[SATLUG] kvm questions

Borries Demeler demeler at biochem.uthscsa.edu
Sun Apr 28 11:40:53 CDT 2013

I came across a couple of oddities and I was wondering if anyone here has
some insights.  A while ago I installed a 64-bit slackware version on my
wife's computer, added the 32-bit compatibility layer for Slackware, and
then added KVM/QEMU to her machine. My old laptop is 32-bit and doesn't
have the necessary CPU flag (grep vmx /proc/cpuinfo) to run virtual
machines, as explained on http://www.linux-kvm.org/page/Processor_support.
It also only has  2GB of RAM, which would stress the system to run the
host plus one or more vm's.

Long story, but I bought a new I7 laptop, installed 64bit
Slackware-current, everything works great...  In the process, I swapped
the 0.5 TB drive from my old 32-bit laptop with the 200 GB drive from my
wife's laptop, and synchronized my wife's laptop with the 64-bit install
I made on the new I7.  I did that because my wife's laptop has a 8 hour
battery which is great for those transatlantic flights I occasionally
need to go on. Now both my wife's and my new I7 laptop look and act
identical and we both can exchange them easily.

Now here is the surprise: I took the old 32 bit laptop and for kicks
rebooted it with the old drive from my wife's 64-bit Slackware install,
and to my great surprise, not only did it boot and run just fine on my
32-bit box (Intel Core2 Duo T5200, 32-bit, 1.6 GHZ), but it also ran
the KVM images I had installed on it without any issue (ok, they ran slow,
but they did run just fine, including a WIndows XP image I had built on
my wife's computer). I didn't have to do a thing! I did not expect this.

Have other people been successful installing KVM on a 32 bit CPU without 
vmx support?

I guess the fact that the 64-bit install runs fine on a 32-bit box can be 
explained by the fact that I installed the 32-bit compatibility layer and 
recompiled all libs in 32-bit mode. Although I am not sure why the kernel
(which is custom compiled) ended up running in 32-bit mode, I *thought* I
had compiled it in 64-bit mode. I must be missing something...

I'd be curious if anyone has any insights here.

Thanks, -Borries

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