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=-4.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 EE000C433E6 for ; Tue, 14 Jul 2020 12:50:09 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A6E902242C for ; Tue, 14 Jul 2020 12:50:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A6E902242C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4B5gMy3QvwzDqfG for ; Tue, 14 Jul 2020 22:50:06 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=none (no SPF record) smtp.mailfrom=linux.intel.com (client-ip=134.134.136.20; helo=mga02.intel.com; envelope-from=jarkko.sakkinen@linux.intel.com; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4B5fXm4KLkzDqc4 for ; Tue, 14 Jul 2020 22:12:39 +1000 (AEST) IronPort-SDR: w0PWyNBPAvSCYP4LYbwDH0gx+YyTtJIBTA9ueEwcw227lT/4wHynAS9vUjfT0c8ZRgcWjVJSbi 3Rfsy4sIYIMw== X-IronPort-AV: E=McAfee;i="6000,8403,9681"; a="137016280" X-IronPort-AV: E=Sophos;i="5.75,350,1589266800"; d="scan'208";a="137016280" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Jul 2020 05:12:35 -0700 IronPort-SDR: gy5QgnmkOnvrE5FE0suJR8q17BCUDnIMq9U3Z/E6bO2L2CHcMBL7ozMWn6dB19fD/Uv6Qw8RhN QKqcw9ce1qhw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.75,350,1589266800"; d="scan'208";a="317697684" Received: from pipper-mobl1.ger.corp.intel.com (HELO localhost) ([10.249.46.185]) by fmsmga002.fm.intel.com with ESMTP; 14 Jul 2020 05:12:01 -0700 Date: Tue, 14 Jul 2020 15:11:59 +0300 From: Jarkko Sakkinen To: Russell King - ARM Linux admin Subject: Re: [PATCH 1/3] module: Rename module_alloc() to text_alloc() and move to kernel proper Message-ID: <20200714121159.GD1463346@linux.intel.com> References: <20200713182030.1418041-1-jarkko.sakkinen@linux.intel.com> <20200714095243.GB1442951@linux.intel.com> <20200714103333.GB1551@shell.armlinux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200714103333.GB1551@shell.armlinux.org.uk> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo X-Mailman-Approved-At: Tue, 14 Jul 2020 22:39:54 +1000 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Catalin Marinas , Kefeng Wang , Paul Mackerras , Zong Li , Andi Kleen , Paul Burton , Vincent Whitchurch , Petr Mladek , Brian Gerst , Andy Lutomirski , Yonghong Song , Thomas Gleixner , Jiri Kosina , Anup Patel , Linux Kernel Mailing List , Philipp Rudo , Torsten Duwe , Masami Hiramatsu , Andrew Morton , Mark Rutland , "James E.J. Bottomley" , Vincent Chen , "open list:S390" , Joe Lawrence , Helge Deller , John Fastabend , Anil S Keshavamurthy , Andrey Ryabinin , Iurii Zaikin , Andrii Nakryiko , Vasily Gorbik , "moderated list:ARM PORT" , Daniel Axtens , Damien Le Moal , Peter Oberparleiter , Sean Christopherson , Martin KaFai Lau , Song Liu , Paul Walmsley , Heiko Carstens , Alexei Starovoitov , Atish Patra , Will Deacon , Daniel Borkmann , Masahiro Yamada , Nayna Jain , Ley Foon Tan , Christian Borntraeger , Dmitry Vyukov , Sami Tolvanen , "Naveen N. Rao" , Mao Han , Marco Elver , Steven Rostedt , Babu Moger , Borislav Petkov , Greentime Hu , Ben Dooks , Guan Xuetao , Thomas Bogendoerfer , "open list:PARISC ARCHITECTURE" , Jessica Yu , "open list:BPF JIT for MIPS \(32-BIT AND 64-BIT\)" , "David S. Miller" , Thiago Jung Bauermann , Peter Zijlstra , "open list:SPARC + UltraSPARC \(sparc/sparc64\)" , Sandipan Das , "H. Peter Anvin" , Amit Daniel Kachhap , Tiezhu Yang , Miroslav Benes , Jiri Olsa , Ard Biesheuvel , Vincenzo Frascino , Anders Roxell , Sven Schnelle , "maintainer:X86 ARCHITECTURE \(32-BIT AND 64-BIT\)" , "open list:RISC-V ARCHITECTURE" , Mike Rapoport , Ingo Molnar , Albert Ou , "Paul E. McKenney" , Josh Poimboeuf , KP Singh , Gerald Schaefer , Nick Hu , "open list:BPF JIT for MIPS \(32-BIT AND 64-BIT\)" , "open list:MIPS" , Sergey Senozhatsky , Palmer Dabbelt , "open list:LINUX FOR POWERPC \(32-BIT AND 64-BIT\)" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, Jul 14, 2020 at 11:33:33AM +0100, Russell King - ARM Linux admin wrote: > On Tue, Jul 14, 2020 at 01:17:22PM +0300, Ard Biesheuvel wrote: > > On Tue, 14 Jul 2020 at 12:53, Jarkko Sakkinen > > wrote: > > > > > > On Mon, Jul 13, 2020 at 10:49:48PM +0300, Ard Biesheuvel wrote: > > > > This patch suggests that there are other reasons why conflating > > > > allocation of module space and allocating text pages for other uses > > > > is a bad idea, but switching all users to text_alloc() is a step in > > > > the wrong direction. It would be better to stop using module_alloc() > > > > in core code except in the module loader, and have a generic > > > > text_alloc() that can be overridden by the arch if necessary. Note > > > > that x86 and s390 are the only architectures that use module_alloc() > > > > in ftrace code. > > > > > > This series essentially does this: introduces text_alloc() and > > > text_memfree(), which have generic implementations in kernel/text.c. > > > Those can be overriddent by arch specific implementations. > > > > > > What you think should be done differently than in my patch set? > > > > > > > On arm64, module_alloc is only used by the module loader, and so > > pulling it out and renaming it will cause unused code to be > > incorporated into the kernel when building without module support, > > which is the use case you claim to be addressing. > > > > Module_alloc has semantics that are intimately tied to the module > > loader, but over the years, it ended up being (ab)used by other > > subsystems, which don't require those semantics but just need n pages > > of vmalloc space with executable permissions. > > > > So the correct approach is to make text_alloc() implement just that, > > generically, and switch bpf etc to use it. Then, only on architectures > > that need it, override it with an implementation that has the required > > additional semantics. > > > > Refactoring 10+ architectures like this without any regard for how > > text_alloc() deviates from module_alloc() just creates a lot of churn > > that others will have to clean up after you. > > For 32-bit ARM, our bpf code uses "blx/bx" (or equivalent code > sequences) rather than encoding a "bl" or "b", so BPF there doesn't > care where the executable memory is mapped, and doesn't need any > PLTs. Given that, should bpf always allocate from the vmalloc() > region to preserve the module space for modules? Most of the allocators use __vmalloc_node_range() but arch/nios2 uses just plain kmalloc(): /* * Modules should NOT be allocated with kmalloc for (obvious) reasons. * But we do it for now to avoid relocation issues. CALL26/PCREL26 cannot reach * from 0x80000000 (vmalloc area) to 0xc00000000 (kernel) (kmalloc returns * addresses in 0xc0000000) */ void *module_alloc(unsigned long size) { if (size == 0) return NULL; return kmalloc(size, GFP_KERNEL); } Also consider arch/x86 module_alloc(): void *module_alloc(unsigned long size) { void *p; if (PAGE_ALIGN(size) > MODULES_LEN) return NULL; p = __vmalloc_node_range(size, MODULE_ALIGN, MODULES_VADDR + get_module_load_offset(), MODULES_END, GFP_KERNEL, PAGE_KERNEL, 0, NUMA_NO_NODE, __builtin_return_address(0)); if (p && (kasan_module_alloc(p, size) < 0)) { vfree(p); return NULL; } return p; } The generic version is void * __weak module_alloc(unsigned long size) { return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END, GFP_KERNEL, PAGE_KERNEL_EXEC, VM_FLUSH_RESET_PERMS, NUMA_NO_NODE, __builtin_return_address(0)); } There is quite a lot of divergence from the generic version. However, in other arch's it's mostly just divergence in vmalloc() parameters and not as radical as in x86. I could probably limit the total havoc to just nios2 and x86 if there is a set of vmalloc parameters that work for all arch's. Then there could be kernel/text.c and re-implementations for x86 and nios2. I'm all for having separate text_alloc() and text_memfree() if these issues can be somehow sorted out. /Jarkko