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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 DED41C76194 for ; Tue, 23 Jul 2019 13:25:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C1F1122353 for ; Tue, 23 Jul 2019 13:25:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390183AbfGWNZY (ORCPT ); Tue, 23 Jul 2019 09:25:24 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38174 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725778AbfGWNZY (ORCPT ); Tue, 23 Jul 2019 09:25:24 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 0EC44C057F2E; Tue, 23 Jul 2019 13:25:24 +0000 (UTC) Received: from [10.72.12.26] (ovpn-12-26.pek2.redhat.com [10.72.12.26]) by smtp.corp.redhat.com (Postfix) with ESMTP id C709C5B685; Tue, 23 Jul 2019 13:25:18 +0000 (UTC) Subject: Re: [PATCH 4/6] vhost: reset invalidate_count in vhost_set_vring_num_addr() To: "Michael S. Tsirkin" Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <20190723075718.6275-1-jasowang@redhat.com> <20190723075718.6275-5-jasowang@redhat.com> <20190723042143-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: <4e52f1cb-f805-18f6-d50b-1379298de2e3@redhat.com> Date: Tue, 23 Jul 2019 21:25:22 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190723042143-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Tue, 23 Jul 2019 13:25:24 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/7/23 下午5:17, Michael S. Tsirkin wrote: > On Tue, Jul 23, 2019 at 03:57:16AM -0400, Jason Wang wrote: >> The vhost_set_vring_num_addr() could be called in the middle of >> invalidate_range_start() and invalidate_range_end(). If we don't reset >> invalidate_count after the un-registering of MMU notifier, the >> invalidate_cont will run out of sync (e.g never reach zero). This will >> in fact disable the fast accessor path. Fixing by reset the count to >> zero. >> >> 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, 4 insertions(+) >> >> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c >> index 03666b702498..89c9f08b5146 100644 >> --- a/drivers/vhost/vhost.c >> +++ b/drivers/vhost/vhost.c >> @@ -2074,6 +2074,10 @@ static long vhost_vring_set_num_addr(struct vhost_dev *d, >> d->has_notifier = false; >> } >> >> + /* reset invalidate_count in case we are in the middle of >> + * invalidate_start() and invalidate_end(). >> + */ >> + vq->invalidate_count = 0; > I think that the code is ok but the comments are not very clear: > - we are never in the middle since we just removed the notifier If I read the code correctly, mmu_notifier_unregister() can only guarantee to wait for the pending method to complete. So we can have: invalidate_start() mmu_notifier_unregister() invalidate_end() > - the result is not just disabling optimization: > if notifier becomes negative, then later we > can think it's ok to map when it isn't since > notifier is active. I don't get how it could be negative, the only possible thing is to have a positive value. Thanks > >> vhost_uninit_vq_maps(vq); >> #endif >> >> -- >> 2.18.1