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Message-ID: <512301F7.4020709@zytor.com>
Date:	Mon, 18 Feb 2013 20:39:19 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Steven Rostedt <rostedt@...dmis.org>
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 02/18/2013 08:24 PM, Steven Rostedt wrote:
> On Mon, 2013-02-18 at 15:49 -0800, H. Peter Anvin wrote:
> 
>> What about the following:
>>
>>> 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.
> 
> Basically what you are saying, is to have his code do what the NMI code
> originally did, but can't now, due to there being another IDT table
> (from Seiji's changes).
> 
> static void switch_to_trace_idt(void *arg)
> {
>      load_idt(&trace_idt_descr);
> }
> 
> static void restore_original_idt(void *arg)
> {
>      load_idt(this_cpu_ptr(&idt_descr));
> }
> 

Yes.  If there needs to be handshaking about whose IDT is currently
installed I'm much happier if that handshake is done explicitly, rather
than as a save/restore function which will break when we have to add
another one which for whatever reason isn't nesting.

	-hpa


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