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=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 D27B7C7618B for ; Tue, 23 Jul 2019 09:17:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A9BA3227B9 for ; Tue, 23 Jul 2019 09:17:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388912AbfGWJRe (ORCPT ); Tue, 23 Jul 2019 05:17:34 -0400 Received: from mail-qk1-f193.google.com ([209.85.222.193]:41793 "EHLO mail-qk1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727722AbfGWJRe (ORCPT ); Tue, 23 Jul 2019 05:17:34 -0400 Received: by mail-qk1-f193.google.com with SMTP id v22so30563855qkj.8 for ; Tue, 23 Jul 2019 02:17:34 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=zIMuDv+zk7S1NCvH0qhLppn9YRoVaxQzRUcA6IGuXcs=; b=IyUjX5CRKbTCbTb3d543lfy22o5zLL1aIBbnBdqT8i+6Xd0AxeEEMAcvi5AHIFu0yn CkmEnY/HRrEyeLkrZQupiI6PFCLSD6E7kbqXB/dlkQwEgqmgrZvz6iYVGoTfIQae+8Q/ gUzBVU8SE2QCavAvlj2YnB1fZpKlTJWnadBxjioHCpM1IeB5dn+GEcjFV3nLKtdzvFoL 1BOzU4MYD6fVYeohMPE/fKErFR4SNuOThdc6P1idFfdei16DgOkaYp6gqV85mWzGeqBa SUxmrT6A1aZI9pfCmBXsAg7qLF/t/1XelK8uWaA05xp/9tfcmdru3w248BQDKuC4ZtnL WxVA== X-Gm-Message-State: APjAAAVZ6xsO0EGbj13H5NSI7kaLqJy0ZjUSFn1ir0HkWclzxbh2ER8N Nt8QqIFYwLhQT4APXpikAabFjQ== X-Google-Smtp-Source: APXvYqxCxrHJb2/RQUMnbweSxs5Cq2YkuyrJJ0kQghMt/IAIFI53AquzBnAmUMtJGKkqG286t9N46w== X-Received: by 2002:a37:646:: with SMTP id 67mr47571333qkg.287.1563873453656; Tue, 23 Jul 2019 02:17:33 -0700 (PDT) Received: from redhat.com (bzq-79-181-91-42.red.bezeqint.net. [79.181.91.42]) by smtp.gmail.com with ESMTPSA id g54sm25451794qtc.61.2019.07.23.02.17.31 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 23 Jul 2019 02:17:32 -0700 (PDT) Date: Tue, 23 Jul 2019 05:17:28 -0400 From: "Michael S. Tsirkin" To: Jason Wang Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/6] vhost: reset invalidate_count in vhost_set_vring_num_addr() Message-ID: <20190723042143-mutt-send-email-mst@kernel.org> References: <20190723075718.6275-1-jasowang@redhat.com> <20190723075718.6275-5-jasowang@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190723075718.6275-5-jasowang@redhat.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 - 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. > vhost_uninit_vq_maps(vq); > #endif > > -- > 2.18.1