linux-kernel - Re: [patch V2 28/29] x86/irq/64: Remap the IRQ stack with guard pages

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Message-ID: <20190408163632.zssld3xhrcekfi77@treble>
Date:   Mon, 8 Apr 2019 11:36:32 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [patch V2 28/29] x86/irq/64: Remap the IRQ stack with guard pages

On Mon, Apr 08, 2019 at 09:18:00AM -0700, Andy Lutomirski wrote:
> On Sun, Apr 7, 2019 at 11:46 PM Thomas Gleixner <tglx@...utronix.de> wrote:
> >
> > On Sun, 7 Apr 2019, Andy Lutomirski wrote:
> > > On Sun, Apr 7, 2019 at 3:44 PM Thomas Gleixner <tglx@...utronix.de> wrote:
> > > > Actually we have: save_stack_trace()
> > > >
> > >
> > > Like I did here:
> > >
> > > https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/log/?h=WIP.x86/stackguards
> >
> > Kinda, but what that code wants is to skip any entry before 'caller'. So we
> > either add something like save_stack_trace_from() which is trivial on x86
> > because unwind_start() already has an argument to hand in the start of
> > stack or we filter out the entries up to 'caller' in that code.
> >
> >
> 
> Whoops!
> 
> I could add a save_stack_trace_from() or I could add a "caller"
> argument to struct stack_trace.  Any preference as to which looks
> better?  The latter seems a little nicer to me.

The current official way to do that is to use the stack_trace "skip"
field.  That's a hack though because it relies on inlining decisions.

It would be nicer if the skip interface were pointer-based like your
suggestion.

-- 
Josh