Let the native-host backend boot on a host CPU profile

[Enrique Saurez (esaurez)]

Stacked on #421. Lets the opt-in native-host backend boot on a host CPU profile.

Summary

• OpenVMM boots every microVM on a CPU profile, by default the built-in profile of the host's CPU generation (see CPU profiles). A host that no built-in profile serves, or whose hypervisor does not support its profile, therefore cannot start native sandboxes, while nvx.py run --cpu-profile host opts such development hosts in to a profile that OpenVMM derives from the host.
• NvxHostConfig::with_host_cpu_profile(true) does the same for the native backend. It sets the native library's additive host-CPU-profile launch flag (16), which adds --cpu-profile host to the RAM-overlay launch. A library that predates the flag rejects it rather than ignoring it.
• The example takes --cpu-profile auto|host, and NVXHOST_TEST_CPU_PROFILE=host runs the guest tests on a host profile. The README says when to use it, and that OpenVMM derives a host profile from the hypervisor at every cold boot and does not pin it.

Dependencies

• Requires the matching private host library with the host-CPU-profile launch flag.

Validation

• Each PR head in this stack passes cargo test --all-features and Clippy with -D warnings on all targets with --all-features, on Windows with Rust 1.93 (135, 137, 139, 139, and 140 unit tests).

• At the top of the stack (5b0a315), on Windows and on Linux with Rust 1.93: the crate's CI checks, which are fmt, Clippy with --all-features and with --no-default-features, tests with --all-features and with default features, docs with -D warnings, cargo +1.89 check, and, on Linux, the macOS build check. The pinned library test passes against freshly built nvxhost.dll and libnvxhost.so.

• Guest suite at the top of the stack, 20 tests, --release --test-threads=1, each checking that no OpenVMM process outlives its sandbox, with dev's Linux 6.18.38 kernel:

  • Windows/WHP on an AMD EPYC 7763, which amd.milan.v1 serves: all pass, in about 100 s, and again with a host profile;
  • Linux/MSHV on an AMD EPYC 9V74, which no built-in profile serves: all pass with a host profile, in about 82 s.

• OpenVMM's --cpu-fingerprint reports E_PROFILE_HOST_UNKNOWN on the AMD EPYC 9V74 MSHV host, so every cold boot with the default profile fails there; with NVXHOST_TEST_CPU_PROFILE=host, all 20 guest tests pass. On the WHP host, all 20 pass both ways.

• New unit tests cover the launch flags and the example's --cpu-profile parser, and the pinned library test checks that the flag adds --cpu-profile host.

Notes

• cpu_profile: pin AMD Genoa and Turin CPU profiles nanvix/openvmm#119 proposes a built-in Genoa profile, but OpenVMM rejects it on that host's MSHV (E_PROFILE_UNSUPPORTED): the profile derives from a KVM fingerprint, and that hypervisor presents a different surface, such as its CPUID leaf range, the 0x80000021 bits, and the AVX-512 and CET XSAVE components. A host profile remains the way to run there.

[Enrique Saurez (esaurez)]

Folded into #418, which now carries the whole change. The native library implements this feature behind the model types that #418 adds, and its guest tests are part of the end-to-end suite there.