linux-kernel - Re: [PATCH 2/9] x86 idle: remove NOP cpuinfo_x86.hlt_works

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Message-ID: <20110331061247.GA24786@elte.hu>
Date:	Thu, 31 Mar 2011 08:12:47 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Len Brown <lenb@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	linux-pm@...ts.linux-foundation.org,
	Len Brown <len.brown@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 2/9] x86 idle: remove NOP cpuinfo_x86.hlt_works_ok flag


* Len Brown <lenb@...nel.org> wrote:

> From: Len Brown <len.brown@...el.com>
> 
> hlt_works_ok was X86_32 only, initialized to 1, and never cleared.
> 
> On 32-bit kernels, this deletes a line from /proc/cpuinfo: "hlt_bug : no"

I think you missed the valid usecase where an old CPU with broken halt is 
booted with the no-hlt boot parameter and does not want to crash in the HLT 
instruction.

That "no-hlt" boot parameter does:

  arch/x86/kernel/cpu/bugs.c:     boot_cpu_data.hlt_works_ok = 0;

We can restrict compatibility, but *please* lets do it *explicitly*, not under 
some 'remove unused code' pretense ...

Could you please list all CPU models that are affected?

Thanks,

	Ingo
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