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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0A15DC433EF for ; Tue, 26 Oct 2021 03:12:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DB13261078 for ; Tue, 26 Oct 2021 03:12:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234545AbhJZDPR (ORCPT ); Mon, 25 Oct 2021 23:15:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44344 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233243AbhJZDPQ (ORCPT ); Mon, 25 Oct 2021 23:15:16 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6055BC061745 for ; Mon, 25 Oct 2021 20:12:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=MIME-Version:Content-Type:Date:Cc:To: From:Subject:Message-ID:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:In-Reply-To:References; bh=adApSZdYFI7D6gASGouAH73cZexc2o75mkLavqOrHkQ=; b=g42hwq1mOHXt7kCfDuGsgnHQsW 66z3Ya4nvKM2DGSLi8Yx8ipKCv/F+MQ41MQqGC1h0Vb7VD1xH3GPxR/bbOZRuHfS/D/D1BMWuZtgb TObxP0vSFsMTOOwKajlZygehL0X2Xta0DVT11pRliG9/Fs3lqTRqz+DTq/Had5+ayKd5mbge5cQAN eEyPK4NBJDGqEtm7sTow1C2+9rnwDsgvU5XE2Zbi3uLgyDWSKGHtkZIYiXzeY0K0oING4V/nCf3Ih LEbIEt6ALhYJrUmIf++CquNAWsTMhbO3gcBm9vPcwQMBzgIoae27/i8jMU7dPvIL+wj8r38Mkv3pO p9H0mn/w==; Received: from [2001:8b0:10b:1::3ae] (helo=u3832b3a9db3152.ant.amazon.com) by bombadil.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1mfCtF-000WGx-Dd; Tue, 26 Oct 2021 03:12:41 +0000 Message-ID: <606aaaf29fca3850a63aa4499826104e77a72346.camel@infradead.org> Subject: [PATCH] KVM: x86: Take srcu lock in post_kvm_run_save() From: David Woodhouse To: kvm Cc: Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , mtosatti Date: Tue, 26 Oct 2021 04:12:38 +0100 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-OmkgNCmq8NVRoUR5zKCU" User-Agent: Evolution 3.36.5-0ubuntu1 MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org --=-OmkgNCmq8NVRoUR5zKCU Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable From: David Woodhouse The Xen interrupt injection for event channels relies on accessing the guest's vcpu_info structure in __kvm_xen_has_interrupt(), through a gfn_to_hva_cache. This requires the srcu lock to be held, which is mostly the case except for this code path: [ 11.822877] WARNING: suspicious RCU usage [ 11.822965] ----------------------------- [ 11.823013] include/linux/kvm_host.h:664 suspicious rcu_dereference_chec= k() usage! [ 11.823131] [ 11.823131] other info that might help us debug this: [ 11.823131] [ 11.823196] [ 11.823196] rcu_scheduler_active =3D 2, debug_locks =3D 1 [ 11.823253] 1 lock held by dom:0/90: [ 11.823292] #0: ffff998956ec8118 (&vcpu->mutex){+.+.}, at: kvm_vcpu_ioc= tl+0x85/0x680 [ 11.823379] [ 11.823379] stack backtrace: [ 11.823428] CPU: 2 PID: 90 Comm: dom:0 Kdump: loaded Not tainted 5.4.34+= #5 [ 11.823496] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel= -1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 04/01/2014 [ 11.823612] Call Trace: [ 11.823645] dump_stack+0x7a/0xa5 [ 11.823681] lockdep_rcu_suspicious+0xc5/0x100 [ 11.823726] __kvm_xen_has_interrupt+0x179/0x190 [ 11.823773] kvm_cpu_has_extint+0x6d/0x90 [ 11.823813] kvm_cpu_accept_dm_intr+0xd/0x40 [ 11.823853] kvm_vcpu_ready_for_interrupt_injection+0x20/0x30 < post_kvm_run_save() inlined here > [ 11.823906] kvm_arch_vcpu_ioctl_run+0x135/0x6a0 [ 11.823947] kvm_vcpu_ioctl+0x263/0x680 Fixes: 40da8ccd724f ("KVM: x86/xen: Add event channel interrupt vector upca= ll") Signed-off-by: David Woodhouse --- There are potentially other ways of doing this, by shuffling the tail of kvm_arch_vcpu_ioctl_run() around a little and holding the lock once there instead of taking it within vcpu_run(). But the call to post_kvm_run_save() occurs even on the error paths, and it gets complex to untangle. This is the simple approach. This doesn't show up when I enable event channel delivery in xen_shinfo_test because we have pic_in_kernel() there. I'll fix the tests not to hardcode that, as I expand the event channel support and add more testing of it. arch/x86/kvm/x86.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index f0874c3d12ce..cd42d58008f7 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -8783,9 +8783,17 @@ static void post_kvm_run_save(struct kvm_vcpu *vcpu) =20 kvm_run->cr8 =3D kvm_get_cr8(vcpu); kvm_run->apic_base =3D kvm_get_apic_base(vcpu); + + /* + * The call to kvm_ready_for_interrupt_injection() may end up in + * kvm_xen_has_interrupt() which may require the srcu lock to be + * held to protect against changes in the vcpu_info address. + */ + vcpu->srcu_idx =3D srcu_read_lock(&vcpu->kvm->srcu); kvm_run->ready_for_interrupt_injection =3D pic_in_kernel(vcpu->kvm) || kvm_vcpu_ready_for_interrupt_injection(vcpu); + srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx); =20 if (is_smm(vcpu)) kvm_run->flags |=3D KVM_RUN_X86_SMM; --=20 2.25.1 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