[fedora-virt] how can i see if the running kernel has kvm support?

Eduardo Habkost ehabkost at redhat.com
Wed Apr 8 20:24:07 UTC 2009

On Wed, Apr 08, 2009 at 04:05:41PM -0400, Robert P. J. Day wrote:
>   i'm curious as to how to examine a running kernel to see what it has
> in the way of kvm support.
>   i can see that "make menuconfig" gives me the options:
>     KVM                   (KVM)
>       KVM for Intel       (KVM_INTEL)
>       KVM for AMD         (KVM_AMD)
> first question:  technically, i can select generic KVM support without
> selecting either INTEL or AMD support.  can i assume that that's a
> pointless thing to do?  the help text for CONFIG_KVM does seem to
> suggest that you really need to additionally select a processor module
> to make any sense; i was just wondering if there's some obscure
> scenario where having only that generic KVM support had any value.

Yes, it is meaningless to select only KVM without any processor support.
You will just waste memory.

>   next, regardless of whether kvm support is built-in or whether it's
> modular and the modules have been loaded, is there some indication --
> say under /proc or /sys -- that shows the current state of kvm support
> in the kernel?
>   if i had the config file for the running kernel, i could of course
> look at that, but let's assume that i have no such thing, and that kvm
> support is built-in so i can't even check for, say, /sys/module/kvm.
> is there a userspace way to probe and determine kvm support?

You can try looking at /sys/class/misc/kvm.

Inside qemu, you can run the "info kvm" monitor command to make sure kvm
support is really working on your qemu instance.

> rday
> p.s.  just to be clear, kvm support in the kernel doesn't count if
> that kernel is running on a system without HW virt support, for which
> kvm support obviously has no value since it can't be used.  in a case
> like that, i'd like to get the answer that there is *no* support.

The kvm modules fail to load if there is no hardware support, so if you
have /sys/class/misc/kvm, you should have hardware virt support working.


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