Re: Running pae kernel on non-pae system

[Dom <toyer@rpdom.net>]

On 23/02/13 18:36, Debian@paulscrap.com wrote:
> Hi Folks,
>
> 	Last night I updated an older laptop of mine from Squeeze to Wheezy.
> It went fine, but I did run into an odd particularity.
>
> 	This system (Dell D505) has a Pentium M processor.  My understanding is
> that the Pentium M's are just about the only modern(ish) processor
> without pae, and thus kernels with pae compiled in can't run on it. (pae
> doesn't show up in the cpu flags)
>
> 	During the upgrade I did get warnings about it not supporting pae, so I
> did make sure to install the 486 image, but forgot to remove the 686-pae
> (removed 686, though).  That's not a big deal, though.  It just means
> I'd have to select the 486 kernel to boot up and fix it, right?
>
> 	I wasn't paying attention during reboot, and it went to 686-pae by
> default.  Imagine my surprise when it started up with no problems.  It's
> still running on that kernel!
>
> 	Any ideas?  Was my understanding about pae wrong? Can the recent Debian
> kernels disable pae on their own (something I didn't think was
> possible)?  Do I have a magical Pentium M?
>
> 	Some info from the system below:
>
> $ uname -a
> Linux MIT-D505-L 3.2.0-4-686-pae #1 SMP Debian 3.2.35-2 i686 GNU/Linux
>
> $ cat /proc/cpuinfo
> processor	: 0
> vendor_id	: GenuineIntel
> cpu family	: 6
> model		: 13
> model name	: Intel(R) Pentium(R) M processor 1.60GHz
> stepping	: 6
> microcode	: 0x18
> cpu MHz		: 600.000
> cache size	: 2048 KB
> fdiv_bug	: no
> hlt_bug		: no
> f00f_bug	: no
> coma_bug	: no
> fpu		: yes
> fpu_exception	: yes
> cpuid level	: 2
> wp		: yes
> flags		: fpu vme de pse tsc msr mce cx8 sep mtrr pge mca cmov clflush
> dts acpi mmx fxsr sse sse2 ss tm pbe up bts est tm2
> bogomips	: 1198.81
> clflush size	: 64
> cache_alignment	: 64
> address sizes	: 36 bits physical, 32 bits virtual
> power management:

I think the pae bit will only be used by CPUs that support it, otherwise 
it will be ignored and run normally. Only some "really old" CPUs (like 
some others I do run) won't be supported.

My laptop shows:

dom@oz:~$ cat /proc/cpuinfo
processor	: 0
vendor_id	: GenuineIntel
cpu family	: 6
model		: 9
model name	: Intel(R) Pentium(R) M processor 1600MHz
stepping	: 5
microcode	: 0x7
cpu MHz		: 600.000
cache size	: 1024 KB
fdiv_bug	: no
hlt_bug		: no
f00f_bug	: no
coma_bug	: no
fpu		: yes
fpu_exception	: yes
cpuid level	: 2
wp		: yes
flags		: fpu vme de pse tsc msr mce cx8 sep mtrr pge mca cmov clflush 
dts acpi mmx fxsr sse sse2 tm pbe up bts est tm2
bogomips	: 1196.90
clflush size	: 64
cache_alignment	: 64
address sizes	: 36 bits physical, 32 bits virtual
power management:

and an even older laptop gives:

dom@rodney:~$ cat /proc/cpuinfo
processor	: 0
vendor_id	: GenuineIntel
cpu family	: 6
model		: 8
model name	: Celeron (Coppermine)
stepping	: 1
microcode	: 0xf
cpu MHz		: 498.435
cache size	: 128 KB
fdiv_bug	: no
hlt_bug		: no
f00f_bug	: no
coma_bug	: no
fpu		: yes
fpu_exception	: yes
cpuid level	: 2
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 sep mtrr pge mca cmov pse36 
mmx fxsr sse up
bogomips	: 996.87
clflush size	: 32
cache_alignment	: 32
address sizes	: 36 bits physical, 32 bits virtual
power management:

Both running the 3.2.0-4-686-pae kernel

--
Dom