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 84C5DC19F2A for ; Thu, 11 Aug 2022 10:40:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234324AbiHKKk2 (ORCPT ); Thu, 11 Aug 2022 06:40:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46918 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233839AbiHKKk0 (ORCPT ); Thu, 11 Aug 2022 06:40:26 -0400 Received: from mail-pl1-x634.google.com (mail-pl1-x634.google.com [IPv6:2607:f8b0:4864:20::634]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 98DC830F53 for ; Thu, 11 Aug 2022 03:40:22 -0700 (PDT) Received: by mail-pl1-x634.google.com with SMTP id d16so16578019pll.11 for ; Thu, 11 Aug 2022 03:40:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc; bh=eGbXQsKb8yt2To4bDCbL2Z7QyRG8T1fC5MTNEkBLar0=; b=iUXron1LpIR8hrtUavxu3b9yUZKvnb030Kb9YJEVur5ODX7G3kCMK7hHRb+5CE5j4e qNCO+YrnCkl5eDB84ADA0UFgtoAFO27Zn2z44MIqzqKx6LatbdRdviXLRuSjn557aRwn 7rAX1F8NqjBSoLvXkCFoBbUyMYsgIDCJpXFVyCiouVUyNggAbnJbMZgW/ZFgSL8kCSqS oL7wpa+uyP+H4YMZeZp0JaufVmf6Dd6qcS5clnfezwA9Hy4pLSpbukFTVs3QyyWWjc01 5RJyXsCFKYnj/cfzrbZLSIe2QXPdtR7/lhpNLq3x4Ga00Kpwl45ohXKX73M5yonMPt11 A4BA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc; bh=eGbXQsKb8yt2To4bDCbL2Z7QyRG8T1fC5MTNEkBLar0=; b=wS1wmsMesDQgLiYURPbVQhJdd36jIyqYnb44YiCpLs+DZepMVRSvG2unj3x9l1vtiX j8UM0eHOc3P3obGfuf+5tOLIjE1G50sfDQr2TpvYSxRcQDThZ2z8g22NNsdr5BOTHv50 Ql40UD0ToKr4oCjW1Hpuydf9kRUjjZbEjEV1WsTP5CrTS/ZtlAdbEa/JdzWxz0tEx+it NhAk76bo2tHZDES63lZEVUhpICumXyozb2ePYxKnndhPem28yYGoxwtJ+UlntSo51mav 3RxN6bVHaK0++zIYDC71vhydVkzIhjhKiYnVFLHbPi3KiOyxR65KOdYKpetGU4MkL7BF At8A== X-Gm-Message-State: ACgBeo3U+jN7nXjJ7oZ63j9PjIeuQFBGD8qVLe91YzsFJEk9ayv/Jqnd w7lYq1P3vOT7QkgmMC3XM60= X-Google-Smtp-Source: AA6agR73mfxCoAqPIDjSSr9ENX+w797y+jQ/7NJs9mylmjnXYgBynDf220LcvxKAPJ9HcWz3Hph5tA== X-Received: by 2002:a17:90b:3e8c:b0:1f7:3792:d336 with SMTP id rj12-20020a17090b3e8c00b001f73792d336mr8325711pjb.0.1660214422056; Thu, 11 Aug 2022 03:40:22 -0700 (PDT) Received: from hyeyoo ([114.29.91.56]) by smtp.gmail.com with ESMTPSA id h11-20020a17090aa88b00b001f4fb21c11asm3402986pjq.21.2022.08.11.03.40.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Aug 2022 03:40:21 -0700 (PDT) Date: Thu, 11 Aug 2022 19:40:15 +0900 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> To: Imran Khan Cc: glider@google.com, elver@google.com, dvyukov@google.com, cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, vbabka@suse.cz, roman.gushchin@linux.dev, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-mm@kvack.org Subject: Re: [PATCH v2] Introduce sysfs interface to disable kfence for selected slabs. Message-ID: References: <20220811085938.2506536-1-imran.f.khan@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220811085938.2506536-1-imran.f.khan@oracle.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 11, 2022 at 06:59:38PM +1000, Imran Khan wrote: > By default kfence allocation can happen for any slab object, whose size > is up to PAGE_SIZE, as long as that allocation is the first allocation > after expiration of kfence sample interval. But in certain debugging > scenarios we may be interested in debugging corruptions involving > some specific slub objects like dentry or ext4_* etc. In such cases > limiting kfence for allocations involving only specific slub objects > will increase the probablity of catching the issue since kfence pool > will not be consumed by other slab objects. > > This patch introduces a sysfs interface '/sys/kernel/slab//skip_kfence' > to disable kfence for specific slabs. Having the interface work in this > way does not impact current/default behavior of kfence and allows us to > use kfence for specific slabs (when needed) as well. The decision to > skip/use kfence is taken depending on whether kmem_cache.flags has > (newly introduced) SLAB_SKIP_KFENCE flag set or not. > > Signed-off-by: Imran Khan > --- > > Changes since v1: > - Remove RFC tag > > include/linux/slab.h | 6 ++++++ > mm/kfence/core.c | 7 +++++++ > mm/slub.c | 27 +++++++++++++++++++++++++++ > 3 files changed, 40 insertions(+) > > diff --git a/include/linux/slab.h b/include/linux/slab.h > index 0fefdf528e0d..947d912fd08c 100644 > --- a/include/linux/slab.h > +++ b/include/linux/slab.h > @@ -119,6 +119,12 @@ > */ > #define SLAB_NO_USER_FLAGS ((slab_flags_t __force)0x10000000U) > > +#ifdef CONFIG_KFENCE > +#define SLAB_SKIP_KFENCE ((slab_flags_t __force)0x20000000U) > +#else > +#define SLAB_SKIP_KFENCE 0 > +#endif > + > /* The following flags affect the page allocator grouping pages by mobility */ > /* Objects are reclaimable */ > #define SLAB_RECLAIM_ACCOUNT ((slab_flags_t __force)0x00020000U) > diff --git a/mm/kfence/core.c b/mm/kfence/core.c > index c252081b11df..8c08ae2101d7 100644 > --- a/mm/kfence/core.c > +++ b/mm/kfence/core.c > @@ -1003,6 +1003,13 @@ void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags) > return NULL; > } > > + /* > + * Skip allocations for this slab, if KFENCE has been disabled for > + * this slab. > + */ > + if (s->flags & SLAB_SKIP_KFENCE) > + return NULL; > + > if (atomic_inc_return(&kfence_allocation_gate) > 1) > return NULL; > #ifdef CONFIG_KFENCE_STATIC_KEYS > diff --git a/mm/slub.c b/mm/slub.c > index 862dbd9af4f5..ee8b48327536 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -5745,6 +5745,30 @@ STAT_ATTR(CPU_PARTIAL_NODE, cpu_partial_node); > STAT_ATTR(CPU_PARTIAL_DRAIN, cpu_partial_drain); > #endif /* CONFIG_SLUB_STATS */ > > +#ifdef CONFIG_KFENCE > +static ssize_t skip_kfence_show(struct kmem_cache *s, char *buf) > +{ > + return sysfs_emit(buf, "%d\n", !!(s->flags & SLAB_SKIP_KFENCE)); > +} > + > +static ssize_t skip_kfence_store(struct kmem_cache *s, > + const char *buf, size_t length) > +{ > + int ret = length; > + > + if (buf[0] == '0') > + s->flags &= ~SLAB_SKIP_KFENCE; > + else if (buf[0] == '1') > + s->flags |= SLAB_SKIP_KFENCE; > + else > + ret = -EINVAL; > + > + return ret; > +} > +SLAB_ATTR(skip_kfence); > + > +#endif > + > static struct attribute *slab_attrs[] = { > &slab_size_attr.attr, > &object_size_attr.attr, > @@ -5812,6 +5836,9 @@ static struct attribute *slab_attrs[] = { > &failslab_attr.attr, > #endif > &usersize_attr.attr, > +#ifdef CONFIG_KFENCE > + &skip_kfence_attr.attr, > +#endif > > NULL > }; > > base-commit: 40d43a7507e1547dd45cb02af2e40d897c591870 > -- > 2.30.2 No strong opinion on its interface, but from view of correctness: Looks good to me. Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> -- Thanks, Hyeonggon