From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id 3EFA16B0261 for ; Wed, 1 Nov 2017 18:14:17 -0400 (EDT) Received: by mail-pf0-f200.google.com with SMTP id v78so3302679pfk.8 for ; Wed, 01 Nov 2017 15:14:17 -0700 (PDT) Received: from mga06.intel.com (mga06.intel.com. [134.134.136.31]) by mx.google.com with ESMTPS id q15si677497pli.661.2017.11.01.15.14.16 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 01 Nov 2017 15:14:16 -0700 (PDT) Subject: Re: [PATCH 00/23] KAISER: unmap most of the kernel from userspace page tables References: <20171031223146.6B47C861@viggo.jf.intel.com> <20171101085424.cwvc4nrrdhvjc3su@gmail.com> From: Dave Hansen Message-ID: Date: Wed, 1 Nov 2017 15:14:11 -0700 MIME-Version: 1.0 In-Reply-To: <20171101085424.cwvc4nrrdhvjc3su@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Ingo Molnar Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andy Lutomirski , Linus Torvalds , Thomas Gleixner , Peter Zijlstra , "H. Peter Anvin" , borisBrian Gerst , Denys Vlasenko , Josh Poimboeuf , Thomas Garnier , Kees Cook On 11/01/2017 01:54 AM, Ingo Molnar wrote: > Beyond the inevitable cavalcade of (solvable) problems that will pop up during > review, one major item I'd like to see addressed is runtime configurability: it > should be possible to switch between a CR3-flushing and a regular syscall and page > table model on the admin level, without restarting the kernel and apps. Distros > really, really don't want to double the number of kernel variants they have. > > The 'Kaiser off' runtime switch doesn't have to be as efficient as > CONFIG_KAISER=n, at least initialloy, but at minimum it should avoid the most > expensive page table switching paths in the syscall entry codepaths. Due to popular demand, I went and implemented this today. It's not the prettiest code I ever wrote, but it's pretty small. Just in case anyone wants to play with it, I threw a snapshot of it up here: > https://git.kernel.org/pub/scm/linux/kernel/git/daveh/x86-kaiser.git/log/?h=kaiser-dynamic-414rc6-20171101 I ran some quick tests. When CONFIG_KAISER=y, but "echo 0 > kaiser-enabled", the tests that I ran were within the noise vs. a vanilla kernel, and that's with *zero* optimization. -- 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