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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 1A081C433E1 for ; Tue, 23 Jun 2020 09:57:46 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D444420724 for ; Tue, 23 Jun 2020 09:57:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="EkrUXXkM" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D444420724 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 705F16B0002; Tue, 23 Jun 2020 05:57:45 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6B5776B0005; Tue, 23 Jun 2020 05:57:45 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 57DBA6B0006; Tue, 23 Jun 2020 05:57:45 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0056.hostedemail.com [216.40.44.56]) by kanga.kvack.org (Postfix) with ESMTP id 3C8566B0002 for ; Tue, 23 Jun 2020 05:57:45 -0400 (EDT) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id D3F838248047 for ; Tue, 23 Jun 2020 09:57:44 +0000 (UTC) X-FDA: 76960024848.20.doll26_50181c426e3a Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin20.hostedemail.com (Postfix) with ESMTP id A03C3180C0614 for ; Tue, 23 Jun 2020 09:57:44 +0000 (UTC) X-HE-Tag: doll26_50181c426e3a X-Filterd-Recvd-Size: 4638 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf11.hostedemail.com (Postfix) with ESMTP for ; Tue, 23 Jun 2020 09:57:44 +0000 (UTC) Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (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 2380020771; Tue, 23 Jun 2020 09:57:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592906263; bh=I6FXAd+dz0PTFAbZZ7Ggg1D9VAM+5cmaOuIX+WynUXY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=EkrUXXkMa7i2f43LSN2xaCpKDWrWjr9vOWsyZcdZfiB4wnJ0kZuDW76qe4YyJNbrA aEg23Q87gKOMdnDv8U0QvRrDTW7qWtqkVsfHY073/OprQW1G+a9vHKzgntu2AxnTod 889AuqDXeVGDQuPIkRG0Lyv7qEbtZ0eDRJML51+w= Date: Tue, 23 Jun 2020 10:57:38 +0100 From: Will Deacon To: Peter Zijlstra Cc: Christoph Hellwig , Andrew Morton , Dexuan Cui , Vitaly Kuznetsov , Catalin Marinas , Jessica Yu , x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 2/3] arm64: use PAGE_KERNEL_ROX directly in alloc_insn_page Message-ID: <20200623095737.GD3743@willie-the-truck> References: <20200618064307.32739-1-hch@lst.de> <20200618064307.32739-3-hch@lst.de> <20200620191616.bae356186ba3329ade67bbf7@linux-foundation.org> <20200623090505.GA7518@lst.de> <20200623090757.GB3743@willie-the-truck> <20200623093714.GE4781@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200623093714.GE4781@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) X-Rspamd-Queue-Id: A03C3180C0614 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 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, Jun 23, 2020 at 11:37:14AM +0200, Peter Zijlstra wrote: > On Tue, Jun 23, 2020 at 10:07:58AM +0100, Will Deacon wrote: > > On Tue, Jun 23, 2020 at 11:05:05AM +0200, Christoph Hellwig wrote: > > > On Sat, Jun 20, 2020 at 07:16:16PM -0700, Andrew Morton wrote: > > > > On Thu, 18 Jun 2020 08:43:06 +0200 Christoph Hellwig wrote: > > > > > --- a/arch/arm64/kernel/probes/kprobes.c > > > > > +++ b/arch/arm64/kernel/probes/kprobes.c > > > > > @@ -120,15 +120,9 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p) > > > > > > > > > > void *alloc_insn_page(void) > > > > > { > > > > > - void *page; > > > > > - > > > > > - page = vmalloc_exec(PAGE_SIZE); > > > > > - if (page) { > > > > > - set_memory_ro((unsigned long)page, 1); > > > > > - set_vm_flush_reset_perms(page); > > > > > - } > > > > > - > > > > > - return page; > > > > > + return __vmalloc_node_range(PAGE_SIZE, 1, VMALLOC_START, VMALLOC_END, > > > > > + GFP_KERNEL, PAGE_KERNEL_ROX, VM_FLUSH_RESET_PERMS, > > > > > + NUMA_NO_NODE, __func__); > > > > > } > > > > > > > > > > /* arm kprobe: install breakpoint in text */ > > > > > > > > But why. I think this is just a cleanup, doesn't address any runtime issue? > > > > > > It doesn't "fix" an issue - it just simplifies and speeds up the code. > > > > Ok, but I don't understand the PLT comment from Peter in > > 20200618092754.GF576905@hirez.programming.kicks-ass.net: > > > > | I think this has the exact same range issue as the x86 user. But it > > | might be less fatal if their PLT magic can cover the full range. > > > > Peter, please could you elaborate on your concern? I feel like I'm missing > > some context. > > On x86 we can only directly call code in a (signed) 32bit immediate > range (2G) and our kernel text and module range are constrained by that. > > IIRC ARM64 has an even smaller immediate range and needs to play fixup > games with trampolines or somesuch (there was an ARM specific name for > it that I've misplaced again). Does that machinery cover the entire > vmalloc space or are you only able to fix up for a smaller range? > > Your arch/arm64/kernel/module.c:module_alloc() implementation seems to > have an explicit module range different from the full vmalloc range, I'm > thinking this is for a reason. Ah, gotcha. In this case, we're talking about the kprobe out-of-line buffer. We don't directly branch to that; instead we take a BRK exception and either exception return + singlestep the OOL buffer, or we simulate the instruction if it's doing anything PC-relative, so I don't see the need for a PLT. Will