On Sat, 4 Apr 2009, Matthias Kaehlcke wrote:
> hi robert,
>
> El Sat, Apr 04, 2009 at 08:02:29AM -0400 Robert P. J. Day ha dit:
>
> > is there an easy way to tell if a running kernel has KVM
> > functionality? from "make menuconfig", we can see the KVM tristate
> > selections under "Virtualization:"
> >
> > --- Virtualization
> > <M> Kernel-based Virtual Machine (KVM) support
> > < > KVM for Intel processors support (NEW)
> > < > KVM for AMD processors support (NEW)
> >
> > so if i have no access to the corresponding config file, how can i
> > tell if a kernel has any or all of the above?
> >
> > first, i know that if you choose to build all of the above as
> > modules, you'll get kvm.ko, kvm-intel.ko and kvm-amd.ko, so i can
> > check the modules. but if any of that has been built into the kernel,
> > is there a way to tell? something under /proc, perhaps?
>
> kvm_init() registers the device class 'kvm':
> http://lxr.linux.no/linux+v2.6.29/virt/kvm/kvm_main.c#L2289
>
> i guess it is called at system initialization when kvm support has
> been built into the kernel. if that is the case you could check for
> the existence of /sys/class/kvm
ah, quite right, i should have checked there. and let me ask a
couple more questions, which i would normally answer for myself by
testing but, at the moment, i have no system running a kernel with
built-in kvm support. (as an aside, is anyone out there running a
recent kernel with built-in kvm that can verify the above?)
if you look at the menuconfig snippet above, you can see that, in
addition to selecting *generic* kvm support, this still won't do you
any good unless you further select one of the two available
(x86-based) kvm hardware extensions (Intel vmx or AMD svm). so, the
obvious questions:
* i'm assuming that it's *legal* to select generic kvm support
without selecting additional CPU-specific support, which will only
mean that, if matthias is correct, you'll see /sys/class/kvm even when
you have no actual kvm support.
* depending on which of the two (or possibly both) CPU-specific virt
support you choose, how could you verify that *those* were currently
supported in your running kernel?
if they were built modular, i can already see that you'd have the
modules kvm-intel.ko or kvm-amd.ko. but if they're built in, how
could you tell? would they show up as subdirs under /sys/class/kvm?
again, anyone who can verify this on an actual system, feel free.
thanks.
rday
--
p.s. depending on which CPU support you choose, you'd end up
compiling one or both of arch/x86/kvm/{svm,vmx}.c. i guess i could
just peruse those source files and see if they register something
under /sys.
========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry:
Have classroom, will lecture.
http://crashcourse.ca Waterloo, Ontario, CANADA
========================================================================
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