Disable KVM Support for QEMU

Message

rralf · Post by **rralf** » Wed Dec 19, 2012 3:11 pm

Hi!

Is it possible to disable KVM support for qemu? My system doesn't support VT, so i don't need and want KVM.

When trying to start my VM, qemu complains:

# qemu-kvm
Could not access KVM kernel module: No such file or directory
failed to initialize KVM: No such file or directory
No accelerator found!

# qemu-system-x86_64 1
Could not access KVM kernel module: No such file or directory
failed to initialize KVM: No such file or directory
No accelerator found!

There's no useflag KVM for qemu, so how may i disable it?

Thanks in advance!

rralf · Post by **rralf** » Wed Dec 19, 2012 5:00 pm

Got the solution:

There's a (undocumented) -no-kvm CMDline switch.

In my opinion, there should be a KVM useflag for qemu, being disabled at default.
kvm should be opt-in.

Etal · Post by **Etal** » Wed Dec 19, 2012 5:34 pm

Not exactly undocumented...

$ qemu-kvm --help | grep no-kvm
-no-kvm disable KVM hardware virtualization
-no-kvm-irqchip disable KVM kernel mode PIC/IOAPIC/LAPIC
-no-kvm-pit disable KVM kernel mode PIT
-no-kvm-pit-reinjection

Post by Hu » Thu Dec 20, 2012 1:16 am

rralf wrote:In my opinion, there should be a KVM useflag for qemu, being disabled at default.
kvm should be opt-in.

I disagree. Most CPUs sold these days have support for VT-x / SVM, so disabling it by default because some users cannot use it is overkill. If there are specific libraries that are only used when KVM is enabled, then a USE flag might be appropriate, but it should still default to enabling KVM unless the system administrator sets otherwise.