Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933953AbbDWWcT (ORCPT ); Thu, 23 Apr 2015 18:32:19 -0400 Received: from terminus.zytor.com ([198.137.202.10]:58451 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932410AbbDWWcR (ORCPT ); Thu, 23 Apr 2015 18:32:17 -0400 Message-ID: <553972D5.2070104@zytor.com> Date: Thu, 23 Apr 2015 15:31:49 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 MIME-Version: 1.0 To: Andy Lutomirski CC: Borislav Petkov , Denys Vlasenko , Linus Torvalds , Brian Gerst , Denys Vlasenko , Ingo Molnar , Steven Rostedt , Oleg Nesterov , Frederic Weisbecker , Alexei Starovoitov , Will Drewry , Kees Cook , the arch/x86 maintainers , Linux Kernel Mailing List Subject: Re: [PATCH] x86/asm/entry/32: Restore %ss before SYSRETL if necessary References: <1429792491-5978-1-git-send-email-dvlasenk@redhat.com> <20150423211015.GS28327@pd.tnic> <55396617.4020303@zytor.com> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 767 Lines: 20 On 04/23/2015 03:29 PM, Andy Lutomirski wrote: >> >> Yes, the NULL SS is a special thing in 64-bit mode. I agree that >> context-switching it is probably the way to go; it should be cheap >> enough. We might even be able to conditionalize it on an X86_BUG_ flag. > > I still don't see why context switches are a better place than just > before sysret, but I could be convinced. > Because there are way more sysrets than context switches, and Linux is particularly sensitive to system call latency, by design. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/