linux-kernel - Re: [PATCH v2 00/18] Entry stack switching

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Date:   Wed, 22 Nov 2017 07:36:36 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     X86 ML <x86@...nel.org>, Borislav Petkov <bpetkov@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v2 00/18] Entry stack switching


* Ingo Molnar <mingo@...nel.org> wrote:

> 
> * Andy Lutomirski <luto@...nel.org> wrote:
> 
> > This sets up stack switching, including for SYSCALL.  I think it's
> > in decent shape.
> > 
> > Known issues:
> >  - I think we're going to want a way to turn the stack switching on and
> >    off either at boot time or at runtime.  It should be fairly straightforward
> >    to make it work.
> > 
> >  - I think the ORC unwinder isn't so good at dealing with stack overflows.
> >    It bails too early (I think), resulting in lots of ? entries.  This
> >    isn't a regression with this series -- it's just something that could
> >    be improved.
> > 
> > Ingo, patch 1 may be tip/urgent material.  It fixes what I think is
> > a bug in Xen.  I'm having a hard time testing because it's being
> > masked by a bigger unrelated bug that's keeping Xen from booting
> > when configured to hit the bug I'm fixing.  (The latter bug goes at
> > least back to v4.13, I think I know roughtly what's wrong, and I've
> > reported it to the maintainers.)
> 
> Hm, with this series the previous IRQ vector bug appears again:
> 
> [   51.156370] do_IRQ: 16.34 No irq handler for vector
> [   57.511030] do_IRQ: 16.34 No irq handler for vector
> [   57.528335] do_IRQ: 16.34 No irq handler for vector
> [   57.533256] do_IRQ: 16.34 No irq handler for vector
> [   63.991913] do_IRQ: 16.34 No irq handler for vector
> [   63.996810] do_IRQ: 16.34 No irq handler for vector
> 
> I've attached the reproducer config. Note that the system appears to be working to 
> a certain extent (I could ssh to it and extract its config), but produces these 
> warnings sporadically.
> 
> Also note that this is the same AMD system tha had irq-tracing/lockdep troubles 
> yesterday. So maybe this warning is related and we either have broken lockdep, or 
> these IRQ vector warnings.

Yeah, so I just double checked, if from the latest series I revert:

  x86/entry/64: Fix entry_SYSCALL_64_after_hwframe() IRQ tracing

then I (no surprise) get the bootup lockdep warning - but don't get the IRQ vector 
warnings.

Thanks,

	Ingo