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 4C47DC4321E for ; Mon, 18 Apr 2022 13:36:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243618AbiDRNiN (ORCPT ); Mon, 18 Apr 2022 09:38:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51360 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243920AbiDRNKg (ORCPT ); Mon, 18 Apr 2022 09:10:36 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id A5ED439159 for ; Mon, 18 Apr 2022 05:50:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1650286194; 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=HRGj6ZeyXr2MKkcn+2M4NipClwwwr9qizAjtQu5feTE=; b=RppG+vvZYDm5P1vLUGCV6E5ZyUlbMiURq3D6C8FkCAi/obYSmgwhplHnePQhlDEj0MGHpV Xr/TZMMEU1h85QMsq/b7QO22XaXh0VjBw6dsT9+C5Y5hggPw0HErhC5tVqjDsFXwoxolJp Kx8VOpBNQA6E/wdPRI1+n2vbZ2VHEhI= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-527-0yj2YEJiMemgVMRe122n-Q-1; Mon, 18 Apr 2022 08:49:52 -0400 X-MC-Unique: 0yj2YEJiMemgVMRe122n-Q-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 4A2C3299E750; Mon, 18 Apr 2022 12:49:51 +0000 (UTC) Received: from starship (unknown [10.40.194.231]) by smtp.corp.redhat.com (Postfix) with ESMTP id F305540F9D60; Mon, 18 Apr 2022 12:49:48 +0000 (UTC) Message-ID: Subject: Re: [PATCH 3/4] KVM: x86: Pend KVM_REQ_APICV_UPDATE during vCPU creation to fix a race From: Maxim Levitsky To: Sean Christopherson , Paolo Bonzini Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Gaoning Pan , Yongkang Jia Date: Mon, 18 Apr 2022 15:49:47 +0300 In-Reply-To: <20220416034249.2609491-4-seanjc@google.com> References: <20220416034249.2609491-1-seanjc@google.com> <20220416034249.2609491-4-seanjc@google.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 10.11.54.1 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2022-04-16 at 03:42 +0000, Sean Christopherson wrote: > Make a KVM_REQ_APICV_UPDATE request when creating a vCPU with an > in-kernel local APIC and APICv enabled at the module level. Consuming > kvm_apicv_activated() and stuffing vcpu->arch.apicv_active directly can > race with __kvm_set_or_clear_apicv_inhibit(), as vCPU creation happens > before the vCPU is fully onlined, i.e. it won't get the request made to > "all" vCPUs. If APICv is globally inhibited between setting apicv_active > and onlining the vCPU, the vCPU will end up running with APICv enabled > and trigger KVM's sanity check. > > Mark APICv as active during vCPU creation if APICv is enabled at the > module level, both to be optimistic about it's final state, e.g. to avoid > additional VMWRITEs on VMX, and because there are likely bugs lurking > since KVM checks apicv_active in multiple vCPU creation paths. While > keeping the current behavior of consuming kvm_apicv_activated() is > arguably safer from a regression perspective, force apicv_active so that > vCPU creation runs with deterministic state and so that if there are bugs, > they are found sooner than later, i.e. not when some crazy race condition > is hit. > > WARNING: CPU: 0 PID: 484 at arch/x86/kvm/x86.c:9877 vcpu_enter_guest+0x2ae3/0x3ee0 arch/x86/kvm/x86.c:9877 I told you that this warning catches bugs. I am not disappointed! > Modules linked in: > CPU: 0 PID: 484 Comm: syz-executor361 Not tainted 5.16.13 #2 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1~cloud0 04/01/2014 > RIP: 0010:vcpu_enter_guest+0x2ae3/0x3ee0 arch/x86/kvm/x86.c:9877 > Call Trace: > > vcpu_run arch/x86/kvm/x86.c:10039 [inline] > kvm_arch_vcpu_ioctl_run+0x337/0x15e0 arch/x86/kvm/x86.c:10234 > kvm_vcpu_ioctl+0x4d2/0xc80 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3727 > vfs_ioctl fs/ioctl.c:51 [inline] > __do_sys_ioctl fs/ioctl.c:874 [inline] > __se_sys_ioctl fs/ioctl.c:860 [inline] > __x64_sys_ioctl+0x16d/0x1d0 fs/ioctl.c:860 > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > do_syscall_64+0x38/0x90 arch/x86/entry/common.c:80 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > The bug was hit by a syzkaller spamming VM creation with 2 vCPUs and a > call to KVM_SET_GUEST_DEBUG. > > r0 = openat$kvm(0xffffffffffffff9c, &(0x7f0000000000), 0x0, 0x0) > r1 = ioctl$KVM_CREATE_VM(r0, 0xae01, 0x0) > ioctl$KVM_CAP_SPLIT_IRQCHIP(r1, 0x4068aea3, &(0x7f0000000000)) (async) > r2 = ioctl$KVM_CREATE_VCPU(r1, 0xae41, 0x0) (async) > r3 = ioctl$KVM_CREATE_VCPU(r1, 0xae41, 0x400000000000002) > ioctl$KVM_SET_GUEST_DEBUG(r3, 0x4048ae9b, &(0x7f00000000c0)={0x5dda9c14aa95f5c5}) > ioctl$KVM_RUN(r2, 0xae80, 0x0) > > Reported-by: Gaoning Pan > Reported-by: Yongkang Jia > Fixes: 8df14af42f00 ("kvm: x86: Add support for dynamic APICv activation") > Cc: stable@vger.kernel.org > Cc: Maxim Levitsky > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/x86.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 753296902535..09a270cc1c8f 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -11259,8 +11259,21 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu) > r = kvm_create_lapic(vcpu, lapic_timer_advance_ns); > if (r < 0) > goto fail_mmu_destroy; > - if (kvm_apicv_activated(vcpu->kvm)) > + > + /* > + * Defer evaluating inhibits until the vCPU is first run, as > + * this vCPU will not get notified of any changes until this > + * vCPU is visible to other vCPUs (marked online and added to > + * the set of vCPUs). Opportunistically mark APICv active as > + * VMX in particularly is highly unlikely to have inhibits. > + * Ignore the current per-VM APICv state so that vCPU creation > + * is guaranteed to run with a deterministic value, the request > + * will ensure the vCPU gets the correct state before VM-Entry. > + */ > + if (enable_apicv) { > vcpu->arch.apicv_active = true; > + kvm_make_request(KVM_REQ_APICV_UPDATE, vcpu); > + } > } else > static_branch_inc(&kvm_has_noapic_vcpu); > Makes sense. Reviewed-by: Maxim Levitsky Best regards, Maxim Levitsky