From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754992Ab2F1MI6 (ORCPT ); Thu, 28 Jun 2012 08:08:58 -0400 Received: from mail-wi0-f170.google.com ([209.85.212.170]:50267 "EHLO mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752941Ab2F1MIz (ORCPT ); Thu, 28 Jun 2012 08:08:55 -0400 Date: Thu, 28 Jun 2012 14:08:49 +0200 From: Frederic Weisbecker To: Jiri Olsa Cc: acme@redhat.com, a.p.zijlstra@chello.nl, mingo@elte.hu, paulus@samba.org, cjashfor@linux.vnet.ibm.com, eranian@google.com, gorcunov@openvz.org, tzanussi@gmail.com, mhiramat@redhat.com, robert.richter@amd.com, fche@redhat.com, linux-kernel@vger.kernel.org, masami.hiramatsu.pt@hitachi.com, drepper@gmail.com, asharma@fb.com, benjamin.redelings@nescent.org, Borislav Petkov , "H. Peter Anvin" , Roland McGrath Subject: Re: [RFC 09/23] x86_64: Store userspace rsp in system_call fastpath Message-ID: <20120628120846.GA28527@somewhere> References: <1340120894-9465-1-git-send-email-jolsa@redhat.com> <1340120894-9465-10-git-send-email-jolsa@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1340120894-9465-10-git-send-email-jolsa@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 19, 2012 at 05:48:00PM +0200, Jiri Olsa wrote: > hi, > I'd need help with this change.. basically it works, but I guess > I could alter the FIXUP_TOP_OF_STACK macro as well, so the rsp is > not initialized twice in slowpath. > > But it seems quite complex.. so not really sure at the moment ;) > > ideas? > > thanks, > jirka > > --- > Storing the userspace rsp into the pt_regs struct for the > system_call fastpath (syscall instruction handler). > > Following part of the pt_regs is allocated on stack: > (via KERNEL_STACK_OFFSET) > > unsigned long ip; > unsigned long cs; > unsigned long flags; > unsigned long sp; > unsigned long ss; > > but only ip is actually saved for fastpath. > > For perf post unwind we need at least ip and sp to be able to > start the unwind, so storing the old_rsp value to the sp. > > Signed-off-by: Jiri Olsa > Cc: Borislav Petkov > Cc: H. Peter Anvin > Cc: Roland McGrath > --- > arch/x86/kernel/entry_64.S | 5 +++++ > 1 files changed, 5 insertions(+), 0 deletions(-) > > diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S > index 111f6bb..0444917 100644 > --- a/arch/x86/kernel/entry_64.S > +++ b/arch/x86/kernel/entry_64.S > @@ -516,6 +516,11 @@ GLOBAL(system_call_after_swapgs) > SAVE_ARGS 8,0 > movq %rax,ORIG_RAX-ARGOFFSET(%rsp) > movq %rcx,RIP-ARGOFFSET(%rsp) > +#ifdef CONFIG_PERF_EVENTS > + /* We need rsp in fast path for perf post unwind. */ > + movq PER_CPU_VAR(old_rsp), %rcx > + movq %rcx,RSP-ARGOFFSET(%rsp) > +#endif Another solution is to set/unset some TIF flag in perf_event_sched_in/out such that we take the syscall slow path (tracesys) which records every non-scratch registers. I can see that old_rsp is not saved in pt_regs by SAVE_REST so this may be something to add in tracesys. This way we don't bloat the syscall fastpath with a feature only used by some developers. > CFI_REL_OFFSET rip,RIP-ARGOFFSET > testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET) > jnz tracesys > -- > 1.7.7.6 >