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=unavailable 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 008D2C636CB for ; Mon, 19 Jul 2021 09:58:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E1F3F61182 for ; Mon, 19 Jul 2021 09:58:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236224AbhGSJSG (ORCPT ); Mon, 19 Jul 2021 05:18:06 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:37802 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236185AbhGSJSF (ORCPT ); Mon, 19 Jul 2021 05:18:05 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1626688725; 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=9iuXMiXB3koc/GvJU+Wg2k7jYKX5Po4q4IzNF0aqa3Y=; b=hb4L+ULsGFBoTF6ShuSTReiVSAVwKsaEAow/PCi8Ybct3Xl+TABrsLpL3XbuJlEKa1kejI x3BR9wmr0eGmbrYZd58jM9VEdFq8WbiIg59FH5b+nF8rXoCDA+rBLehJ6L+kwhDCBQYqPL /PZ+TnJj5rGn/5rC2G7wTxBqMSRcSqk= 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-359-36K-_R-8PYmpgC70XqLYyg-1; Mon, 19 Jul 2021 05:58:43 -0400 X-MC-Unique: 36K-_R-8PYmpgC70XqLYyg-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C4E32362FD; Mon, 19 Jul 2021 09:58:41 +0000 (UTC) Received: from starship (unknown [10.40.192.10]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0826A10074FD; Mon, 19 Jul 2021 09:58:37 +0000 (UTC) Message-ID: <779741344dc401aa572c8c9bea05e059afe9a6d2.camel@redhat.com> Subject: Re: [PATCH v2 8/8] KVM: x86: hyper-v: Deactivate APICv only when AutoEOI feature is in use From: Maxim Levitsky To: Vitaly Kuznetsov , kvm@vger.kernel.org Cc: "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , Jim Mattson , Joerg Roedel , Borislav Petkov , Wanpeng Li , Paolo Bonzini , Thomas Gleixner , "H. Peter Anvin" , Ingo Molnar , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , Sean Christopherson Date: Mon, 19 Jul 2021 12:58:36 +0300 In-Reply-To: <87tukqzmg7.fsf@vitty.brq.redhat.com> References: <20210713142023.106183-1-mlevitsk@redhat.com> <20210713142023.106183-9-mlevitsk@redhat.com> <87wnpmzqw3.fsf@vitty.brq.redhat.com> <87tukqzmg7.fsf@vitty.brq.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 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2021-07-19 at 11:23 +0200, Vitaly Kuznetsov wrote: > Maxim Levitsky writes: > > > On Mon, 2021-07-19 at 09:47 +0200, Vitaly Kuznetsov wrote: > > > Maxim Levitsky writes: > > > > > > > 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. > > > > > > > > > > Would it be possible to use some magic value in 'vcpu->srcu_idx' and not > > > introduce a new 'srcu_ls_locked' flag? > > > > Well, currently the returned index value from srcu_read_lock is opaque > > (and we have two SRCU implementations and both I think return small positive numbers, > > but I haven't studied them in depth). > > > > We can ask the people that maintain SRCU to reserve a number (like -1) > > or so. > > I probably first add the 'srcu_is_locked' thought and then as a follow up patch > > remove it if they agree. > > > > Ah, OK. BTW, I've just discovered srcu_read_lock_held() which sounds > like the function we need but unfortunately it is not. Yea, exactly this. :-( Best regards, Maxim Levitsky >