linux-kernel - Re: [PATCH] x86: enable PAT for amd k8 and fam10h

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Message-ID: <47E85593.4030104@zytor.com>
Date:	Mon, 24 Mar 2008 18:29:55 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	yhlu.kernel@...il.com
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: enable PAT for amd k8 and fam10h

Yinghai Lu wrote:
> [PATCH] x86: enable PAT for amd k8 and fam10h
> 
> make known_pat_cpu to think amd k8 and fam10h is ok too.
> 
> also make tom2 below to be WRBACK
> 
> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> index f74505f..a9e1a27 100644
> --- a/arch/x86/mm/pat.c
> +++ b/arch/x86/mm/pat.c
> @@ -49,6 +49,12 @@ static int pat_known_cpu(void)
>  			return 1;
>  		}
>  	}
> +	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD &&
> +	     boot_cpu_data.x86 >= 0xf && boot_cpu_data.x86 <= 0x11) {
> +		if (cpu_has_pat) {
> +			return 1;
> +		}
> +	}
>  
>  	pat_wc_enabled = 0;
>  	printk(KERN_INFO "CPU and/or kernel does not support PAT.\n");

This really should be handled through a CPU flag.  Specifically, it 
should be handled by disabling the PAT flag if PAT is unusable or 
suspect of being unusable; it should *NOT* be stashed away in a 
completely separate piece of code.

	-hpa
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