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

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Message-ID: <4829C9EE.7020306@zytor.com>
Date:	Tue, 13 May 2008 10:03:42 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Cyrill Gorcunov <gorcunov@...il.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

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.

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
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