linux-kernel - Re: [patch 1/2] x86: head_64.S cleanup - use straight move to CR4 register

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Message-ID: <20080513170717.GE6921@cvg>
Date:	Tue, 13 May 2008 21:07:17 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	tglx@...utronix.de, mingo@...hat.com, linux-kernel@...r.kernel.org,
	jirislaby@...il.com
Subject: Re: [patch 1/2] x86: head_64.S cleanup - use straight move to CR4
	register

[H. Peter Anvin - Tue, May 13, 2008 at 10:03:42AM -0700]
> Cyrill Gorcunov wrote:
>> There is no need for testing the values because we already know
>> what they should be. Just set them in straight way.
>
> He isn't testing them, he's setting individual bits.

not exactly - bts: bit test and set

>
> Either of these is pretty silly; the right way to do this is:
>
> 	movl	$(X86_CR4_PAE|X86_CR4_PGE), %eax
> 	movq	%rax, %cr4
>
> A movl in 64-bit mode zero extends.
>
> 	-hpa
>
ok, thanks Peter, i'll update in minute ;)

		- Cyrill -
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