From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754530AbaCENII (ORCPT ); Wed, 5 Mar 2014 08:08:08 -0500 Received: from merlin.infradead.org ([205.233.59.134]:51311 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751569AbaCENIF (ORCPT ); Wed, 5 Mar 2014 08:08:05 -0500 Date: Wed, 5 Mar 2014 14:07:49 +0100 From: Peter Zijlstra To: Steven Rostedt Cc: mingo@kernel.org, hpa@zytor.com, paulus@samba.org, linux-kernel@vger.kernel.org, acme@ghostprotocols.net, seiji.aguchi@hds.com, jolsa@redhat.com, vincent.weaver@maine.edu, tglx@linutronix.de, hpa@linux.intel.com, linux-tip-commits@vger.kernel.org Subject: Re: [tip:x86/urgent] x86, trace: Fix CR2 corruption when tracing page faults Message-ID: <20140305130749.GR3104@twins.programming.kicks-ass.net> References: <20140228160526.GD1133@krava.brq.redhat.com> <20140305111415.GU9987@twins.programming.kicks-ass.net> <20140305072022.6f69f699@gandalf.local.home> <20140305122535.GA9987@twins.programming.kicks-ass.net> <20140305073344.2f179931@gandalf.local.home> <20140305125421.GB9987@twins.programming.kicks-ass.net> <20140305130224.GQ3104@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140305130224.GQ3104@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 05, 2014 at 02:02:24PM +0100, Peter Zijlstra wrote: > > It also puts trace_page_fault_entries() and trace_do_page_fault() under > > CONFIG_TRACING. I could only find the entry_32.S user; I suppose the > > 64bit one is hidden by CPP goo somewhere? > > > +trace_errorentry page_fault normal_do_page_fault > > ah found it; its in there. That also means the normal_do_page_fault() > thing won't actually compile proper. > > Lemme do one with that. --- arch/x86/mm/fault.c | 33 +++++++++++++++++++++++---------- 1 file changed, 23 insertions(+), 10 deletions(-) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index e7fa28bf3262..a10c8c792161 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -1020,8 +1020,12 @@ static inline bool smap_violation(int error_code, struct pt_regs *regs) * This routine handles page faults. It determines the address, * and the problem, and then passes it off to one of the appropriate * routines. + * + * This function must have noinline because both callers + * {,trace_}do_page_fault() have notrace on. Having this an actual function + * guarantees there's a function trace entry. */ -static void __kprobes +static void __kprobes noinline __do_page_fault(struct pt_regs *regs, unsigned long error_code, unsigned long address) { @@ -1245,31 +1249,38 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code, up_read(&mm->mmap_sem); } -dotraplinkage void __kprobes +dotraplinkage void __kprobes notrace do_page_fault(struct pt_regs *regs, unsigned long error_code) { + unsigned long address = read_cr2(); /* Get the faulting address */ enum ctx_state prev_state; - /* Get the faulting address: */ - unsigned long address = read_cr2(); + + /* + * We must have this function tagged with __kprobes, notrace and call + * read_cr2() before calling anything else. To avoid calling any kind + * of tracing machinery before we've observed the CR2 value. + * + * exception_{enter,exit}() contain all sorts of tracepoints. + */ prev_state = exception_enter(); __do_page_fault(regs, error_code, address); exception_exit(prev_state); } -static void trace_page_fault_entries(struct pt_regs *regs, +#ifdef CONFIG_TRACING +static void trace_page_fault_entries(unsigned long address, struct pt_regs *regs, unsigned long error_code) { if (user_mode(regs)) - trace_page_fault_user(read_cr2(), regs, error_code); + trace_page_fault_user(address, regs, error_code); else - trace_page_fault_kernel(read_cr2(), regs, error_code); + trace_page_fault_kernel(address, regs, error_code); } -dotraplinkage void __kprobes +dotraplinkage void __kprobes notrace trace_do_page_fault(struct pt_regs *regs, unsigned long error_code) { - enum ctx_state prev_state; /* * The exception_enter and tracepoint processing could * trigger another page faults (user space callchain @@ -1277,9 +1288,11 @@ trace_do_page_fault(struct pt_regs *regs, unsigned long error_code) * the faulting address now. */ unsigned long address = read_cr2(); + enum ctx_state prev_state; prev_state = exception_enter(); - trace_page_fault_entries(regs, error_code); + trace_page_fault_entries(address, regs, error_code); __do_page_fault(regs, error_code, address); exception_exit(prev_state); } +#endif /* CONFIG_TRACING */