linux-kernel - Re: Regression: boot failure on AMD Elan TS-5500

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Message-ID: <487036D7.4050400@zytor.com>
Date:	Sat, 05 Jul 2008 20:07:03 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Sean Young <sean@...s.org>, Jeremy Fitzhardinge <jeremy@...p.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org
Subject: Re: Regression: boot failure on AMD Elan TS-5500

Eric W. Biederman wrote:
> Sean Young <sean@...s.org> writes:
> 
>> On Mon, Jun 30, 2008 at 02:52:10PM -0700, Jeremy Fitzhardinge wrote:
>>> It's a bit odd that the boot loader neglected to set up ds properly, but 
>>> changing the testb line to
>>>
>>> 	testb $(1<<6), %cs:BP_loadflags(%esi)
>>>
>>> should work.  (Or perhaps a %ss: override would be better?)
>> Yup, it does (%cs: prefix).
> 
> Guys I have a fuzzy memory of reads and definitely writes through %cs not working,
> on some processor models.  i386?
> 

You can never write through %cs in protected mode.

You can read through %cs: in protected mode unless %cs contains an 
execute-only descriptor.

	-hpa
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