MacBooks running older versions of macOS
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Owners of Apple's newest Macs with M4 chips can't run older versions of macOS in a virtual machine due to a mysterious boot issue.
Running a virtual machine with older generations of macOS can have its uses, ranging from security and development to simply being able to run software that won’t work with newer versions of macOS. However, there seems to be a problem when it comes to using a virtual machine in this way on an M4 chip.
As detailed by Eclectic Light Co. and pointed out by Csaba Fitzl, issues have been found when attempting to run versions of macOS released prior to macOS 13.4 Ventura in a virtual machine on an M4 Mac. There is no issue on an M1, M2, or M3 Mac, as this only happens on the M4.
Starting a virtual machine with an older macOS installation results in a black screen and a boot failure. This has been found to occur regardless of the settings used for the virtual machine itself, and even in Recovery Mode.
The actual source of the issue is unknown due to the inability to access the logs to see what actually happened. There is also no host log crash and everything seemed to be working fine until the VM crashed.
The only real clue that was found is that despite multiple virtual cores being allocated, there is actually only one active on the host. This suggests that the crash occurs at some point in the boot process before the VM kernel loads the other cores, which is the early kernel boot phase.
The most likely guess at this point is that there is a bug somewhere in the early kernel boot process. This would require fixing the bug in the affected macOS kernels and making new IPSW image files available.
While this was reported to Apple in Feedback FB15774587 and stated that it affects UTM, it is unlikely that Apple will do anything about this issue. The report says Apple probably won't bother, as it hasn't released revised IPSW versions in this way before.
For those who need to keep older versions of macOS running as a virtual machine, the immediate answer is to stick with Mac models with M3 or earlier versions and think seriously about future Mac upgrades.
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