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=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, 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 BAB2AC433E8 for ; Tue, 28 Jul 2020 10:56:58 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7B13820829 for ; Tue, 28 Jul 2020 10:56:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="JWZMBJ83" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7B13820829 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 0B6658D000B; Tue, 28 Jul 2020 06:56:58 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0666F8D0005; Tue, 28 Jul 2020 06:56:58 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E706C8D000B; Tue, 28 Jul 2020 06:56:57 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0177.hostedemail.com [216.40.44.177]) by kanga.kvack.org (Postfix) with ESMTP id D09E28D0005 for ; Tue, 28 Jul 2020 06:56:57 -0400 (EDT) Received: from smtpin10.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 8E191180AD817 for ; Tue, 28 Jul 2020 10:56:57 +0000 (UTC) X-FDA: 77087182074.10.horse70_5c06fd426f69 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin10.hostedemail.com (Postfix) with ESMTP id 5C4D416A0AB for ; Tue, 28 Jul 2020 10:56:57 +0000 (UTC) X-HE-Tag: horse70_5c06fd426f69 X-Filterd-Recvd-Size: 8425 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf50.hostedemail.com (Postfix) with ESMTP for ; Tue, 28 Jul 2020 10:56:56 +0000 (UTC) Received: from mail-ot1-f44.google.com (mail-ot1-f44.google.com [209.85.210.44]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B910A204EA for ; Tue, 28 Jul 2020 10:56:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595933815; bh=FgcTnYXgA0rEllPu4tLOBKhCeVE/MwrCLcbdciPSbZY=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=JWZMBJ83jcH+bMosW6PNvkNvoWQPeb7JhsUAcIsXH0RZeNllMlPJT1xMLvgmjTKPp vUm6eCWf+sHFJ3LKfsBi4FI6OX2BHOaj8nhfqe2CxFJR1ERRt0Km/1EDolfGIxGQla Qv2zNsS8W/alO3sphsiOVCTdgD560qEw8lMxAVG0= Received: by mail-ot1-f44.google.com with SMTP id w17so14575338otl.4 for ; Tue, 28 Jul 2020 03:56:55 -0700 (PDT) X-Gm-Message-State: AOAM531AKNZxq0YcWe4mhAYYMQ2k17d98jLcBRl6XAasnh12Ou/4x9EA f0Ts9kX5KhA3fRtRyOFfFjgZwUufAkv7PbUQiBE= X-Google-Smtp-Source: ABdhPJxsfIEG3PipIScO0TY7NQcbqjqsDYShQhVLbQymjWiMKVdLOw1doMOSzbAJxKAyUboo7j0mFL1lx5xjSiClMhU= X-Received: by 2002:a9d:3a04:: with SMTP id j4mr10807490otc.108.1595933815109; Tue, 28 Jul 2020 03:56:55 -0700 (PDT) MIME-Version: 1.0 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> <20200728171715.0800093e2226e3d72b04a3ae@kernel.org> In-Reply-To: <20200728171715.0800093e2226e3d72b04a3ae@kernel.org> From: Ard Biesheuvel Date: Tue, 28 Jul 2020 13:56:43 +0300 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v5 5/6] kprobes: Use text_alloc() and text_free() To: Masami Hiramatsu Cc: Mike Rapoport , Jarkko Sakkinen , Ingo Molnar , Linux Kernel Mailing List , linux-mm@kvack.org, Andi Kleen , Peter Zijlstra , "Naveen N. Rao" , Anil S Keshavamurthy , "David S. Miller" , Jessica Yu Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 5C4D416A0AB X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, 28 Jul 2020 at 11:17, Masami Hiramatsu wrote: > > 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. > Thanks for the explanation. Today, arm64 uses the definition below. void *alloc_insn_page(void) { return __vmalloc_node_range(PAGE_SIZE, 1, VMALLOC_START, VMALLOC_END, GFP_KERNEL, PAGE_KERNEL_ROX, VM_FLUSH_RESET_PERMS, NUMA_NO_NODE, __builtin_return_address(0)); } Do you think we could use that as the generic implementation if we use MODULES_START/_END as the allocation window?