From nobody Tue Sep 9 17:41:22 2025 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 A0DC5C001B0 for ; Wed, 26 Jul 2023 16:54:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231925AbjGZQyP (ORCPT ); Wed, 26 Jul 2023 12:54:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38594 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231372AbjGZQyL (ORCPT ); Wed, 26 Jul 2023 12:54:11 -0400 Received: from out4-smtp.messagingengine.com (out4-smtp.messagingengine.com [66.111.4.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3D6692122; Wed, 26 Jul 2023 09:54:10 -0700 (PDT) Received: from compute5.internal (compute5.nyi.internal [10.202.2.45]) by mailout.nyi.internal (Postfix) with ESMTP id 8E4515C0198; Wed, 26 Jul 2023 12:54:09 -0400 (EDT) Received: from mailfrontend2 ([10.202.2.163]) by compute5.internal (MEProxy); Wed, 26 Jul 2023 12:54:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= invisiblethingslab.com; h=cc:cc:content-transfer-encoding :content-type:date:date:from:from:in-reply-to:in-reply-to :message-id:mime-version:references:reply-to:sender:subject :subject:to:to; s=fm3; t=1690390449; x=1690476849; bh=ZSGL4tfDeh 02pkZ94/2tVJRMmAk+Vt00ZLy1MQBP55Y=; b=pYszA4HxujdUCNeHbCaGgqeAQO 7OxCMPtp39OADgyPrJ6IGJ3WDJaUUCQkw8W4IeToBQ6U4npachIhLOcYUEccTkHl qwxZYsglorioRcl0KRpIUKpXyip8suW05TtFMYr1bMH+QKswOV4d9LwXFvry/Xqg 3oGtzYH6hzJsEQMNzoghVgTZbVv5cXGYVVBFzbpOnwwA/OILuUYNbEc0j8Efosv4 9uyrpqIPgliYk7JCXuYe8+oaUI3ZpqLm3gMS5amW6wQbBYkNgv2zKepmA9xW4uIA 9x7mlKYcI/Ut2b66V4Iyh7mb65OBOckVpOgTewFszt3A6YWEbnJnJU/utLfQ== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-transfer-encoding :content-type:date:date:feedback-id:feedback-id:from:from :in-reply-to:in-reply-to:message-id:mime-version:references :reply-to:sender:subject:subject:to:to:x-me-proxy:x-me-proxy :x-me-sender:x-me-sender:x-sasl-enc; s=fm3; t=1690390449; x= 1690476849; bh=ZSGL4tfDeh02pkZ94/2tVJRMmAk+Vt00ZLy1MQBP55Y=; b=p 6FSQOuj/2H3hSBngWtVOKyF58NPGfdIzkHe6K93sZ3hfbatPDPmekGd2XGMw5Ah9 3gW25iltNtEqN1Box5KAUKiZ+4MHJxflrNs/41tqdzMPmO60q3wmDwTTZnIdR5uw Vk+PPTPEHATApmQN8Tq/vdpvUx+nPf11G0pPsKRym/fJ2l3lZfg0ZqvGF6Z6XTtg NLxi/VAz3s8Tee8l05WxbQvqPPuhFYMWdHlV9MTNQZopu1SKZ9bUtPRTbFD1gHgn r02JTsH9aMaD+mBvaoJHFXdlcafXRZzBa9GPodVTznA88drZPOO/OidmXIJ4LxUM L4iUUdL27Um39/kAps+Qg== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedviedriedvgddutdehucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhephffvvefufffkofgjfhgggfestdekredtredttdenucfhrhhomhepffgvmhhi ucforghrihgvucfqsggvnhhouhhruceouggvmhhisehinhhvihhsihgslhgvthhhihhngh hslhgrsgdrtghomheqnecuggftrfgrthhtvghrnhepgefhffegieektedtgfffvdfhhfdt veeiieeuffduvdehieehjeekhfelieehkeelnecuffhomhgrihhnpehquhgsvghsqdhosh drohhrghenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepmhgrihhlfhhrohhm peguvghmihesihhnvhhishhisghlvghthhhinhhgshhlrggsrdgtohhm X-ME-Proxy: Feedback-ID: iac594737:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Wed, 26 Jul 2023 12:54:08 -0400 (EDT) From: Demi Marie Obenour To: Juergen Gross , Stefano Stabellini , Oleksandr Tyshchenko Cc: Demi Marie Obenour , Xen developer discussion , Linux Kernel Mailing List , stable@vger.kernel.org Subject: [PATCH v4] xen: speed up grant-table reclaim Date: Wed, 26 Jul 2023 12:52:41 -0400 Message-ID: <20230726165354.1252-1-demi@invisiblethingslab.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230627172216.1359-1-demi@invisiblethingslab.com> References: <20230627172216.1359-1-demi@invisiblethingslab.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" When a grant entry is still in use by the remote domain, Linux must put it on a deferred list. Normally, this list is very short, because the PV network and block protocols expect the backend to unmap the grant first. However, Qubes OS's GUI protocol is subject to the constraints of the X Window System, and as such winds up with the frontend unmapping the window first. As a result, the list can grow very large, resulting in a massive memory leak and eventual VM freeze. To partially solve this problem, make the number of entries that the VM will attempt to free at each iteration tunable. The default is still 10, but it can be overridden via a module parameter. This is Cc: stable because (when combined with appropriate userspace changes) it fixes a severe performance and stability problem for Qubes OS users. Cc: stable@vger.kernel.org Signed-off-by: Demi Marie Obenour Reviewed-by: Juergen Gross --- Documentation/ABI/testing/sysfs-module | 11 +++++++ drivers/xen/grant-table.c | 40 +++++++++++++++++++------- 2 files changed, 40 insertions(+), 11 deletions(-) Changes since v3: - do not mention Kconfig in the commit message. - add entry to Documentation/ABI for the new sysfs entry. Changes since v2: - use atomic_inc_return(x) and atomic_dec_return(x) instead of atomic_add_return(1, x) and atomic_sub_return(1, x) respectively. - move module_param macro closer to the definition of free_per_iteration. - add blank line between declarations and statements. Changes since v1: - drop setting default via Kconfig diff --git a/Documentation/ABI/testing/sysfs-module b/Documentation/ABI/tes= ting/sysfs-module index 08886367d0470e8d8922703a7d5174077801c2a8..62addab47d0c5908d26ec2f5d07= db5ce21833566 100644 --- a/Documentation/ABI/testing/sysfs-module +++ b/Documentation/ABI/testing/sysfs-module @@ -60,3 +60,14 @@ Description: Module taint flags: C staging driver module E unsigned module =3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +What: /sys/module/grant_table/parameters/free_per_iteration +Date: July 2023 +KernelVersion: 6.5 but backported to all supported stable branches +Contact: Xen developer discussion +Description: Read and write number of grant entries to attempt to free per= iteration. + + Note: Future versions of Xen and Linux may provide a better + interface for controlling the rate of deferred grant reclaim + or may not need it at all. +Users: Qubes OS (https://www.qubes-os.org) diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c index e1ec725c2819d4d5dede063eb00d86a6d52944c0..f13c3b76ad1eb7110e2a2981e9f= a4e504174e431 100644 --- a/drivers/xen/grant-table.c +++ b/drivers/xen/grant-table.c @@ -498,14 +498,21 @@ static LIST_HEAD(deferred_list); static void gnttab_handle_deferred(struct timer_list *); static DEFINE_TIMER(deferred_timer, gnttab_handle_deferred); =20 +static atomic64_t deferred_count; +static atomic64_t leaked_count; +static unsigned int free_per_iteration =3D 10; +module_param(free_per_iteration, uint, 0600); + static void gnttab_handle_deferred(struct timer_list *unused) { - unsigned int nr =3D 10; + unsigned int nr =3D READ_ONCE(free_per_iteration); + const bool ignore_limit =3D nr =3D=3D 0; struct deferred_entry *first =3D NULL; unsigned long flags; + size_t freed =3D 0; =20 spin_lock_irqsave(&gnttab_list_lock, flags); - while (nr--) { + while ((ignore_limit || nr--) && !list_empty(&deferred_list)) { struct deferred_entry *entry =3D list_first_entry(&deferred_list, struct deferred_entry, list); @@ -515,10 +522,14 @@ static void gnttab_handle_deferred(struct timer_list = *unused) list_del(&entry->list); spin_unlock_irqrestore(&gnttab_list_lock, flags); if (_gnttab_end_foreign_access_ref(entry->ref)) { + uint64_t ret =3D atomic64_dec_return(&deferred_count); + put_free_entry(entry->ref); - pr_debug("freeing g.e. %#x (pfn %#lx)\n", - entry->ref, page_to_pfn(entry->page)); + pr_debug("freeing g.e. %#x (pfn %#lx), %llu remaining\n", + entry->ref, page_to_pfn(entry->page), + (unsigned long long)ret); put_page(entry->page); + freed++; kfree(entry); entry =3D NULL; } else { @@ -530,21 +541,22 @@ static void gnttab_handle_deferred(struct timer_list = *unused) spin_lock_irqsave(&gnttab_list_lock, flags); if (entry) list_add_tail(&entry->list, &deferred_list); - else if (list_empty(&deferred_list)) - break; } - if (!list_empty(&deferred_list) && !timer_pending(&deferred_timer)) { + if (list_empty(&deferred_list)) + WARN_ON(atomic64_read(&deferred_count)); + else if (!timer_pending(&deferred_timer)) { deferred_timer.expires =3D jiffies + HZ; add_timer(&deferred_timer); } spin_unlock_irqrestore(&gnttab_list_lock, flags); + pr_debug("Freed %zu references", freed); } =20 static void gnttab_add_deferred(grant_ref_t ref, struct page *page) { struct deferred_entry *entry; gfp_t gfp =3D (in_atomic() || irqs_disabled()) ? GFP_ATOMIC : GFP_KERNEL; - const char *what =3D KERN_WARNING "leaking"; + uint64_t leaked, deferred; =20 entry =3D kmalloc(sizeof(*entry), gfp); if (!page) { @@ -567,10 +579,16 @@ static void gnttab_add_deferred(grant_ref_t ref, stru= ct page *page) add_timer(&deferred_timer); } spin_unlock_irqrestore(&gnttab_list_lock, flags); - what =3D KERN_DEBUG "deferring"; + deferred =3D atomic64_inc_return(&deferred_count); + leaked =3D atomic64_read(&leaked_count); + pr_debug("deferring g.e. %#x (pfn %#lx) (total deferred %llu, total leak= ed %llu)\n", + ref, page ? page_to_pfn(page) : -1, deferred, leaked); + } else { + deferred =3D atomic64_read(&deferred_count); + leaked =3D atomic64_inc_return(&leaked_count); + pr_warn("leaking g.e. %#x (pfn %#lx) (total deferred %llu, total leaked = %llu)\n", + ref, page ? page_to_pfn(page) : -1, deferred, leaked); } - printk("%s g.e. %#x (pfn %#lx)\n", - what, ref, page ? page_to_pfn(page) : -1); } =20 int gnttab_try_end_foreign_access(grant_ref_t ref) --=20 Sincerely, Demi Marie Obenour (she/her/hers) Invisible Things Lab