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

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Message-ID: <454CE7D9.3070308@vmware.com>
Date:	Sat, 04 Nov 2006 11:19:53 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Chuck Ebbert <76306.1226@...puserve.com>
Cc:	Andi Kleen <ak@...e.de>, 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

Chuck Ebbert wrote:
> In-Reply-To: <454B850C.3050402@...are.com>
>
> On Fri, 03 Nov 2006 10:06:04 -0800, Zachary Amsden wrote:
>
>   
>> Chuck Ebbert wrote:
>>     
>>> IOPL is implicitly saved and restored on task switch,
>>> so explicit check is no longer needed.
>>>       
>> Nack.  This is used for paravirt-ops kernels that use IOPL'd userspace.  
>>     
>
> How does that work?  In the stock kernel, anything done by
> the call to set_iopl_mask() (that was removed by the patch)
> will be nullified by the 'popfl' at the end of the switch_to()
> macro.
>   

Who put a popfl back in switch_to?  I took it out some time ago.  It 
should not be there.  The only reason for it was to stop IOPL leaking 
from one process to another from a sleep during a sysenter based system 
call.

Zach
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