Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753515AbcD2NWS (ORCPT ); Fri, 29 Apr 2016 09:22:18 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:53510 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753321AbcD2NWP (ORCPT ); Fri, 29 Apr 2016 09:22:15 -0400 Subject: Re: VDSO unmap and remap support for additional architectures To: Andy Lutomirski , Catalin Marinas , criu@openvz.org, Dmitry Safonov , Will Deacon , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Arnd Bergmann , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, dsafonov@virtuozzo.com References: <20151202121918.GA4523@arm.com> <1461856737-17071-1-git-send-email-cov@codeaurora.org> <2ce7203f-305c-6edf-0ef9-448c141cb103@kernel.org> From: Christopher Covington Message-ID: <57236003.5060804@codeaurora.org> Date: Fri, 29 Apr 2016 09:22:11 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:43.0) Gecko/20100101 Thunderbird/43.0 MIME-Version: 1.0 In-Reply-To: <2ce7203f-305c-6edf-0ef9-448c141cb103@kernel.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2218 Lines: 60 Hi Andy, On 04/28/2016 02:53 PM, Andy Lutomirski wrote: > On 04/28/2016 08:18 AM, Christopher Covington wrote: >> Please take a look at the following prototype of sharing the PowerPC >> VDSO unmap and remap code with other architectures. I've only hooked >> up arm64 to begin with. If folks think this is a reasonable approach I >> can work on 32 bit ARM as well. Not hearing back from an earlier >> request for guidance [1], I simply dove in and started hacking. >> Laurent's test case [2][3] is a compelling illustration of whether VDSO >> remap works or not on a given architecture. > > I think there's a much nicer way: > > https://lkml.kernel.org/r/1461584223-9418-1-git-send-email-dsafonov@virtuozzo.com > > Could arm64 and ppc use this approach? These arch_xyz hooks are gross. Thanks for the pointer. Any thoughts on how to keep essentially identical definitions of vdso_mremap from proliferating into every architecture and variant? > Also, at some point, possibly quite soon, x86 will want a way for > user code to ask the kernel to map a specific vdso variant at a specific > address. Could we perhaps add a new pair of syscalls: > > struct vdso_info { > unsigned long space_needed_before; > unsigned long space_needed_after; > unsigned long alignment; > }; > > long vdso_get_info(unsigned int vdso_type, struct vdso_info *info); > > long vdso_remap(unsigned int vdso_type, unsigned long addr, unsigned int flags); > > #define VDSO_X86_I386 0 > #define VDSO_X86_64 1 > #define VDSO_X86_X32 2 > // etc. > > vdso_remap will map the vdso of the chosen type such at > AT_SYSINFO_EHDR lines up with addr. It will use up to > space_needed_before bytes before that address and space_needed_after > after than address. It will also unmap the old vdso (or maybe only do > that if some flag is set). > > On x86, mremap is *not* sufficient for everything that's needed, > because some programs will need to change the vdso type. I don't I understand. Why can't people just exec() the ELF type that corresponds to the VDSO they want? Thanks, Cov -- Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project