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Date:      Wed, 22 Aug 2001 01:27:49 -0700
From:      Peter Wemm <peter@wemm.org>
To:        tlambert2@mindspring.com
Cc:        Mitsuru IWASAKI <iwasaki@jp.FreeBSD.org>, arch@FreeBSD.ORG, audit@FreeBSD.ORG, kumabu@t3.rim.or.jp
Subject:   Re: CFR: Timing to enable CR4.PGE bit 
Message-ID:  <20010822082749.ED86038FD@overcee.netplex.com.au>
In-Reply-To: <3B836737.9C15EA8@mindspring.com> 

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Terry Lambert wrote:
> Peter Wemm wrote:
> > Terry Lambert wrote:
> > > Mitsuru IWASAKI wrote:
> > > > > This part is fine.
> > > >
> > > > OK, I'll commit this one first.
> > >
> > > What does setting PGE early do for you?
> > 
> > The change is to avoid violating the rules in the CPU developers
> > guide.  Did you read the thread?
> 
> Yes.  I still don't get what rules are being broken (no one
> quoted anything in comments inline in the code, citing the
> relevent pages in the guide, with a URL for the guide, for
> example).
> 
> Let me ask again: what was broken before that is now fixed?

The very first article in the thread said:

========
According to developer's manual from Intel site,
ftp://download.intel.com/design/PentiumII/manuals/24319202.pdf
----
2.5. CONTROL REGISTERS
[snip]
PGE
(2-17)
Page Global Enable (bit 7 of CR4). (Introduced in the P6 family
processors.) Enables the global page feature when set; disables the
global page feature when clear. [snip] In addition, the bit must not
                                                    ^^^^^^^^^^^^^^^^
be enabled before paging is enabled via CR0.PG. Program correctness
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
may be affected by reversing this sequence, and processor performance
will be impacted.
----

Currently, we enable CR4.PGE bit in create_pagetables, then enable
CR0.PG in locore.s.  This seems to violate Intel's note.
======

This was in:
Message-id: <20010809035801V.iwasaki@jp.FreeBSD.org>
Subject: CFR: Timing to enable CR4.PGE bit
From: Mitsuru IWASAKI <iwasaki@jp.FreeBSD.org>
Date: Thu, 09 Aug 2001 03:58:01 +0900
To: arch@FreeBSD.ORG
Cc: audit@FreeBSD.ORG, kumabu@t3.rim.or.jp

.. which is why I asked if you read the entire thread.  I thought that
quote was quite clear that we were in violation.

Cheers,
-Peter
--
Peter Wemm - peter@FreeBSD.org; peter@yahoo-inc.com; peter@netplex.com.au
"All of this is for nothing if we don't go to the stars" - JMS/B5


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