Apple Silicon and Virtual Machines: Beating the 2 VM Limit (2023)

5 hours ago

Apple Silicon hosts are limited to running only two macOS guest virtual machines at a time due to restrictions in the SLA.
The VM limit check is enforced in the kernel (XNU), not in userspace, specifically within the hv_vm_* functions.
A boot-arg, hv_apple_isa_vm_quota, can override the VM limit, but it requires booting a development kernel or modifying the release kernel.
To use the override, one must create and boot a development kernel collection, which involves steps like downloading a Kernel Debug Kit and configuring the system in recoveryOS.
After configuration, virtualization solutions like UTM or VMware can run more than two macOS VMs, with testing showing up to nine VMs active.
This feature has been available since macOS Monterey, but it's undocumented and intended for internal use.
Using a custom kernel collection disables streamlined OS updates, requiring a reversion to the stock kernel for updates to proceed.
Potential future improvements include automating the kernel collection process and developing a kext to override the VM quota without a custom kernel.

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