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=-19.1 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, URIBL_BLOCKED,USER_AGENT_GIT 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 38942C4363C for ; Mon, 17 May 2021 15:45:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1BEFC61108 for ; Mon, 17 May 2021 15:45:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344890AbhEQPpx (ORCPT ); Mon, 17 May 2021 11:45:53 -0400 Received: from mail.kernel.org ([198.145.29.99]:55194 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245694AbhEQPad (ORCPT ); Mon, 17 May 2021 11:30:33 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 5352E61CC4; Mon, 17 May 2021 14:37:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1621262273; bh=a+76ESXoPOw3Ev4y4VzpXrP8duFzucx1aof+adZ6SJk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Ck3hCiq2Umf7/7HI6XlRAGsZu65k1fGjAyWvdgeh04JCG1mm2zXWHaqm8wC/VHQ08 C2Op/NBSQIGN6r8U2HhKptfyo/FhVl42Xufg4uIkiW5k6mtFgyYkFNtwgEMOff44ZK 8/z0WucLKsKI1zwPasdfy+MRjM9CdT6qrC5Y8lGE= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot+6beae4000559d41d80f8@syzkaller.appspotmail.com, Thomas Gleixner , Paolo Bonzini , Sasha Levin Subject: [PATCH 5.11 254/329] KVM: x86: Prevent deadlock against tk_core.seq Date: Mon, 17 May 2021 16:02:45 +0200 Message-Id: <20210517140310.699634146@linuxfoundation.org> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210517140302.043055203@linuxfoundation.org> References: <20210517140302.043055203@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Thomas Gleixner [ Upstream commit 3f804f6d201ca93adf4c3df04d1bfd152c1129d6 ] syzbot reported a possible deadlock in pvclock_gtod_notify(): CPU 0 CPU 1 write_seqcount_begin(&tk_core.seq); pvclock_gtod_notify() spin_lock(&pool->lock); queue_work(..., &pvclock_gtod_work) ktime_get() spin_lock(&pool->lock); do { seq = read_seqcount_begin(tk_core.seq) ... } while (read_seqcount_retry(&tk_core.seq, seq); While this is unlikely to happen, it's possible. Delegate queue_work() to irq_work() which postpones it until the tk_core.seq write held region is left and interrupts are reenabled. Fixes: 16e8d74d2da9 ("KVM: x86: notifier for clocksource changes") Reported-by: syzbot+6beae4000559d41d80f8@syzkaller.appspotmail.com Signed-off-by: Thomas Gleixner Message-Id: <87h7jgm1zy.ffs@nanos.tec.linutronix.de> Signed-off-by: Paolo Bonzini Signed-off-by: Sasha Levin --- arch/x86/kvm/x86.c | 22 ++++++++++++++++++---- 1 file changed, 18 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index b010ad6cbd14..8105e9ae1ff8 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -7872,6 +7872,18 @@ static void pvclock_gtod_update_fn(struct work_struct *work) static DECLARE_WORK(pvclock_gtod_work, pvclock_gtod_update_fn); +/* + * Indirection to move queue_work() out of the tk_core.seq write held + * region to prevent possible deadlocks against time accessors which + * are invoked with work related locks held. + */ +static void pvclock_irq_work_fn(struct irq_work *w) +{ + queue_work(system_long_wq, &pvclock_gtod_work); +} + +static DEFINE_IRQ_WORK(pvclock_irq_work, pvclock_irq_work_fn); + /* * Notification about pvclock gtod data update. */ @@ -7883,13 +7895,14 @@ static int pvclock_gtod_notify(struct notifier_block *nb, unsigned long unused, update_pvclock_gtod(tk); - /* disable master clock if host does not trust, or does not - * use, TSC based clocksource. + /* + * Disable master clock if host does not trust, or does not use, + * TSC based clocksource. Delegate queue_work() to irq_work as + * this is invoked with tk_core.seq write held. */ if (!gtod_is_based_on_tsc(gtod->clock.vclock_mode) && atomic_read(&kvm_guest_has_master_clock) != 0) - queue_work(system_long_wq, &pvclock_gtod_work); - + irq_work_queue(&pvclock_irq_work); return 0; } @@ -8005,6 +8018,7 @@ void kvm_arch_exit(void) cpuhp_remove_state_nocalls(CPUHP_AP_X86_KVM_CLK_ONLINE); #ifdef CONFIG_X86_64 pvclock_gtod_unregister_notifier(&pvclock_gtod_notifier); + irq_work_sync(&pvclock_irq_work); cancel_work_sync(&pvclock_gtod_work); #endif kvm_x86_ops.hardware_enable = NULL; -- 2.30.2