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How to fix “KVM: Entry Failed, Hardware Error 0x7” in Nested Virtualization

by | Mar 25, 2025

Learn how to fix “KVM: Entry Failed, Hardware Error 0x7” in nested virtualization. Our KVM Support team is here to help you with your questions and concerns.

How to fix “KVM: Entry Failed, Hardware Error 0x7” in Nested Virtualization

According to our Experts, the “KVM: entry failed, hardware error 0x7” message indicates that a virtual machine failed to start due to an invalid control field in the Virtual Machine Control Structure. This issue commonly happens in nested virtualization, where a VM is run inside another VM.

Impact of the Error

  • The virtual machine fails to start.
  • Unexpected pauses in the VM.
  • The VM cannot be resumed and often requires a reset.
  • Nested virtualization does not function properly.

Causes and Fixes

1. Nested Virtualization Not Supported or Enabled

The host machine or the L1 VM may not have nested virtualization enabled in the BIOS or KVM configuration.

Click here for the Solution.
  1. First, run the following command to check if your CPU supports virtualization:
    grep -E 'vmx|svm' /proc/cpuinfoCopy Code

    If we see vmx (Intel) or svm (AMD), virtualization is supported.

  2. Also, enable Virtualization in BIOS:
    1. Restart the machine and enter the BIOS.
    2. Locate “Virtualization Technology,” “VT-x,” “AMD-V,” or “SVM” under the Advanced or CPU Configuration section.
    3. Enable it, save the changes, and exit BIOS.
  3. Then, enable Nested KVM:
    echo "options kvm_intel nested=1" | sudo tee /etc/modprobe.d/kvm-intel.conf
    sudo modprobe -r kvm_intel
    sudo modprobe kvm_intel
    Copy Code

    Remember to replace kvm_intel with kvm_amd for AMD processors.

  4. Furthermore, verify Nested Virtualization:
    cat /sys/module/kvm_intel/parameters/nestedCopy Code

    If the output is Y or 1, nested virtualization is enabled.

2. Incompatible CPU Configuration

The guest VM may enter an invalid state due to unsupported CPU modes.

Click here for the Solution.
  1. First, edit the VM configuration using:
    virsh edit <instance>Copy Code
  2. Then, modify the CPU settings in the XML file:
    
    <cpu mode='host-passthrough' check='none'>
    <feature policy='require' name='vmx'/>
    </cpu>
    Copy Code

    Host-passthrough provides the best performance but may cause issues during VM migration. And, host-model standardizes features for better portability.

  3. Save the file and restart the VM.

3. Virtual Disk Image Damage

Corrupt virtual disk images can prevent the VM from running.

Click here for the Solution.
  1. To begin with, check the disk image:
    qemu-img check /path/to/your/disk.imgCopy Code
  2. Then, repair the disk image if errors are found:
    qemu-img check -r all /path/to/the/disk.imgCopy Code

Remember to always back up the disk image before attempting repairs.

4. Insufficient Permissions or Resource Access

The user running the VM may lack necessary permissions.

Click here for the Solution.
  1. Add the user to the KVM group:
    sudo usermod -a -G kvm $USER
    newgrp kvm
    Copy Code
  2. Verify file permissions:
    ls -l /path/to/your/disk.img
    sudo chmod g-w /path/to/your/disk.img
    Copy Code
  3. Log out and log back in to apply group membership changes.

5. Conflicting Kernel Modules or Drivers

Conflicts between kernel modules can interfere with KVM operation.

Click here for the Solution.
  1. Check loaded KVM modules:
    lsmod | grep kvmCopy Code
  2. Manually load KVM modules if missing:
    sudo modprobe kvm_intel
    sudo modprobe kvm
    Copy Code

    Use kvm_amd for AMD processors.

  3. Identify conflicts by checking system logs for errors:
    cat /var/log/syslog | grep kvmCopy Code

    If necessary, unload conflicting modules and retry.

6. Hardware Issues

Underlying hardware problems can trigger KVM errors.

Click here for the Solution.
  1. Run hardware diagnostics using manufacturer tools or third-party utilities.
  2. Check the CPU temperatures to prevent overheating issues.
  3. Test with different hardware, if possible, to rule out component failure.

Prevention Tips

To avoid encountering this error in the future, consider these best practices:

  • Keep the system updated.
  • Monitor VM logs for early detection of issues:
    tail -f /var/log/libvirt/qemu/vm-name.logCopy Code
  • Back up virtual disk images regularly to prevent data loss.
  • Monitor system resources to ensure the host machine is not overloaded.
  • Use stable configurations instead of frequently changing VM settings.
  • Thoroughly test nested virtualization setups before deployment.

[Need assistance with a different issue? Our team is available 24/7.]

Conclusion

With the above steps, we can effectively troubleshoot and resolve “KVM: entry failed, hardware error 0x7”, ensuring smooth operation of our nested VMs.

In brief, our Support Experts demonstrated how to fix “KVM: Entry Failed, Hardware Error 0x7” in nested virtualization.

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