linux-kernel - Re: [RFC][PATCH 01/14 v2] function_graph: Convert ret

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Date:   Mon, 3 Jun 2019 20:30:49 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Andy Lutomirski <luto@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Namhyung Kim <namhyung@...nel.org>,
        "Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [RFC][PATCH 01/14 v2] function_graph: Convert ret_stack to a
 series of longs

On Fri, 24 May 2019 08:05:53 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> > 
> > > +#define SHADOW_STACK_SIZE (PAGE_SIZE)  
> > 
> > Do we really need that big a shadow stack?
> 
> Well, this is a sticky point. I allow up to 16 users at a time
> (although I can't imagine more than 5, but you never know), and each
> user adds a long and up to 4 more words (which is probably unlikely
> anyway). And then we can have deep call stacks (we are getting deeper
> each release it seems).
> 
> I figured, I start with a page size, and then in the future we can make
> it dynamic, or shrink it if it proves to be too much.

I'd prefer dynamic allocation, based on the number of users or actual
stack starvation.


Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>