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.
An Overview:
Causes and FixesImpact 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.
- First, run the following command to check if your CPU supports virtualization:
grep -E 'vmx|svm' /proc/cpuinfoIf we see vmx (Intel) or svm (AMD), virtualization is supported.
- Also, enable Virtualization in BIOS:
- Restart the machine and enter the BIOS.
- Locate “Virtualization Technology,” “VT-x,” “AMD-V,” or “SVM” under the Advanced or CPU Configuration section.
- Enable it, save the changes, and exit BIOS.
- 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
Remember to replace kvm_intel with kvm_amd for AMD processors.
- Furthermore, verify Nested Virtualization:
cat /sys/module/kvm_intel/parameters/nestedIf 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.
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- First, edit the VM configuration using:
virsh edit <instance> - Then, modify the CPU settings in the XML file:
<cpu mode='host-passthrough' check='none'>
<feature policy='require' name='vmx'/>
</cpu>
Host-passthrough provides the best performance but may cause issues during VM migration. And, host-model standardizes features for better portability.
- Save the file and restart the VM.
3. Virtual Disk Image Damage
Corrupt virtual disk images can prevent the VM from running.
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- To begin with, check the disk image:
qemu-img check /path/to/your/disk.img - Then, repair the disk image if errors are found:
qemu-img check -r all /path/to/the/disk.img
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.
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- Add the user to the KVM group:
sudo usermod -a -G kvm $USER
newgrp kvm
- Verify file permissions:
ls -l /path/to/your/disk.img
sudo chmod g-w /path/to/your/disk.img
- 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.
- Check loaded KVM modules:
lsmod | grep kvm - Manually load KVM modules if missing:
sudo modprobe kvm_intel
sudo modprobe kvm
Use kvm_amd for AMD processors.
- Identify conflicts by checking system logs for errors:
cat /var/log/syslog | grep kvmIf necessary, unload conflicting modules and retry.
6. Hardware Issues
Underlying hardware problems can trigger KVM errors.
Click here for the Solution.
- Run hardware diagnostics using manufacturer tools or third-party utilities.
- Check the CPU temperatures to prevent overheating issues.
- 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.log - 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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