linux-kernel - Re: Sysenter crash with Nested Task Bit set

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Date:	Mon, 18 Sep 2006 17:24:58 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andi Kleen <ak@...e.de>
Cc:	Linus Torvalds <torvalds@...l.org>, Andrew Morton <akpm@...l.org>,
	Chuck Ebbert <76306.1226@...puserve.com>,
	In Cognito <defend.the.world@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>, bcrl@...ck.org
Subject: Re: Sysenter crash with Nested Task Bit set


* Andi Kleen <ak@...e.de> wrote:

> >  #define switch_to(prev,next,last) do {					\
> >  	unsigned long esi,edi;						\
> > -	asm volatile("pushl %%ebp\n\t"					\
> > +	asm volatile("pushfl\n\t"		/* Save flags */	\
> > +		     "pushl %%ebp\n\t"					\
> 
> We used to do that pushfl/popfl some time ago, but Ben removed it 
> because it was slow on P4.  Ok, nobody thought of that case back then.

I _should_ have thought of that though, because when this change was 
done originally i had to reintroduce it both for exec-shield and for 
-rt, so apparently it must have triggered in certain circumstances - i 
just didnt notice the reason. (but recent exec-shield and -rt patches 
dont have this revert, so the condition must have gone away. But it was 
a long time ago.)

	Ingo
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