From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx139.postini.com [74.125.245.139]) by kanga.kvack.org (Postfix) with SMTP id 6FE866B0088 for ; Tue, 20 Nov 2012 05:40:59 -0500 (EST) Received: by mail-bk0-f41.google.com with SMTP id jg9so2739300bkc.14 for ; Tue, 20 Nov 2012 02:40:57 -0800 (PST) Date: Tue, 20 Nov 2012 11:40:53 +0100 From: Ingo Molnar Subject: Re: [PATCH 00/27] Latest numa/core release, v16 Message-ID: <20121120104053.GA15302@gmail.com> References: <1353291284-2998-1-git-send-email-mingo@kernel.org> <20121119162909.GL8218@suse.de> <20121119191339.GA11701@gmail.com> <20121119211804.GM8218@suse.de> <20121119223604.GA13470@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121119223604.GA13470@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Peter Zijlstra , Paul Turner , Lee Schermerhorn , Christoph Lameter , Rik van Riel , Andrew Morton , Andrea Arcangeli , Linus Torvalds , Thomas Gleixner , Johannes Weiner , Hugh Dickins btw., mind sending me a fuller/longer profile than the one you've sent before? In particular does your system have any vsyscall emulation page fault overhead? If yes, does the patch below change anything for you? Thanks, Ingo ----------------> Subject: x86/vsyscall: Add Kconfig option to use native vsyscalls, switch to it From: Ingo Molnar Apparently there's still plenty of systems out there triggering the vsyscall emulation page faults - causing hard to track down performance regressions on page fault intense workloads... Some people seem to have run into that with threading-intense Java workloads. So until there's a better solution to this, add a Kconfig switch to make the vsyscall mode configurable and turn native vsyscall support back on by default. Distributions whose libraries and applications use the vDSO and never access the vsyscall page can change the config option to off. Note, I don't think we want to expose the "none" option via a Kconfig switch - it breaks the ABI. So it's "native" versus "emulate", with "none" being available as a kernel boot option, for the super paranoid. For more background, see these upstream commits: 3ae36655b97a x86-64: Rework vsyscall emulation and add vsyscall= parameter 5cec93c216db x86-64: Emulate legacy vsyscalls Cc: Andy Lutomirski Cc: Linus Torvalds Signed-off-by: Ingo Molnar --- arch/x86/Kconfig | 21 +++++++++++++++++++++ arch/x86/kernel/vsyscall_64.c | 8 +++++++- 2 files changed, 28 insertions(+), 1 deletion(-) Index: linux/arch/x86/Kconfig =================================================================== --- linux.orig/arch/x86/Kconfig +++ linux/arch/x86/Kconfig @@ -2234,6 +2234,27 @@ config X86_X32 elf32_x86_64 support enabled to compile a kernel with this option set. +config X86_VSYSCALL_COMPAT + bool "vsyscall compatibility" + default y + help + vsyscalls, as global executable pages, can be a security hole + escallation helper by exposing an easy shell code target with + a predictable address. + + Many versions of glibc rely on the vsyscall page though, so it + cannot be eliminated unconditionally. If you disable this + option these systems will still work but might incur the overhead + of vsyscall emulation page faults. + + The vsyscall=none, vsyscall=emulate, vsyscall=native kernel boot + option can be used to override this mode as well. + + Keeping this option enabled leaves the vsyscall page enabled, + i.e. vsyscall=native. Disabling this option means vsyscall=emulate. + + If unsure, say Y. + config COMPAT def_bool y depends on IA32_EMULATION || X86_X32 Index: linux/arch/x86/kernel/vsyscall_64.c =================================================================== --- linux.orig/arch/x86/kernel/vsyscall_64.c +++ linux/arch/x86/kernel/vsyscall_64.c @@ -56,7 +56,13 @@ DEFINE_VVAR(int, vgetcpu_mode); DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data); -static enum { EMULATE, NATIVE, NONE } vsyscall_mode = EMULATE; +static enum { EMULATE, NATIVE, NONE } vsyscall_mode = +#ifdef CONFIG_X86_VSYSCALL_COMPAT + NATIVE +#else + EMULATE +#endif +; static int __init vsyscall_setup(char *str) { -- 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