LoadVM assert on ARM_FEATURE_M for Cortex M3

Host environment

• Operating system: Ubuntu 20.04
• OS/kernel version: Linux 5.15.0-86-lowlatency
• Architecture: x86_64
• QEMU flavor: qemu-system-arm
• QEMU version: v8.0.0 through v8.2.0
• QEMU command line:

  ./qemu-system-arm -cpu cortex-m3 -M mps2-an385 -nographic -drive if=none,format=qcow2,file=test.qcow2 -monitor unix:/tmp/qemu-mon.sock,server,no-wait -serial mon:stdio

Emulated/Virtualized environment

• Operating system: -
• OS/kernel version: -
• Architecture: ARM Cortex M3

Description of problem

This appears to be a similar issue to #1775 (closed) and #1658 (closed)

When running loadvm qemu aborts with this error:

"qemu/target/arm/helper.c:12383: arm_security_space_below_el3: Assertion `!arm_feature(env, ARM_FEATURE_M)' failed."

I've traced the error to pmu_counter_enabled in qemu\target\arm\helper.c:1172
uint64_t mdcr_el2 = arm_mdcr_el2_eff(env) (link is to 8.2.0 release tag)

The issue is caused by attempting to get the MDCR_EL2 register prior to checking if the CPU has ARM_FEATURE_PMU support.

A simple fix seems to be to check for ARM_PMU_ENABLED and returning early if it is not enabled.

Steps to reproduce

1. Start emulation and connect monitor
2. savevm
3. Loadvm

Additional information

See screenshot for stack trace