linux-kernel - Re: [PATCH 3/4] x86/ftrace: make ftrace_int3

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Message-ID: <20190430142047.GF2589@hirez.programming.kicks-ass.net>
Date:   Tue, 30 Apr 2019 16:20:47 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Nicolai Stange <nstange@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Juergen Gross <jgross@...e.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Andy Lutomirski <luto@...nel.org>,
        Joerg Roedel <jroedel@...e.de>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        live-patching@...r.kernel.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH 3/4] x86/ftrace: make ftrace_int3_handler() not to skip
 fops invocation

On Tue, Apr 30, 2019 at 09:44:45AM -0400, Steven Rostedt wrote:
> On Tue, 30 Apr 2019 12:46:48 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Mon, Apr 29, 2019 at 02:52:50PM -0400, Steven Rostedt wrote:
> > > On Mon, 29 Apr 2019 11:06:58 -0700
> > > Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> > >   
> > > > +void replace_call(void *addr, const void *opcode, size_t len, void *target)
> > > > +{
> > > > +	bp_int3_call_target = target;
> > > > +	bp_int3_call_return = addr + len;
> > > > +	bp_int3_handler_irqoff = emulate_call_irqoff;
> > > > +	text_poke_bp(addr, opcode, len, emulate_call_irqon);
> > > > +}  
> > > 
> > > Note, the function tracer does not use text poke. It does it in batch
> > > mode. It can update over 40,000 calls in one go:  
> > 
> > Note that Daniel is adding batch stuff to text_poke(), because
> > jump_label/static_key stuffs also end up wanting to change more than one
> > site at a time and IPI spraying the machine for every single instance is
> > hurting.
> > 
> > So ideally ftrace would start to use the 'normal' code when that
> > happens.
> 
> Sure, but that's a completely different issue. We would need to solve
> the 'emulate' call for batch mode first.

I don't see a problem there; when INT3 happens; you bsearch() the batch
array to find the one you hit, you frob that into the percpu variables
and do the thing. Or am I loosing the plot again?