linux-kernel - Re: [patch] i386: remove IOPL check on task switch

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Message-Id: <200611042102.13026.ak@suse.de>
Date:	Sat, 4 Nov 2006 21:02:12 +0100
From:	Andi Kleen <ak@...e.de>
To:	Zachary Amsden <zach@...are.com>
Cc:	Chuck Ebbert <76306.1226@...puserve.com>,
	Andrew Morton <akpm@...l.org>,
	Linus Torvalds <torvalds@...l.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [patch] i386: remove IOPL check on task switch

 
> Ok, checking shows Linus put it back to stop NT leakage. 

It is also needed to stop AC leakage

> This is  
> correct, but unlikely.  Would be nice to avoid it unless absolutely 
> necessary.  Perhaps xor eflags old and new and only set_system_eflags() 
> if non-ALU bits have changed.

If it's worth it...

If it's worth for the context switch i think it would make 
more sense to do it for the normal restore_flags() etc. which are much
more common (and could be actually handled in most cases with test + jump + sti)

-Andi
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