linux-kernel - Re: [PATCH 2/5] x86: PAT: fix ambiguous paranoia check in pat

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Date:	Wed, 11 Jun 2008 00:55:23 +0200
From:	Rene Herman <rene.herman@...access.nl>
To:	Andreas Herrmann <andreas.herrmann3@....com>
CC:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Suresh B Siddha <suresh.b.siddha@...el.com>
Subject: Re: [PATCH 2/5] x86: PAT: fix ambiguous paranoia check in pat_init()

On 10-06-08 16:05, Andreas Herrmann wrote:

> Starting with commit 8d4a4300854f3971502e81dacd930704cb88f606 (x86:
> cleanup PAT cpu validation) the PAT CPU feature flag is not cleared
> anymore. Now the error message
> 
>   "PAT enabled, but CPU feature cleared"
> 
> in pat_init() is misleading.

No, it's correct. This is to be read as "The PAT feature is enabled in 
the kernel but the CPU claims to not have PAT". The message is not a 
leftover from the old flag-clearing setup or anything; it was introduced 
in the patch that disabled that.

> Furthermore the current code does not check for existence of the PAT
> CPU feature flag if a CPU is whitelisted in validate_pat_support.

Which is okay-ish, or at least by design it seems. The paranoia check in 
pat.c will catch this case.

The current setup is okay really. The only thing it still wants is a 
commandline whitelist switch but that needs a somewhat different setup 
as validate_pat_support() is too early for __setup() or early_param().

Rene.
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