From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id 3ADD36B0005 for ; Thu, 28 Apr 2016 14:53:26 -0400 (EDT) Received: by mail-pf0-f199.google.com with SMTP id e190so180820753pfe.3 for ; Thu, 28 Apr 2016 11:53:26 -0700 (PDT) Received: from mail.kernel.org (mail.kernel.org. [198.145.29.136]) by mx.google.com with ESMTPS id w127si11544495pfb.38.2016.04.28.11.53.25 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 28 Apr 2016 11:53:25 -0700 (PDT) Subject: Re: VDSO unmap and remap support for additional architectures References: <20151202121918.GA4523@arm.com> <1461856737-17071-1-git-send-email-cov@codeaurora.org> From: Andy Lutomirski Message-ID: <2ce7203f-305c-6edf-0ef9-448c141cb103@kernel.org> Date: Thu, 28 Apr 2016 11:53:22 -0700 MIME-Version: 1.0 In-Reply-To: <1461856737-17071-1-git-send-email-cov@codeaurora.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Christopher Covington , Catalin Marinas , criu@openvz.org, Laurent Dufour , 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 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. 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. --Andy -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org