From patchwork Thu Jul 14 22:44:10 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 12918535 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C353AC43334 for ; Thu, 14 Jul 2022 22:44:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231153AbiGNWoT (ORCPT ); Thu, 14 Jul 2022 18:44:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53604 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229481AbiGNWoS (ORCPT ); Thu, 14 Jul 2022 18:44:18 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A8CAC66AF6; Thu, 14 Jul 2022 15:44:17 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 5E333B829DF; Thu, 14 Jul 2022 22:44:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EDE5DC34114; Thu, 14 Jul 2022 22:44:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1657838654; bh=ZTNaD7TTclpn13DZH9gmDu/kVHAK0vU6nq05MFNP/OI=; h=From:To:Cc:Subject:Date:From; b=OeQS1awqXop0peSKh0A2dyghSIgn/D6oI+ww24QPmvMecatn8NjCA7FnNbTxEA1a/ jFfq/8eoAnF4reSH3Zx5kRBPZtq+YrIOM8HKBzJObtP2Ce3WAxlCRQiGY63uEN5Hen DXyg1enx4YljQAw7SN2WDuLqa7+SvA0Tirs62KT5LpVuYOAhBNesaRbael/3jB9R3e Ipu0Z9Ok3f1qtPoAtUizrTvfyKyZgfT1XWtlp8dlj7SLkFReNxP74nx3isQPvw2C6h h0ATw8BT5o2FV9ZpvVEjQMzburXRmJx+x+EICrJ/Hog1ZVlmG8L60Q+0d9vLU8VYyC PbhWXmyYeRo0w== From: SeongJae Park To: roger.pau@citrix.com Cc: axboe@kernel.dk, boris.ostrovsky@oracle.com, jgross@suse.com, mheyne@amazon.de, xen-devel@lists.xenproject.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, SeongJae Park , stable@vger.kernel.org Subject: [PATCH v2] xen-blkback: fix persistent grants negotiation Date: Thu, 14 Jul 2022 22:44:10 +0000 Message-Id: <20220714224410.51147-1-sj@kernel.org> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Persistent grants feature can be used only when both backend and the frontend supports the feature. The feature was always supported by 'blkback', but commit aac8a70db24b ("xen-blkback: add a parameter for disabling of persistent grants") has introduced a parameter for disabling it runtime. To avoid the parameter be updated while being used by 'blkback', the commit caches the parameter into 'vbd->feature_gnt_persistent' in 'xen_vbd_create()', and then check if the guest also supports the feature and finally updates the field in 'connect_ring()'. However, 'connect_ring()' could be called before 'xen_vbd_create()', so later execution of 'xen_vbd_create()' can wrongly overwrite 'true' to 'vbd->feature_gnt_persistent'. As a result, 'blkback' could try to use 'persistent grants' feature even if the guest doesn't support the feature. This commit fixes the issue by moving the parameter value caching to 'xen_blkif_alloc()', which allocates the 'blkif'. Because the struct embeds 'vbd' object, which will be used by 'connect_ring()' later, this should be called before 'connect_ring()' and therefore this should be the right and safe place to do the caching. Fixes: aac8a70db24b ("xen-blkback: add a parameter for disabling of persistent grants") Cc: # 5.10.x Signed-off-by: Maximilian Heyne Signed-off-by: SeongJae Park --- Changes from v1[1] - Avoid the behavioral change[2] - Rebase on latest xen/tip/linux-next - Re-work by SeongJae Park - Cc stable@ [1] https://lore.kernel.org/xen-devel/20220106091013.126076-1-mheyne@amazon.de/ [2] https://lore.kernel.org/xen-devel/20220121102309.27802-1-sj@kernel.org/ drivers/block/xen-blkback/xenbus.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-) diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index 97de13b14175..16c6785d260c 100644 --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -157,6 +157,11 @@ static int xen_blkif_alloc_rings(struct xen_blkif *blkif) return 0; } +/* Enable the persistent grants feature. */ +static bool feature_persistent = true; +module_param(feature_persistent, bool, 0644); +MODULE_PARM_DESC(feature_persistent, "Enables the persistent grants feature"); + static struct xen_blkif *xen_blkif_alloc(domid_t domid) { struct xen_blkif *blkif; @@ -181,6 +186,8 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid) __module_get(THIS_MODULE); INIT_WORK(&blkif->free_work, xen_blkif_deferred_free); + blkif->vbd.feature_gnt_persistent = feature_persistent; + return blkif; } @@ -472,12 +479,6 @@ static void xen_vbd_free(struct xen_vbd *vbd) vbd->bdev = NULL; } -/* Enable the persistent grants feature. */ -static bool feature_persistent = true; -module_param(feature_persistent, bool, 0644); -MODULE_PARM_DESC(feature_persistent, - "Enables the persistent grants feature"); - static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle, unsigned major, unsigned minor, int readonly, int cdrom) @@ -520,8 +521,6 @@ static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle, if (bdev_max_secure_erase_sectors(bdev)) vbd->discard_secure = true; - vbd->feature_gnt_persistent = feature_persistent; - pr_debug("Successful creation of handle=%04x (dom=%u)\n", handle, blkif->domid); return 0;