linux-kernel - Re: [PATCH v9 2/3] trace,x86: add x86 irq vector tracepoints

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Date:	Fri, 15 Feb 2013 20:59:53 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Seiji Aguchi <seiji.aguchi@....com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Thomas Gleixner (tglx@...utronix.de)" <tglx@...utronix.de>,
	"'mingo@...e.hu' (mingo@...e.hu)" <mingo@...e.hu>,
	"Borislav Petkov (bp@...en8.de)" <bp@...en8.de>,
	Satoru Moriya <satoru.moriya@....com>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	"Luck, Tony (tony.luck@...el.com)" <tony.luck@...el.com>
Subject: Re: [PATCH v9 2/3] trace,x86: add x86 irq vector tracepoints

On Fri, 2013-02-15 at 16:09 -0800, H. Peter Anvin wrote:
> On 02/04/2013 02:49 PM, Seiji Aguchi wrote:
> > +
> > +static void switch_to_trace_idt(void *arg)
> > +{
> > +	store_idt(this_cpu_ptr(&orig_idt_descr));
> > +	load_idt(&trace_idt_descr);
> > +
> > +	return;
> > +}
> > +
> > +static void restore_original_idt(void *arg)
> > +{
> > +	if (this_cpu_read(orig_idt_descr.address)) {
> > +		load_idt(this_cpu_ptr(&orig_idt_descr));
> > +		this_cpu_write(orig_idt_descr.address, 0);
> > +	}
> > +
> > +	return;
> > +}
> > +
> 
> The base address of the IDT doesn't generally change... the one
> exception is when we do the funny NMI workaround.
> 
> For that reason, I would be happier if we just restored the standard
> value instead of saving/restoring stuff.
> 
> The above code is probably broken if either side is in the funny NMI
> zone... unless you can guarantee it is *always* in the funny NMI zone
> (in which case you can just load nmi_idt_descr instead.
> 
> Steve R., do you know what the constraints are with respect to that?
> 

This switch should always be outside the funny NMI and debug zone.
I think you missed a patch that I sent you to deal with exactly this:

https://lkml.org/lkml/2013/2/1/532

I sent it directly to you, maybe it got buried in your INBOX.

-- Steve


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