Calling "hv_vm_config_set_el2_enabled(config, true)" but vCPU still starts in EL1

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sergiolpascual OP

Created Feb ’25

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I'm testing the newly introduced nested virt API from Hypervisor.framework on an M3 Pro running 15.3.1.

First, I'm calling "hv_vm_config_get_el2_supported" to confirm the system supports nested virt, then "hv_vm_config_set_el2_enabled" to enable EL2 in the configuration and finally "hv_vm_config_get_el2_enabled" to confirm it's enabled.

After creating the VM with this configuration, I've confirmed with assembly code (checking CurrentEL) that the vCPU is still starting in EL1. Something has definitely changed in the vCPU management, because SMCCC calls that worked fine without calling "hv_vm_config_set_el2_enabled" now trigger an "EC_INSNABORT", but from the guest perspective the vCPU is definitely still in EL1.

Is there an additional requirement in addition to calling to "hv_vm_config_set_el2_enabled" to make the vCPU start in EL2?

Answered by Engineer in 827606022

The Hypervisor framework generally doesn't provide a reset state for the vCPUs. It's best that you program each system register with a default value for the features you are enabling/emulating.

For the current EL state, that is defined by HV_REG_CPSR (the PSTATE). The format of CPSR is the same as SPSR_ELx. To enter at EL2, you'll want to set the M field.

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Answer 1

Engineer OP

Apple

Mar ’25

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The Hypervisor framework generally doesn't provide a reset state for the vCPUs. It's best that you program each system register with a default value for the features you are enabling/emulating.

For the current EL state, that is defined by HV_REG_CPSR (the PSTATE). The format of CPSR is the same as SPSR_ELx. To enter at EL2, you'll want to set the M field.

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Answer 2

sergiolpascual OP

Mar ’25

Yes, that was it, thanks! Coming from KVM, I wrongly assumed HVF would set the vCPU registers on reset to a coherent state. After setting PSTATE (and a couple more registers) to reasonable values for EL2, got Linux booting in hyp mode.

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