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=-19.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 246CBC433E9 for ; Tue, 5 Jan 2021 11:03:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CDAFD229F0 for ; Tue, 5 Jan 2021 11:03:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729442AbhAELDF (ORCPT ); Tue, 5 Jan 2021 06:03:05 -0500 Received: from smtp-fw-9102.amazon.com ([207.171.184.29]:33301 "EHLO smtp-fw-9102.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729428AbhAELDB (ORCPT ); Tue, 5 Jan 2021 06:03:01 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1609844581; x=1641380581; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version; bh=cfpUF7JwdVlg9OD5nYIVIEb0EXDerqi+uCFKZFK8Hsw=; b=ln3cDlw7e9Jmx9uBuhyAvYV4PZoBQGl9uxA0rXyZ35NepUyutxCFysS1 tU9kkN6PTYt1Ipe+2Wv/X+9Y9KQMXv93YkSjOoxEgTShwz99sjxoJTZIq 7KctVd4ZOSCiLETpJbAesvY5qVHL8us+h3KEyw2nIqSWfl8xP3pjwH1tH U=; X-IronPort-AV: E=Sophos;i="5.78,476,1599523200"; d="scan'208";a="109582029" Received: from sea32-co-svc-lb4-vlan3.sea.corp.amazon.com (HELO email-inbound-relay-2a-d0be17ee.us-west-2.amazon.com) ([10.47.23.38]) by smtp-border-fw-out-9102.sea19.amazon.com with ESMTP; 05 Jan 2021 11:02:14 +0000 Received: from EX13D31EUA001.ant.amazon.com (pdx1-ws-svc-p6-lb9-vlan3.pdx.amazon.com [10.236.137.198]) by email-inbound-relay-2a-d0be17ee.us-west-2.amazon.com (Postfix) with ESMTPS id 66049A20ED; Tue, 5 Jan 2021 11:02:13 +0000 (UTC) Received: from u3f2cd687b01c55.ant.amazon.com (10.43.162.94) by EX13D31EUA001.ant.amazon.com (10.43.165.15) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Tue, 5 Jan 2021 11:02:08 +0000 From: SeongJae Park To: CC: SeongJae Park , , , , , , , Subject: [PATCH 1/5] xen/xenbus: Allow watches discard events before queueing Date: Tue, 5 Jan 2021 12:01:38 +0100 Message-ID: <20210105110142.1810-2-sjpark@amazon.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20210105110142.1810-1-sjpark@amazon.com> References: <20210105110142.1810-1-sjpark@amazon.com> MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.43.162.94] X-ClientProxiedBy: EX13D45UWA001.ant.amazon.com (10.43.160.91) To EX13D31EUA001.ant.amazon.com (10.43.165.15) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: SeongJae Park If handling logics of watch events are slower than the events enqueue logic and the events can be created from the guests, the guests could trigger memory pressure by intensively inducing the events, because it will create a huge number of pending events that exhausting the memory. This is known as XSA-349. Fortunately, some watch events could be ignored, depending on its handler callback. For example, if the callback has interest in only one single path, the watch wouldn't want multiple pending events. Or, some watches could ignore events to same path. To let such watches to volutarily help avoiding the memory pressure situation, this commit introduces new watch callback, 'will_handle'. If it is not NULL, it will be called for each new event just before enqueuing it. Then, if the callback returns false, the event will be discarded. No watch is using the callback for now, though. This is part of XSA-349 This is upstream commit fed1755b118147721f2c87b37b9d66e62c39b668 Cc: stable@vger.kernel.org Signed-off-by: SeongJae Park Reported-by: Michael Kurth Reported-by: Pawel Wieczorkiewicz Reviewed-by: Juergen Gross Signed-off-by: Juergen Gross --- drivers/net/xen-netback/xenbus.c | 2 ++ drivers/xen/xenbus/xenbus_client.c | 1 + drivers/xen/xenbus/xenbus_xs.c | 7 ++++++- include/xen/xenbus.h | 7 +++++++ 4 files changed, 16 insertions(+), 1 deletion(-) diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c index b44f37fff890..5cb9dbf62816 100644 --- a/drivers/net/xen-netback/xenbus.c +++ b/drivers/net/xen-netback/xenbus.c @@ -770,12 +770,14 @@ static int xen_register_credit_watch(struct xenbus_device *dev, return -ENOMEM; snprintf(node, maxlen, "%s/rate", dev->nodename); vif->credit_watch.node = node; + vif->credit_watch.will_handle = NULL; vif->credit_watch.callback = xen_net_rate_changed; err = register_xenbus_watch(&vif->credit_watch); if (err) { pr_err("Failed to set watcher %s\n", vif->credit_watch.node); kfree(node); vif->credit_watch.node = NULL; + vif->credit_watch.will_handle = NULL; vif->credit_watch.callback = NULL; } return err; diff --git a/drivers/xen/xenbus/xenbus_client.c b/drivers/xen/xenbus/xenbus_client.c index 266f446ba331..d02d25f784c9 100644 --- a/drivers/xen/xenbus/xenbus_client.c +++ b/drivers/xen/xenbus/xenbus_client.c @@ -120,6 +120,7 @@ int xenbus_watch_path(struct xenbus_device *dev, const char *path, int err; watch->node = path; + watch->will_handle = NULL; watch->callback = callback; err = register_xenbus_watch(watch); diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c index 22f7cd711c57..d200aa707988 100644 --- a/drivers/xen/xenbus/xenbus_xs.c +++ b/drivers/xen/xenbus/xenbus_xs.c @@ -901,7 +901,12 @@ static int process_msg(void) spin_lock(&watches_lock); msg->u.watch.handle = find_watch( msg->u.watch.vec[XS_WATCH_TOKEN]); - if (msg->u.watch.handle != NULL) { + if (msg->u.watch.handle != NULL && + (!msg->u.watch.handle->will_handle || + msg->u.watch.handle->will_handle( + msg->u.watch.handle, + (const char **)msg->u.watch.vec, + msg->u.watch.vec_size))) { spin_lock(&watch_events_lock); list_add_tail(&msg->list, &watch_events); wake_up(&watch_events_waitq); diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h index 32b944b7cebd..11697aa023b5 100644 --- a/include/xen/xenbus.h +++ b/include/xen/xenbus.h @@ -58,6 +58,13 @@ struct xenbus_watch /* Path being watched. */ const char *node; + /* + * Called just before enqueing new event while a spinlock is held. + * The event will be discarded if this callback returns false. + */ + bool (*will_handle)(struct xenbus_watch *, + const char **vec, unsigned int len); + /* Callback (executed in a process context with no locks held). */ void (*callback)(struct xenbus_watch *, const char **vec, unsigned int len); -- 2.17.1