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

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Date:   Mon, 8 Apr 2019 18:44:49 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...nel.org>
cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        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, 8 Apr 2019, 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 whole interface with struct stack_trace sucks. Why is skip and max
entries in that struct and not an argument? I went through all the call
sites and it just makes me shudder. That terminate trace with ULONG_MAX is
another horrible hack which is then undone on several callsites
again. Before we add more hacky stuff to it, lets cleanup that whole mess
first.

Thanks,

	tglx