Sequoia VMs can cause kernel panics

If you are beta-testing macOS 15 Sequoia in a lightweight virtual machine on an Apple silicon Mac, beware that it can cause the host to suffer a kernel panic. Although I haven’t tested this with other virtualisers, my understanding is that the danger applies to them all, and not just my own Viable and Vimy.

Sequoia developer beta 2, both versions of developer beta 3, and I expect the first public beta, are already hungry for memory. In Sonoma and earlier VMs, if you give the guest 16 GB of memory, it’s likely to use considerably less than that. Those betas of Sequoia will probably use a little more than is allocated to them. But that will double if you restart the VM, and if your host Mac has insufficient memory for twice that VM’s original allocation, it’s likely to suffer a kernel panic with the VM still open.

Previously, in Sonoma and earlier, restarting the VM results in the VM Service for the virtualiser (as shown in Activity Monitor) yielding almost all its memory when restarting, and that rising during booting of the VM. In Sequoia, memory is fully retained during the restart, and then rises until it reaches twice that allocated to the VM, or your Mac panics if it runs out of physical memory first.

I’m very grateful to Joe for reporting this. He has sent a Feedback report to Apple, and I hope this is fixed in the next beta release. In the meantime, don’t restart any Sequoia VM unless your Mac has more than twice the free memory allocated to the VM.

I’d be grateful if those using other virtualisers could confirm whether those are also affected. I suspect they are, as the virtualiser doesn’t normally handle restarting of the VM, but leaves that to the host and guest macOS.