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 5E55DC433EF for ; Wed, 20 Apr 2022 01:37:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1358807AbiDTBka (ORCPT ); Tue, 19 Apr 2022 21:40:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43852 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1358781AbiDTBkY (ORCPT ); Tue, 19 Apr 2022 21:40:24 -0400 Received: from mail-pg1-x549.google.com (mail-pg1-x549.google.com [IPv6:2607:f8b0:4864:20::549]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C6DA537A01 for ; Tue, 19 Apr 2022 18:37:39 -0700 (PDT) Received: by mail-pg1-x549.google.com with SMTP id z18-20020a631912000000b003a392265b64so120443pgl.2 for ; Tue, 19 Apr 2022 18:37:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=reply-to:date:in-reply-to:message-id:mime-version:references :subject:from:to:cc; bh=L1stsYTq2+o/6GoWODILUnSJjjIl65dFiA+39DN8K4w=; b=ZMA4b3z5Kp6xkhw0yjW/G39Dez/b7Qemsfz+FioG2pKkA3z2jwQ3Iwn190Ta8xbdP6 Ll4Dky1fhRre8DqfzA51Lgk0kxknA0hpq8t130a2RWlu+uaxVbQu8bI0BKxFGFoIgUoY 0j4gPkCN6uYWLLqHNZ7PEyZLMVfeBJXWPMJoxk5P0x9PLsV3BCHZI/YcaF5FEmnnIjsl o6Wx1dhwMmyJ019aiCOSZ+sce3LdwmlXmYoFOH8uGYMIA0S42XMD9pmtS7er1qrxn+jQ ROoBkApqvFpxFBU/p/Q98xFIlyFGgXAWBYvXjf0AGN2e63I7Upf3T/alg4TfuAE4hGZn vMmw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:reply-to:date:in-reply-to:message-id :mime-version:references:subject:from:to:cc; bh=L1stsYTq2+o/6GoWODILUnSJjjIl65dFiA+39DN8K4w=; b=6j87O5bwZkiGIlnmAWtYaULEkws58zwRqGN97PHtxkX1anwf4TOkAHQa1Pov72sAoQ r/j71tiORcya+WSxi6iuwtW3OuR/wPAnXrWRqxvyn5pejLnjfVfCLEzOxMThWuNoHU3d xLeHISn5dq6gySD7uF8fZ1/VBxmgK2k6zwwYZ3hymVqFEhKCsJtePytJ/Pxa/lFDClPP Je9eXePqvh5/4NAg+n0G5O7XINAieWsUxjgkmvYpZ+UdgcQuP9b2ujURDUc2GdqnKkch SHvbQaqkbe0iPwqnVQJKdw2xcIP8JqdDVCoZhxo61qpZMQlFqX/ENKQVuGmTskMCTa+b MQCA== X-Gm-Message-State: AOAM532dbe6SwcPn8FRpWEmAJIKXlsPiibMRA1laxuSt4DfjS1OhX9jh 4sgF8dx8/bpu+io76DXHcrKYx/4RL1w= X-Google-Smtp-Source: ABdhPJzGw3h6ARA9+CPHD3Vzsl9+lRkjgJdWEettAnhoScwY554OuC5PnW5lIQmpCPuIWYJQ+Q+wRnGFffg= X-Received: from seanjc.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:3e5]) (user=seanjc job=sendgmr) by 2002:a62:1c8d:0:b0:4fa:8dcb:6da2 with SMTP id c135-20020a621c8d000000b004fa8dcb6da2mr20533553pfc.19.1650418659302; Tue, 19 Apr 2022 18:37:39 -0700 (PDT) Reply-To: Sean Christopherson Date: Wed, 20 Apr 2022 01:37:31 +0000 In-Reply-To: <20220420013732.3308816-1-seanjc@google.com> Message-Id: <20220420013732.3308816-4-seanjc@google.com> Mime-Version: 1.0 References: <20220420013732.3308816-1-seanjc@google.com> X-Mailer: git-send-email 2.36.0.rc0.470.gd361397f0d-goog Subject: [PATCH v2 3/4] KVM: x86: Pend KVM_REQ_APICV_UPDATE during vCPU creation to fix a race From: Sean Christopherson To: Paolo Bonzini Cc: Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Maxim Levitsky , Gaoning Pan , Yongkang Jia Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 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 Reviewed-by: Maxim Levitsky --- 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); -- 2.36.0.rc0.470.gd361397f0d-goog