check if VT-x is activated without having to reboot in Linux?

Question

I have a laptop with Intel Core i5 M 450 @ 2.40GHz which apparently has VT-x but not VT-d. I have Ubuntu 12.04 32bit but would like to have a virtual 64bit terminal-based Linux running on it. How do I know if the BIOS has this VT-x feature activated without having to reboot?

Cutting

Answer 1

You can use rdmsr from msr-tools to read register IA32_FEATURE_CONTROL (address 0x3a). The kernel module msr has to be loaded for this.

On most Linux systems:

sudo modprobe msr
sudo rdmsr 0x3a

Values 3 and 5 mean it's activated.

Blitz

sudo rdmsr 0x3a gives me 5 – Cutting

As far as I understand 3 and 5 mean VT-x is activated. – Blitz

Here's a bit more on those MSR bits: thomas-krenn.com/en/wiki/… security.stackexchange.com/questions/15555/… – Poteat

I am getting value "7" with Linux kernel version 4.8.15, so the VMXON/VT-x option is set and is locked? Interesting. – Slavism

On AMD Ryzen I get rdmsr: CPU 0 cannot read MSR 0x0000003a. – Colligate

Installing msr-tools package on Ubuntu 16.04 (Xenial Xerus) is as easy as running the following command on terminal: sudo apt-get update sudo apt-get install msr-tools – Woken

This fails on a AMD RX-427BB too: rdmsr: CPU 0 cannot read MSR 0x0000003a – Ashcroft

Answer 2

You can use

sudo kvm-ok

from cpu-checker. On Intel, which has the most complicated logic, kvm-ok checks that if bit 0 of rdmsr 0x3a (the lock bit) is set, bit 2 (which allows virt use outside of SMX mode, something to do with trusted boot) must also be set. If the output of rdmsr 0x3a is anything but 1 or 3, you will be able to use kvm. kvm will set bit 2 of the msr if necessary, I expect virtualbox and the rest have the same logic.

Poteat

Not available in Fedora repositories FC36 – Metrify

Answer 3

Install cpu-checker and run "kvm-ok"

If the CPU is enabled, you should see something like:

INFO: /dev/kvm exists
KVM acceleration can be used

othewise

INFO: /dev/kvm does not exist
HINT:   sudo modprobe kvm_intel
INFO: Your CPU supports KVM extensions
INFO: KVM (vmx) is disabled by your BIOS
HINT: Enter your BIOS setup and enable Virtualization Technology (VT),
   and then hard poweroff/poweron your system
KVM acceleration can NOT be used

Precede

On RHEL derivatives we have virt-host-validate which is provided by libvirt-client – Michelson

on Ryzen Fedora 36 virt-host-validate says "Checking if device /dev/kvm exists : FAIL (Check that the 'kvm-intel' or 'kvm-amd' modules are loaded & the BIOS has enabled virtualisation). Which doesn't completely clarify whether I need to re-boot to check the BIOS (although kvm-amd is not loaded according to lsmod) – Metrify

@shgnlnc: 2023: available for debian and many other distros now! – Converse

Answer 4

you can use:

sudo apt-get update
sudo apt-get install cpu-checker
kvm-ok

Eyestrain

Answer 5

I found that scai's answer doesn't work on my AMD Ryzen systems.

This however works really well for me, even on Intel:

if systool -m kvm_amd -v &> /dev/null || systool -m kvm_intel -v &> /dev/null ; then
    echo "AMD-V / VT-X is enabled in the BIOS/UEFI."
else
    echo "AMD-V / VT-X is not enabled in the BIOS/UEFI"
fi

(systool is found in the sysfsutils package on most distros.)

For Intel's VT-D / AMD's IOMMU, I came up with this solution:

if compgen -G "/sys/kernel/iommu_groups/*/devices/*" > /dev/null; then
    echo "AMD's IOMMU / Intel's VT-D is enabled in the BIOS/UEFI."
else
    echo "AMD's IOMMU / Intel's VT-D is not enabled in the BIOS/UEFI"
fi

(It even worked for me if the iommu kernel parameters are not set.)

Colligate

Note: This requires the sysfsutils package, but does not return an error if you don't have it (it just returns "you don't have virt stuff"). – Ashcroft

Answer 6

In linux you can check cpuinfo:

cat /proc/cpuinfo| egrep "vmx|svm"

Tomcat

This will only show if VT-x is supported by the CPU, not if it is activated in the BIOS. – Blitz

Are you sure? When I'm inside my vm it give me an empty line but my cpu supports amd-v? In cpu-z I can see amd-v even when I disabled secure virtual machine in the bios? – Tomcat

@Betterdev I'm not sure the virtual CPU is relevant. Anyway, by saying a CPU info tool reports the presence of AMD-V, despite it being unusable because you disabled SVM in the firmware, you're proving scai's point... – Uncaredfor

This only shows if the CPU has one of those particular extensions; it won't show anything relevant to the BIOS configuration. Check out the full output without grep to see what it's about. – Neisa

Answer 7

A simple approach to confirm that Vt-D is enabled in the BIOS is through the Linux system. If the VT-D is enable in the BIOS and Iommu=on in the grub.cfg then the below folder structure is created automatically to hold the Virtual devices.

/sys/kernel/iommu_groups/0/devices/0000:00:00.0

Whereas if either one of the options VT-D or Iommu is not configured/enabled then the above mentioned folder structure is not created. This behavior is confirmed in CentOS 7.4 and Ubuntu. Hopefully this behavior is similar for other operating systems as well but this would need to be confirmed.

Amply

On Ryzen and Fedora 36 I have /sys/kernel/iommu_groups/0/devices/0000:00:01.0/ (01 not 00). And can't run KVM and don't know if I have to reboot to check BIOS. – Metrify

Answer 8

Coming late to this party but it may be a long-lived question/answer. On Ryzen, Fedora 36, none of the other answers completely clarify whether I need to reboot. Red Hat provides this

In short, to check AMD CPU:

$ grep -E 'svm|vmx' /proc/cpuinfo

(but I know that Ryzen is capable) Then,

# lsmod | grep kvm

To check for kvm_amd or kvm_intel. No kvm_amd module loaded, so that suggests a re-boot to check BIOS is needed. Will update later.

Metrify

Yes, it was disabled in BIOS. Hard to find on Gigabyte A320M. Hidden under MIT / Advanced Frequency Settings! – Metrify