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[209.132.183.28]) by mx.google.com with ESMTPS id r21si229909qta.166.2019.08.07.00.06.44 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 07 Aug 2019 00:06:44 -0700 (PDT) Received-SPF: pass (google.com: domain of jasowang@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of jasowang@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jasowang@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 3862B30BA1B4; Wed, 7 Aug 2019 07:06:44 +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 A47591001284; Wed, 7 Aug 2019 07:06:39 +0000 (UTC) From: Jason Wang To: mst@redhat.com, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, jgg@ziepe.ca, Jason Wang Subject: [PATCH V4 6/9] vhost: don't do synchronize_rcu() in vhost_uninit_vq_maps() Date: Wed, 7 Aug 2019 03:06:14 -0400 Message-Id: <20190807070617.23716-7-jasowang@redhat.com> In-Reply-To: <20190807070617.23716-1-jasowang@redhat.com> References: <20190807070617.23716-1-jasowang@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Wed, 07 Aug 2019 07:06:44 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: X-Virus-Scanned: ClamAV using ClamSMTP 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 c12cdadb0855..cfc11f9ed9c9 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -333,7 +333,9 @@ 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])