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

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
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   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.

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>
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   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.

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.

1. Add the user to the KVM group:

   sudo usermod -a -G kvm $USER
   newgrp kvm
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2. Verify file permissions:

   ls -l /path/to/your/disk.img
   sudo chmod g-w /path/to/your/disk.img
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3. Log out and log back in to apply group membership changes.

1. Check loaded KVM modules:

   lsmod | grep kvmCopy Code
2. Manually load KVM modules if missing:

   sudo modprobe kvm_intel
   sudo modprobe kvm
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   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.

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.