linux-kernel - Re: [PATCH 04/23] x86, realmode: Move reboot

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Message-ID: <4FAA7C06.1060209@redhat.com>
Date:	Wed, 09 May 2012 16:15:34 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>
CC:	Jarkko Sakkinen <jarkko.sakkinen@...el.com>,
	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
	Michal Marek <mmarek@...e.cz>, Sam Ravnborg <sam@...nborg.org>,
	Joseph Cihula <joseph.cihula@...el.com>,
	Shane Wang <shane.wang@...el.com>
Subject: Re: [PATCH 04/23] x86, realmode: Move reboot_32.S to unified realmode
 code

Il 09/05/2012 15:53, H. Peter Anvin ha scritto:
>> > It's true that it doesn't matter much but still it is a
>> > regression. And it doesn't cause any kind of overhead
>> > or bloat to fix this.
>> > 
> However, the big thing is that we jump to the BIOS with caches off.  I
> personally think it is the wrong thing to do (we don't jump to the real
> reset vector anyway) but it is what has been tested for a long time.

I'm not sure I understand.  The code has

	andl	$0x60000000, %edx	; clear ET/PE
	jz	2f
	...
2:
	andb	$0x10, %dl		; clear CD/WT, %edx is always 0


What I've suggested is:

	testl	$0x60000000, %edx
	jz	2f
	...
2:
	andb	$0x10, %dl		; clear PE only


What would jump to the BIOS with caches on is:

	testl	$0x60000000, %edx
	jz	2f
	...
2:
	andl	$0x10, %edx		; Clear CD/WT/PE


Am I missing something?

Paolo
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