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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A885FC433F5 for ; Thu, 10 Mar 2022 03:31:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232408AbiCJDcg (ORCPT ); Wed, 9 Mar 2022 22:32:36 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40676 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231621AbiCJDcf (ORCPT ); Wed, 9 Mar 2022 22:32:35 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DB88112A74A for ; Wed, 9 Mar 2022 19:31:35 -0800 (PST) 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 dfw.source.kernel.org (Postfix) with ESMTPS id 6DA9261787 for ; Thu, 10 Mar 2022 03:31:35 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BC4AAC340EB; Thu, 10 Mar 2022 03:31:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1646883094; bh=j5TWWjtHrmFTZBsFSC9ttsD5zGLBE0kzNFt1+RY1+Bg=; h=Date:To:From:Subject:From; b=T0BRYQ0C7A0lXhB3zrDH+rEG0ZP9pi2bk1OKpL7D3KIQoM5ZyCqVlSsqoHOYqiCUj 4QtjdBUeZ2aRYN5NSdGH78ekOLzmdP7OB+AY931zGaiZR0QHDSyOaEPlDkhuFkwMxt 7P6rgaLZ+AX4acJNIfDkZEMegNWAuGBrvUwNLJIk= Date: Wed, 09 Mar 2022 19:31:34 -0800 To: mm-commits@vger.kernel.org, glider@google.com, dvyukov@google.com, elver@google.com, akpm@linux-foundation.org From: Andrew Morton Subject: + kfence-allow-use-of-a-deferrable-timer.patch added to -mm tree Message-Id: <20220310033134.BC4AAC340EB@smtp.kernel.org> Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org The patch titled Subject: kfence: allow use of a deferrable timer has been added to the -mm tree. Its filename is kfence-allow-use-of-a-deferrable-timer.patch This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/kfence-allow-use-of-a-deferrable-timer.patch and later at https://ozlabs.org/~akpm/mmotm/broken-out/kfence-allow-use-of-a-deferrable-timer.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Marco Elver Subject: kfence: allow use of a deferrable timer Allow the use of a deferrable timer, which does not force CPU wake-ups when the system is idle. A consequence is that the sample interval becomes very unpredictable, to the point that it is not guaranteed that the KFENCE KUnit test still passes. Nevertheless, on power-constrained systems this may be preferable, so let's give the user the option should they accept the above trade-off. Link: https://lkml.kernel.org/r/20220308141415.3168078-1-elver@google.com Signed-off-by: Marco Elver Reviewed-by: Alexander Potapenko Cc: Dmitry Vyukov Signed-off-by: Andrew Morton --- Documentation/dev-tools/kfence.rst | 12 ++++++++++++ lib/Kconfig.kfence | 12 ++++++++++++ mm/kfence/core.c | 15 +++++++++++++-- 3 files changed, 37 insertions(+), 2 deletions(-) --- a/Documentation/dev-tools/kfence.rst~kfence-allow-use-of-a-deferrable-timer +++ a/Documentation/dev-tools/kfence.rst @@ -41,6 +41,18 @@ guarded by KFENCE. The default is config ``CONFIG_KFENCE_SAMPLE_INTERVAL``. Setting ``kfence.sample_interval=0`` disables KFENCE. +The sample interval controls a timer that sets up KFENCE allocations. By +default, to keep the real sample interval predictable, the normal timer also +causes CPU wake-ups when the system is completely idle. This may be undesirable +on power-constrained systems. The boot parameter ``kfence.deferrable=1`` +instead switches to a "deferrable" timer which does not force CPU wake-ups on +idle systems, at the risk of unpredictable sample intervals. The default is +configurable via the Kconfig option ``CONFIG_KFENCE_DEFERRABLE``. + +.. warning:: + The KUnit test suite is very likely to fail when using a deferrable timer + since it currently causes very unpredictable sample intervals. + The KFENCE memory pool is of fixed size, and if the pool is exhausted, no further KFENCE allocations occur. With ``CONFIG_KFENCE_NUM_OBJECTS`` (default 255), the number of available guarded objects can be controlled. Each object --- a/lib/Kconfig.kfence~kfence-allow-use-of-a-deferrable-timer +++ a/lib/Kconfig.kfence @@ -45,6 +45,18 @@ config KFENCE_NUM_OBJECTS pages are required; with one containing the object and two adjacent ones used as guard pages. +config KFENCE_DEFERRABLE + bool "Use a deferrable timer to trigger allocations" + help + Use a deferrable timer to trigger allocations. This avoids forcing + CPU wake-ups if the system is idle, at the risk of a less predictable + sample interval. + + Warning: The KUnit test suite fails with this option enabled - due to + the unpredictability of the sample interval! + + Say N if you are unsure. + config KFENCE_STATIC_KEYS bool "Use static keys to set up allocations" if EXPERT depends on JUMP_LABEL --- a/mm/kfence/core.c~kfence-allow-use-of-a-deferrable-timer +++ a/mm/kfence/core.c @@ -95,6 +95,10 @@ module_param_cb(sample_interval, &sample static unsigned long kfence_skip_covered_thresh __read_mostly = 75; module_param_named(skip_covered_thresh, kfence_skip_covered_thresh, ulong, 0644); +/* If true, use a deferrable timer. */ +static bool kfence_deferrable __read_mostly = IS_ENABLED(CONFIG_KFENCE_DEFERRABLE); +module_param_named(deferrable, kfence_deferrable, bool, 0444); + /* The pool of pages used for guard pages and objects. */ char *__kfence_pool __read_mostly; EXPORT_SYMBOL(__kfence_pool); /* Export for test modules. */ @@ -740,6 +744,8 @@ late_initcall(kfence_debugfs_init); /* === Allocation Gate Timer ================================================ */ +static struct delayed_work kfence_timer; + #ifdef CONFIG_KFENCE_STATIC_KEYS /* Wait queue to wake up allocation-gate timer task. */ static DECLARE_WAIT_QUEUE_HEAD(allocation_wait); @@ -762,7 +768,6 @@ static DEFINE_IRQ_WORK(wake_up_kfence_ti * avoids IPIs, at the cost of not immediately capturing allocations if the * instructions remain cached. */ -static struct delayed_work kfence_timer; static void toggle_allocation_gate(struct work_struct *work) { if (!READ_ONCE(kfence_enabled)) @@ -790,7 +795,6 @@ static void toggle_allocation_gate(struc queue_delayed_work(system_unbound_wq, &kfence_timer, msecs_to_jiffies(kfence_sample_interval)); } -static DECLARE_DELAYED_WORK(kfence_timer, toggle_allocation_gate); /* === Public interface ===================================================== */ @@ -809,8 +813,15 @@ static void kfence_init_enable(void) { if (!IS_ENABLED(CONFIG_KFENCE_STATIC_KEYS)) static_branch_enable(&kfence_allocation_key); + + if (kfence_deferrable) + INIT_DEFERRABLE_WORK(&kfence_timer, toggle_allocation_gate); + else + INIT_DELAYED_WORK(&kfence_timer, toggle_allocation_gate); + WRITE_ONCE(kfence_enabled, true); queue_delayed_work(system_unbound_wq, &kfence_timer, 0); + pr_info("initialized - using %lu bytes for %d objects at 0x%p-0x%p\n", KFENCE_POOL_SIZE, CONFIG_KFENCE_NUM_OBJECTS, (void *)__kfence_pool, (void *)(__kfence_pool + KFENCE_POOL_SIZE)); _ Patches currently in -mm which might be from elver@google.com are kfence-allow-use-of-a-deferrable-timer.patch revert-ubsan-kcsan-dont-combine-sanitizer-with-kcov-on-clang.patch