18 Jul 2021 12:13:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DA62F6113D for ; Sun, 18 Jul 2021 12:13:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233221AbhGRMQb (ORCPT ); Sun, 18 Jul 2021 08:16:31 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:26089 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232851AbhGRMQa (ORCPT ); Sun, 18 Jul 2021 08:16:30 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1626610411; 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=LIksOM0j+7t5HBnHvU6n/LtoJcl7Qg9Ivf/K/Xcj45Q=; b=IMm2hKOoehktjo6mwZVSvj8Fn5wBltPfJ4qZCgIX2dny6vFoD4EMKLBNEMvjo3zfeyZ475 0Fi4UP0Kg0jXqb6wHiMPavnjvUTVHh4QMSYgC1SLcyOuHXR/swJZprE/tlw3ZI2G+2KwCa XM9MmFW2wpSMTTKSKj5RgEwajg5gTRE= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-239-rkzElNt0OHmCmPOe25WG2Q-1; Sun, 18 Jul 2021 08:13:30 -0400 X-MC-Unique: rkzElNt0OHmCmPOe25WG2Q-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 40EBE1835AC2; Sun, 18 Jul 2021 12:13:28 +0000 (UTC) Received: from starship (unknown [10.40.192.10]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4C7995D6A1; Sun, 18 Jul 2021 12:13:22 +0000 (UTC) Message-ID: Subject: Re: [PATCH v2 8/8] KVM: x86: hyper-v: Deactivate APICv only when AutoEOI feature is in use From: Maxim Levitsky To: kvm@vger.kernel.org Cc: "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , Jim Mattson , Joerg Roedel , Borislav Petkov , Vitaly Kuznetsov , Wanpeng Li , Paolo Bonzini , Thomas Gleixner , "H. Peter Anvin" , Ingo Molnar , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , Sean Christopherson Date: Sun, 18 Jul 2021 15:13:21 +0300 In-Reply-To: <20210713142023.106183-9-mlevitsk@redhat.com> References: <20210713142023.106183-1-mlevitsk@redhat.com> <20210713142023.106183-9-mlevitsk@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 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2021-07-13 at 17:20 +0300, Maxim Levitsky wrote: > From: Vitaly Kuznetsov > > APICV_INHIBIT_REASON_HYPERV is currently unconditionally forced upon > SynIC activation as SynIC's AutoEOI is incompatible with APICv/AVIC. It is, > however, possible to track whether the feature was actually used by the > guest and only inhibit APICv/AVIC when needed. > > TLFS suggests a dedicated 'HV_DEPRECATING_AEOI_RECOMMENDED' flag to let > Windows know that AutoEOI feature should be avoided. While it's up to > KVM userspace to set the flag, KVM can help a bit by exposing global > APICv/AVIC enablement: in case APICv/AVIC usage is impossible, AutoEOI > is still preferred. > > Maxim: > - added SRCU lock drop around call to kvm_request_apicv_update > - always set HV_DEPRECATING_AEOI_RECOMMENDED in kvm_get_hv_cpuid, > since this feature can be used regardless of AVIC > > Signed-off-by: Vitaly Kuznetsov > Signed-off-by: Maxim Levitsky > --- > arch/x86/include/asm/kvm_host.h | 3 +++ > arch/x86/kvm/hyperv.c | 34 +++++++++++++++++++++++++++------ > 2 files changed, 31 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index e11d64aa0bcd..f900dca58af8 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -956,6 +956,9 @@ struct kvm_hv { > /* How many vCPUs have VP index != vCPU index */ > atomic_t num_mismatched_vp_indexes; > > + /* How many SynICs use 'AutoEOI' feature */ > + atomic_t synic_auto_eoi_used; > + > struct hv_partition_assist_pg *hv_pa_pg; > struct kvm_hv_syndbg hv_syndbg; > }; > diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c > index b07592ca92f0..6bf47a583d0e 100644 > --- a/arch/x86/kvm/hyperv.c > +++ b/arch/x86/kvm/hyperv.c > @@ -85,9 +85,22 @@ static bool synic_has_vector_auto_eoi(struct kvm_vcpu_hv_synic *synic, > return false; > } > > + > +static void synic_toggle_avic(struct kvm_vcpu *vcpu, bool activate) > +{ > + srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx); > + kvm_request_apicv_update(vcpu->kvm, activate, > + APICV_INHIBIT_REASON_HYPERV); > + vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu); > +} Well turns out that this patch still doesn't work (on this weekend I found out that all my AVIC enabled VMs hang on reboot). I finally found out what prompted me back then to make srcu lock drop in synic_update_vector conditional on whether the write was done by the host. Turns out that while KVM_SET_MSRS does take the kvm->srcu lock, it stores the returned srcu index in a local variable and not in vcpu->srcu_idx, thus the lock drop in synic_toggle_avic doesn't work. So it is likely that I have seen it not work, and blamed KVM_SET_MSRS for not taking the srcu lock which was a wrong assumption. I am more inclined to fix this by just tracking if we hold the srcu lock on each VCPU manually, just as we track the srcu index anyway, and then kvm_request_apicv_update can use this to drop the srcu lock when needed. > + > static void synic_update_vector(struct kvm_vcpu_hv_synic *synic, > int vector) > { > + struct kvm_vcpu *vcpu = hv_synic_to_vcpu(synic); > + struct kvm_hv *hv = to_kvm_hv(vcpu->kvm); > + int auto_eoi_old, auto_eoi_new; > + > if (vector < HV_SYNIC_FIRST_VALID_VECTOR) > return; > > @@ -96,10 +109,23 @@ static void synic_update_vector(struct kvm_vcpu_hv_synic *synic, > else > __clear_bit(vector, synic->vec_bitmap); > > + auto_eoi_old = bitmap_weight(synic->auto_eoi_bitmap, 256); > + > if (synic_has_vector_auto_eoi(synic, vector)) > __set_bit(vector, synic->auto_eoi_bitmap); > else > __clear_bit(vector, synic->auto_eoi_bitmap); > + > + auto_eoi_new = bitmap_weight(synic->auto_eoi_bitmap, 256); > + > + /* Hyper-V SynIC auto EOI SINTs are not compatible with APICV */ > + if (!auto_eoi_old && auto_eoi_new) { > + if (atomic_inc_return(&hv->synic_auto_eoi_used) == 1) > + synic_toggle_avic(vcpu, false); > + } else if (!auto_eoi_new && auto_eoi_old) { > + if (atomic_dec_return(&hv->synic_auto_eoi_used) == 0) > + synic_toggle_avic(vcpu, true); > + } > } > > static int synic_set_sint(struct kvm_vcpu_hv_synic *synic, int sint, > @@ -933,12 +959,6 @@ int kvm_hv_activate_synic(struct kvm_vcpu *vcpu, bool dont_zero_synic_pages) > > synic = to_hv_synic(vcpu); > > - /* > - * Hyper-V SynIC auto EOI SINT's are > - * not compatible with APICV, so request > - * to deactivate APICV permanently. > - */ > - kvm_request_apicv_update(vcpu->kvm, false, APICV_INHIBIT_REASON_HYPERV); > synic->active = true; > synic->dont_zero_synic_pages = dont_zero_synic_pages; > synic->control = HV_SYNIC_CONTROL_ENABLE; > @@ -2466,6 +2486,8 @@ int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid, > ent->eax |= HV_X64_ENLIGHTENED_VMCS_RECOMMENDED; > if (!cpu_smt_possible()) > ent->eax |= HV_X64_NO_NONARCH_CORESHARING; > + > + ent->eax |= HV_DEPRECATING_AEOI_RECOMMENDED; Vitally, I would like to hear your opinion on this change I also made to your code. I think that we should always expose HV_DEPRECATING_AEOI_RECOMMENDED as a supported HV cpuid bit regardless of AVIC, so that qemu could set it regardless of AVIC in the kernel, even if this is not optimal. Best regards, Maxim Levitsky > /* > * Default number of spinlock retry attempts, matches > * HyperV 2016.