fix(quickemu): improve TSC flag detection for macOS on AMD CPUs

[flexiondotorg]

Summary

macOS Monterey and newer can freeze on AMD Ryzen 4000U/5000U mobile CPUs when run as guests under QEMU/KVM. The root cause is a mismatch in how the host reports TSC capabilities and what macOS/QEMU expect.

Technical explanation

• AMD reports the TSC feature as constant_tsc while macOS/QEMU expect invtsc. Functionally these indicate the same behaviour (an invariant, non-stopped TSC), but quickemu did not recognise constant_tsc as equivalent to invtsc for AMD hosts.

What this fix does

1. Improve check_cpu_flag to recognise constant_tsc as equivalent to invtsc on AMD hosts.
2. Add explicit TSC flags for macOS guests on AMD hosts: +tsc,+tsc-deadline,+invtsc.

Important caveat

This is the best mitigation we can apply at the quickemu wrapper level. If macOS still freezes after this change the limitation is likely in QEMU/KVM's TSC virtualisation on these specific mobile CPU architectures and will need fixes upstream.

Fallback options if this fix doesn't resolve the issue

• Use macOS Big Sur (11.x) which has more lenient TSC requirements.
• Use AMD Ryzen 6000U series or desktop Ryzen CPUs; these are known to work.
• Use an Intel host; Intel hosts do not exhibit this issue.

Related issue

Closes #1273

[cubic-dev-ai]

1 issue found across 1 file

Confidence score: 4/5

• Safe to merge overall; the only noted issue is a moderate-severity duplication of the +invtsc flag handling.
• Duplicate +invtsc addition in quickemu could lead to redundant CPU flag configuration (already handled via configure_cpu_flag for AMD).
• Pay close attention to quickemu - duplicate +invtsc flag handling.

Prompt for AI agents (all issues)

Check if these issues are valid — if so, understand the root cause of each and fix them.


<file name="quickemu">

<violation number="1" location="quickemu:477">
P2: Duplicate `+invtsc` flag: The `invtsc` flag is already processed by the loop above (line 468) via `configure_cpu_flag`, which will add `+invtsc` for AMD CPUs thanks to the `check_cpu_flag` fix. Adding it again here causes duplication. Remove `+invtsc` from this line since only `+tsc` and `+tsc-deadline` are the additional flags needed.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}