linux-kernel - Re: This kernel requires the following features not present on the CPU... (on a VIA C7 CPU)

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Message-ID: <464CB726.6090201@simon.arlott.org.uk>
Date:	Thu, 17 May 2007 21:12:22 +0100
From:	Simon Arlott <simon@...e.lp0.eu>
To:	Claas Langbehn <claas@...tdir.de>
CC:	LKML <linux-kernel@...r.kernel.org>, hpa@...or.com,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: This kernel requires the following features not present on the
 CPU... (on a VIA C7 CPU)

On 17/05/07 13:27, Claas Langbehn wrote:
> I have got a VIA EPIA EX15000G Mini-ITX mainboard with a C7 VIA Esther 
> processor (1500MHz).
I have Jetway's J7F4K with the same CPU.

> C7 CMPXCHG8 - enable/disable (Disable to install windows NT 4.0) and
> C7 No Execute (NX) - enable/disable
Without those options in the BIOS setup.

>  > This kernel requires the following features not present on the CPU:
>  > 0:8
> I attached a cpuinfo.txt. When the two flags are disabled, cx8 and nx 
> are not listed there.
I don't have cx8, but I do have nx (which is unused because I have PAE 
disabled...).


On 17/05/07 19:33, H. Peter Anvin wrote:
>> Claas Langbehn wrote:
>> Would it be possible to override the BIOS settings of cx8 and nx and
>> > activate it with linux anyway?
>> > The CPU supports it and I don't see any reason to disable it.
>> > 
>  
> Yes, that code is already in the git.newsetup tree.

Is it automatic? I have CONFIG_X86_CMPXCHG=y without cx8 showing in 
cpuinfo, and it appears to work fine.

Will your changes needlessly prevent the kernel running? Would I be 
right in thinking that the kernel is successfully using cmpxchg even 
though it's considered disabled? I realise people compile kernels 
for the wrong CPU but preventing them working when it's been chosen 
correctly seems wrong.

processor       : 0
vendor_id       : CentaurHauls
cpu family      : 6
model           : 10
model name      : VIA Esther processor 1500MHz
stepping        : 9
cpu MHz         : 800.000 (cpufreq)
cache size      : 128 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu vme de pse tsc msr pae mce apic sep mtrr pge cmov pat clflush acpi mmx fxsr sse sse2 tm nx pni est tm2 rng rng_en ace ace_en ace2 ace2_en phe phe_en pmm pmm_en
bogomips        : 1601.18
clflush size    : 64

-- 
Simon Arlott

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