Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753831AbaG2RCL (ORCPT ); Tue, 29 Jul 2014 13:02:11 -0400 Received: from mail-lb0-f172.google.com ([209.85.217.172]:43506 "EHLO mail-lb0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751739AbaG2RCJ (ORCPT ); Tue, 29 Jul 2014 13:02:09 -0400 MIME-Version: 1.0 In-Reply-To: <20140729165416.GA967@redhat.com> References: <3f649f5658a163645e3ce15156176c325283762e.1405992946.git.luto@amacapital.net> <20140728173723.GA20993@redhat.com> <20140729165416.GA967@redhat.com> From: Andy Lutomirski Date: Tue, 29 Jul 2014 10:01:47 -0700 Message-ID: Subject: Re: [PATCH v3 6/8] x86: Split syscall_trace_enter into two phases To: Oleg Nesterov Cc: "linux-kernel@vger.kernel.org" , Kees Cook , Will Drewry , X86 ML , "linux-arm-kernel@lists.infradead.org" , Linux MIPS Mailing List , linux-arch , LSM List , Alexei Starovoitov , "H. Peter Anvin" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 29, 2014 at 9:54 AM, Oleg Nesterov wrote: > On 07/28, Andy Lutomirski wrote: >> >> On Mon, Jul 28, 2014 at 10:37 AM, Oleg Nesterov wrote: >> > Hi Andy, >> > >> > I am really sorry for delay. >> > >> > This is on top of the recent change from Kees, right? Could me remind me >> > where can I found the tree this series based on? So that I could actually >> > apply these changes... >> >> https://git.kernel.org/cgit/linux/kernel/git/kees/linux.git/log/?h=seccomp/fastpath >> >> The first four patches are already applied there. > > Thanks! > >> > If I understand correctly, syscall_trace_enter() can avoid _phase2() above. >> > But we should always call user_exit() unconditionally? >> >> Damnit. I read that every function called by user_exit, and none of >> them give any indication of why they're needed for traced syscalls but >> not for untraced syscalls. On a second look, it seems that TIF_NOHZ >> controls it. > > Yes, just to trigger the slow path, I guess. > >> I'll update the code to call user_exit iff TIF_NOHZ is >> set. > > Or perhaps it would be better to not add another user of this (strange) flag > and just call user_exit() unconditionally(). But, yes, you need to use > from "work = flags & (_TIF_WORK_SYSCALL_ENTRY & ~TIF_NOHZ)" then.\ user_exit looks slow enough to me that a branch to try to avoid it may be worthwhile. I bet that explicitly checking the flag is actually both faster and clearer. That's what I did for v4. --Andy > >> > And we should always set X86_EFLAGS_TF if TIF_SINGLESTEP? IIRC, TF can be >> > actually cleared on a 32bit kernel if we step over sysenter insn? >> >> I don't follow. If TIF_SINGLESTEP, then phase1 will return a nonzero >> value, > > Ah yes, thanks, I missed this. > > Oleg. > -- Andy Lutomirski AMA Capital Management, LLC -- 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/