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=-16.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 87C5BC4320A for ; Tue, 24 Aug 2021 00:55:38 +0000 (UTC) Received: from smtp2.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 53A276154B for ; Tue, 24 Aug 2021 00:55:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 53A276154B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by smtp2.osuosl.org (Postfix) with ESMTP id 1D65640388; Tue, 24 Aug 2021 00:55:38 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp2.osuosl.org ([127.0.0.1]) by localhost (smtp2.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 3NvL90YoulMv; Tue, 24 Aug 2021 00:55:34 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by smtp2.osuosl.org (Postfix) with ESMTPS id 9B6E84037C; Tue, 24 Aug 2021 00:55:33 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 73ECCC0010; Tue, 24 Aug 2021 00:55:33 +0000 (UTC) Received: from smtp3.osuosl.org (smtp3.osuosl.org [IPv6:2605:bc80:3010::136]) by lists.linuxfoundation.org (Postfix) with ESMTP id 661D2C000E for ; Tue, 24 Aug 2021 00:55:32 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp3.osuosl.org (Postfix) with ESMTP id 543EE607F2 for ; Tue, 24 Aug 2021 00:55:32 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Authentication-Results: smtp3.osuosl.org (amavisd-new); dkim=pass (2048-bit key) header.d=kernel.org Received: from smtp3.osuosl.org ([127.0.0.1]) by localhost (smtp3.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Emz-4RoZTDWG for ; Tue, 24 Aug 2021 00:55:31 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.8.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp3.osuosl.org (Postfix) with ESMTPS id A2297607F9 for ; Tue, 24 Aug 2021 00:55:31 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id A3C8B6141B; Tue, 24 Aug 2021 00:55:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1629766531; bh=zWT3e4gJTxHTTlbmAOYA9XitnOFdGdTFTMYqDai0HYI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=HIDxx0AxOLb1+c+4oh05jjKFTA6vmkhI12UCNhyAzgihscOnwRkkyJhNTOCjb1oAx Hn5CqnFyrbS0G/QZvF1zODgNq8O/ilTw/Z1nyv6TajeuOHuy6Y1ZlBmrNSi5GsZOh2 YSoSgWV7a7ZyQJZgwK/2uje0BFsO2YnS78KoxirdLdyf3pU7GseiVhtCDrDAc17JDX f8VUQSIOaNxE19peoMGetYRagRcHLG/2YhP1TZetNbzhCA1RpRrinkql7pzR54YWb9 tJty+RvKPIkJ8Gy2RZiVHP6GIr/QKZIAj3xZ5srmybVQYrVw0h2XMvkkV+WJeI40Lh 3l8yJIBSToR7Q== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH AUTOSEL 4.14 2/7] virtio: Improve vq->broken access to avoid any compiler optimization Date: Mon, 23 Aug 2021 20:55:23 -0400 Message-Id: <20210824005528.631702-2-sashal@kernel.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20210824005528.631702-1-sashal@kernel.org> References: <20210824005528.631702-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Cc: Sasha Levin , virtualization@lists.linux-foundation.org, "Michael S . Tsirkin" X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" From: Parav Pandit [ Upstream commit 60f0779862e4ab943810187752c462e85f5fa371 ] Currently vq->broken field is read by virtqueue_is_broken() in busy loop in one context by virtnet_send_command(). vq->broken is set to true in other process context by virtio_break_device(). Reader and writer are accessing it without any synchronization. This may lead to a compiler optimization which may result to optimize reading vq->broken only once. Hence, force reading vq->broken on each invocation of virtqueue_is_broken() and also force writing it so that such update is visible to the readers. It is a theoretical fix that isn't yet encountered in the field. Signed-off-by: Parav Pandit Link: https://lore.kernel.org/r/20210721142648.1525924-2-parav@nvidia.com Signed-off-by: Michael S. Tsirkin Signed-off-by: Sasha Levin --- drivers/virtio/virtio_ring.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 51278f8bd3ab..22a4329ed200 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -1198,7 +1198,7 @@ bool virtqueue_is_broken(struct virtqueue *_vq) { struct vring_virtqueue *vq = to_vvq(_vq); - return vq->broken; + return READ_ONCE(vq->broken); } EXPORT_SYMBOL_GPL(virtqueue_is_broken); @@ -1212,7 +1212,9 @@ void virtio_break_device(struct virtio_device *dev) list_for_each_entry(_vq, &dev->vqs, list) { struct vring_virtqueue *vq = to_vvq(_vq); - vq->broken = true; + + /* Pairs with READ_ONCE() in virtqueue_is_broken(). */ + WRITE_ONCE(vq->broken, true); } } EXPORT_SYMBOL_GPL(virtio_break_device); -- 2.30.2 _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization