New Linux Patches Enhance Intel Nested Virtualization Performance On Linux

[erek]

“As part of the fix is introducing a cache for L1 APIC pages for enhancing the performance of the unmanaged guest memory:

"This eliminates expensive memremap/memunmap cycles for each L2 VM entry/exit, providing substantial performance improvements when using unmanaged memory such as guest_memfd or memory passed with mem= kernel parameter.

The persistent caching approach maintains correctness through proper invalidation detection while avoiding the overhead of repeated mapping operations."

No specific benchmark numbers were provided publicly for quantifying the performance impact of this overhead for nested VM use-cases.

See this patch series for those interested in the work to enhance the nested VMX performance under KVM for Intel CPUs on Linux.”

Source; https://www.phoronix.com/news/Linux-KVM-Nested-Intel-VMX-Perf

 

[Zarathustra[H]]

What is nested virtualization?

Running a VM inside of a VM?

What on earth is the real world use case for that?

 

[erek]

Running a VM inside of a VM?

yeah i believe so

it seems very inefficient

 

[CrimsonKnight13]

What is nested virtualization?

Running a VM inside of a VM?

What on earth is the real world use case for that?

Nested Virtualization, usually used for testing different configurations in lab & dev environments
https://pve.proxmox.com/wiki/Nested_Virtualization

 

[Nobu]

yeah i believe so

it seems very inefficient

Well, with proper driver and hardware support, it shouldn't be too inefficient. Obviously, you probably wouldn't want to do it for most production workloads. But, it might be useful for sandboxing small appliances that are only needed by one virtual machine.