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=-10.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 DAEE4C433E1 for ; Tue, 28 Jul 2020 08:17:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B83EF22B43 for ; Tue, 28 Jul 2020 08:17:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595924243; bh=3fxjXoDgSBiwnSHqXnV1f6LzXR3qMTb2G2BKx/anIjU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=TVbend5clDs12MmHwsYWDyq4KRAeuNsjZ2WFWD38raHbHL8VdzR5vm579MMuPKuOQ BTIBG/mGpljzoiRIn9FGY3iM4WN1VKCYcLkZOa8uih7sm22ngg3P1uDoV9OX5dT0sd 6N27VsrNp+SXn/cAfbhgDu5dcgYOjj2aRLkOxUz8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728053AbgG1IRW (ORCPT ); Tue, 28 Jul 2020 04:17:22 -0400 Received: from mail.kernel.org ([198.145.29.99]:47592 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727878AbgG1IRV (ORCPT ); Tue, 28 Jul 2020 04:17:21 -0400 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id CDF532177B; Tue, 28 Jul 2020 08:17:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595924240; bh=3fxjXoDgSBiwnSHqXnV1f6LzXR3qMTb2G2BKx/anIjU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=cP/1mWVhwzYFHuE/o20/ObrPDNBusuSlukT/jhE9M6CttC1iJo8RejcopDujlYEaX KjN5FmG9MSsoE/RMN1/treziZsdRTrxwbFKigPD7cgkc2nLa1Q7CQA/SlfTe5byDM7 83BQW/0C09K+ESYWg9I8N1wgw/6HjGWp5eawq+ek= Date: Tue, 28 Jul 2020 17:17:15 +0900 From: Masami Hiramatsu To: Ard Biesheuvel Cc: Mike Rapoport , Jarkko Sakkinen , Ingo Molnar , Linux Kernel Mailing List , linux-mm@kvack.org, Andi Kleen , Masami Hiramatsu , Peter Zijlstra , "Naveen N. Rao" , Anil S Keshavamurthy , "David S. Miller" , Jessica Yu Subject: Re: [PATCH v5 5/6] kprobes: Use text_alloc() and text_free() Message-Id: <20200728171715.0800093e2226e3d72b04a3ae@kernel.org> In-Reply-To: References: <20200724050553.1724168-1-jarkko.sakkinen@linux.intel.com> <20200724050553.1724168-6-jarkko.sakkinen@linux.intel.com> <20200724092746.GD517988@gmail.com> <20200725031648.GG17052@linux.intel.com> <20200726081408.GB2927915@kernel.org> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 26 Jul 2020 19:06:20 +0300 Ard Biesheuvel wrote: > On Sun, 26 Jul 2020 at 11:14, Mike Rapoport wrote: > > > > On Sat, Jul 25, 2020 at 06:16:48AM +0300, Jarkko Sakkinen wrote: > > > On Fri, Jul 24, 2020 at 11:27:46AM +0200, Ingo Molnar wrote: > > > > > > > > * Jarkko Sakkinen wrote: > > > > > > > > > Use text_alloc() and text_free() instead of module_alloc() and > > > > > module_memfree() when an arch provides them. > > > > > > > > > > Cc: linux-mm@kvack.org > > > > > Cc: Andi Kleen > > > > > Cc: Masami Hiramatsu > > > > > Cc: Peter Zijlstra > > > > > Signed-off-by: Jarkko Sakkinen > > > > > --- > > > > > kernel/kprobes.c | 9 +++++++++ > > > > > 1 file changed, 9 insertions(+) > > > > > > > > > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > > > > > index 4e46d96d4e16..611fcda9f6bf 100644 > > > > > --- a/kernel/kprobes.c > > > > > +++ b/kernel/kprobes.c > > > > > @@ -40,6 +40,7 @@ > > > > > #include > > > > > #include > > > > > #include > > > > > +#include > > > > > > > > > > #define KPROBE_HASH_BITS 6 > > > > > #define KPROBE_TABLE_SIZE (1 << KPROBE_HASH_BITS) > > > > > @@ -111,12 +112,20 @@ enum kprobe_slot_state { > > > > > > > > > > void __weak *alloc_insn_page(void) > > > > > { > > > > > +#ifdef CONFIG_ARCH_HAS_TEXT_ALLOC > > > > > + return text_alloc(PAGE_SIZE); > > > > > +#else > > > > > return module_alloc(PAGE_SIZE); > > > > > +#endif > > > > > } > > > > > > > > > > void __weak free_insn_page(void *page) > > > > > { > > > > > +#ifdef CONFIG_ARCH_HAS_TEXT_ALLOC > > > > > + text_free(page); > > > > > +#else > > > > > module_memfree(page); > > > > > +#endif > > > > > } > > > > > > > > I've read the observations in the other threads, but this #ifdef > > > > jungle is silly, it's a de-facto open coded text_alloc() with a > > > > module_alloc() fallback... > > > > > > In the previous version I had: > > > > > > https://lore.kernel.org/lkml/20200717030422.679972-4-jarkko.sakkinen@linux.intel.com/ > > > > > > and I had just calls to text_alloc() and text_free() in corresponding > > > snippet to the above. > > > > > > I got this feedback from Mike: > > > > > > https://lore.kernel.org/lkml/20200718162359.GA2919062@kernel.org/ > > > > > > I'm not still sure that I fully understand this feedback as I don't see > > > any inherent and obvious difference to the v4. In that version fallbacks > > > are to module_alloc() and module_memfree() and text_alloc() and > > > text_memfree() can be overridden by arch. > > > > Let me try to elaborate. > > > > There are several subsystems that need to allocate memory for executable > > text. As it happens, they use module_alloc() with some abilities for > > architectures to override this behaviour. > > > > For many architectures, it would be enough to rename modules_alloc() to > > text_alloc(), make it built-in and this way allow removing dependency on > > MODULES. > > > > Yet, some architectures have different restrictions for code allocation > > for different subsystems so it would make sense to have more than one > > variant of text_alloc() and a single config option ARCH_HAS_TEXT_ALLOC > > won't be sufficient. > > > > I liked Mark's suggestion to have text_alloc_() and proposed > > a way to introduce text_alloc_kprobes() along with > > HAVE_KPROBES_TEXT_ALLOC to enable arch overrides of this function. > > > > The major difference between your v4 and my suggestion is that I'm not > > trying to impose a single ARCH_HAS_TEXT_ALLOC as an alternative to > > MODULES but rather to use per subsystem config option, e.g. > > HAVE_KPROBES_TEXT_ALLOC. > > > > Another thing, which might be worth doing regardless of the outcome of > > this discussion is to rename alloc_insn_pages() to text_alloc_kprobes() > > because the former is way too generic and does not emphasize that the > > instruction page is actually used by kprobes only. The name of the insn_pages came from the struct kprobe_insn_page, so if there is a text_alloc_kprobe(), I'm OK to rename it. (anyway, that is an allocation operator, we don't call it directly.) > Masami or Peter should correct me if I am wrong, but it seems to me > that the way kprobes uses these pages does not require them to be in > relative branching range of the core kernel on any architecture, given > that they are populated with individual instruction opcodes that are > executed in single step mode, and relative branches are emulated (when > needed) Actually, x86 and arm has the "relative branching range" requirements for the jump optimized kprobes. For the other architectures, I think we don't need it. Only executable text buffer is needed. Thank you, > So for kprobes in particular, we should be able to come up with a > generic sequence that does not involve module_alloc(), and therefore > removes the kprobes dependency on module support entirely (with the > exception of power which maps the vmalloc space nx when module support > is disabled). Renaming alloc_insn_page() to something more descriptive > makes sense imo, but is a separate issue. -- Masami Hiramatsu