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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 60C38C7618E for ; Tue, 23 Jul 2019 07:58:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 382B92239F for ; Tue, 23 Jul 2019 07:58:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388734AbfGWH6N (ORCPT ); Tue, 23 Jul 2019 03:58:13 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37532 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726989AbfGWH6J (ORCPT ); Tue, 23 Jul 2019 03:58:09 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 3C5BD335E7; Tue, 23 Jul 2019 07:58:09 +0000 (UTC) Received: from hp-dl380pg8-01.lab.eng.pek2.redhat.com (hp-dl380pg8-01.lab.eng.pek2.redhat.com [10.73.8.10]) by smtp.corp.redhat.com (Postfix) with ESMTP id C210E608A5; Tue, 23 Jul 2019 07:57:57 +0000 (UTC) From: Jason Wang To: mst@redhat.com, jasowang@redhat.com Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 6/6] vhost: don't do synchronize_rcu() in vhost_uninit_vq_maps() Date: Tue, 23 Jul 2019 03:57:18 -0400 Message-Id: <20190723075718.6275-7-jasowang@redhat.com> In-Reply-To: <20190723075718.6275-1-jasowang@redhat.com> References: <20190723075718.6275-1-jasowang@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Tue, 23 Jul 2019 07:58:09 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org There's no need for RCU synchronization in vhost_uninit_vq_maps() since we've already serialized with readers (memory accessors). This also avoid the possible userspace DOS through ioctl() because of the possible high latency caused by synchronize_rcu(). Reported-by: Michael S. Tsirkin Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual address") Signed-off-by: Jason Wang --- drivers/vhost/vhost.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 5b8821d00fe4..a17df1f4069a 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -334,7 +334,9 @@ static void vhost_uninit_vq_maps(struct vhost_virtqueue *vq) } spin_unlock(&vq->mmu_lock); - synchronize_rcu(); + /* No need for synchronize_rcu() or kfree_rcu() since we are + * serialized with memory accessors (e.g vq mutex held). + */ for (i = 0; i < VHOST_NUM_ADDRS; i++) if (map[i]) -- 2.18.1