Set fpu on mshv returns unexpected result

[dblnz]

This failure has been observed on CI.

The tests sets the vCPU FPU registers to known values, then retrieves them and checks for the expected values.
The returned values is different, notice the last_ip field which reads 0xADBEEF_00000000 instead of the 0xDEADBEEF_00000000 that has been set.

CI Output

``` failures:

---- hypervisor::hyperlight_vm::x86_64::tests::reset_vcpu_simple stdout ----

thread 'hypervisor::hyperlight_vm::x86_64::tests::reset_vcpu_simple' panicked at src/hyperlight_host/src/hypervisor/hyperlight_vm/x86_64.rs:1596:9:
assertion left == right failed
left: CommonFpu { fpr: [[171, 171, 171, 171, 171, 171, 171, 171, 171, 171, 0, 0, 0, 0, 0, 0], [171, 171, 171, 171, 171, 171, 171, 171, 171, 171, 0, 0, 0, 0, 0, 0], [171, 171, 171, 171, 171, 171, 171, 171, 171, 171, 0, 0, 0, 0, 0, 0], [171, 171, 171, 171, 171, 171, 171, 171, 171, 171, 0, 0, 0, 0, 0, 0], [171, 171, 171, 171, 171, 171, 171, 171, 171, 171, 0, 0, 0, 0, 0, 0], [171, 171, 171, 171, 171, 171, 171, 171, 171, 171, 0, 0, 0, 0, 0, 0], [171, 171, 171, 171, 171, 171, 171, 171, 171, 171, 0, 0, 0, 0, 0, 0], [171, 171, 171, 171, 171, 171, 171, 171, 171, 171, 0, 0, 0, 0, 0, 0]], fcw: 3967, fsw: 4660, ftwx: 171, last_opcode: 291, last_ip: 48905104677404672, last_dp: 14627333964952502272, xmm: [[205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205]], mxcsr: 16256 }
right: CommonFpu { fpr: [[171, 171, 171, 171, 171, 171, 171, 171, 171, 171, 0, 0, 0, 0, 0, 0], [171, 171, 171, 171, 171, 171, 171, 171, 171, 171, 0, 0, 0, 0, 0, 0], [171, 171, 171, 171, 171, 171, 171, 171, 171, 171, 0, 0, 0, 0, 0, 0], [171, 171, 171, 171, 171, 171, 171, 171, 171, 171, 0, 0, 0, 0, 0, 0], [171, 171, 171, 171, 171, 171, 171, 171, 171, 171, 0, 0, 0, 0, 0, 0], [171, 171, 171, 171, 171, 171, 171, 171, 171, 171, 0, 0, 0, 0, 0, 0], [171, 171, 171, 171, 171, 171, 171, 171, 171, 171, 0, 0, 0, 0, 0, 0], [171, 171, 171, 171, 171, 171, 171, 171, 171, 171, 0, 0, 0, 0, 0, 0]], fcw: 3967, fsw: 4660, ftwx: 171, last_opcode: 291, last_ip: 16045690981097406464, last_dp: 14627333964952502272, xmm: [[205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205], [205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205, 205]], mxcsr: 16256 }
stack backtrace:
0: 0x58820d32b432 - std::backtrace_rs::backtrace::libunwind::trace::h9c1aa7b29a521839
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/../../backtrace/src/backtrace/libunwind.rs:117:9
1: 0x58820d32b432 - std::backtrace_rs::backtrace::trace_unsynchronized::hb123c31478ec901c
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/../../backtrace/src/backtrace/mod.rs:66:14
2: 0x58820d32b432 - std::sys::backtrace::_print_fmt::hdda75a118fd2034a
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/sys/backtrace.rs:66:9
3: 0x58820d32b432 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::hf435e8e9347709a8
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/sys/backtrace.rs:39:26
4: 0x58820d3524b3 - core::fmt::rt::Argument::fmt::h9802ea71fd88c728
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/core/src/fmt/rt.rs:173:76
5: 0x58820d3524b3 - core::fmt::write::h0a51fad3804c5e7c
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/core/src/fmt/mod.rs:1465:25
6: 0x58820d328083 - std::io::default_write_fmt::h33ff8981097f58ea
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/io/mod.rs:639:11
7: 0x58820d328083 - std::io::Write::write_fmt::he54474135bb64f2f
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/io/mod.rs:1954:13
8: 0x58820d32b282 - std::sys::backtrace::BacktraceLock::print::h1ec5ce5bb8ee285e
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/sys/backtrace.rs:42:9
9: 0x58820d32caac - std::panicking::default_hook::{{closure}}::h5ffefe997a3c75e4
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/panicking.rs:300:27
10: 0x58820d32c902 - std::panicking::default_hook::h820c77ba0601d6bb
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/panicking.rs:324:9
11: 0x58820d0a0d14 - <alloc::boxed::Box<F,A> as core::ops::function::Fn>::call::hd2d9a835f4b8f423
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/alloc/src/boxed.rs:1980:9
12: 0x58820d0a0d14 - test::test_main_with_exit_callback::{{closure}}::h32c4bc4a085dff05
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/test/src/lib.rs:145:21
13: 0x58820d32d50b - <alloc::boxed::Box<F,A> as core::ops::function::Fn>::call::h8be59125c8e59551
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/alloc/src/boxed.rs:1980:9
14: 0x58820d32d50b - std::panicking::rust_panic_with_hook::h8b29cbe181d50030
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/panicking.rs:841:13
15: 0x58820d32d1fa - std::panicking::begin_panic_handler::{{closure}}::h9f5b6f6dc6fde83e
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/panicking.rs:706:13
16: 0x58820d32b939 - std::sys::backtrace::__rust_end_short_backtrace::hd7b0c344383b0b61
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/sys/backtrace.rs:168:18
17: 0x58820d32ce8d - __rustc[5224e6b81cd82a8f]::rust_begin_unwind
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/panicking.rs:697:5
18: 0x58820ce317a0 - core::panicking::panic_fmt::hc49fc28484033487
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/core/src/panicking.rs:75:14
19: 0x58820ce31af3 - core::panicking::assert_failed_inner::hdec560441e5facaf
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/core/src/panicking.rs:432:17
20: 0x58820ce96d68 - core::panicking::assert_failed::h1ba64c0842938293
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/core/src/panicking.rs:387:5
21: 0x58820d003fae - hyperlight_host::hypervisor::hyperlight_vm::x86_64::tests::reset_vcpu_simple::h00787419276c0c64
at /mnt/vss/_work/hyperlight/hyperlight/src/hyperlight_host/src/hypervisor/hyperlight_vm/x86_64.rs:1596:9
22: 0x58820d0032d7 - hyperlight_host::hypervisor::hyperlight_vm::x86_64::tests::reset_vcpu_simple::{{closure}}::hcfb91abb3387eeb2
at /mnt/vss/_work/hyperlight/hyperlight/src/hyperlight_host/src/hypervisor/hyperlight_vm/x86_64.rs:1561:27
23: 0x58820ce6ea06 - core::ops::function::FnOnce::call_once::h20464213998e4893
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/core/src/ops/function.rs:250:5
24: 0x58820d0a641b - core::ops::function::FnOnce::call_once::h92226b62eea5e740
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/core/src/ops/function.rs:250:5
25: 0x58820d0a641b - test::__rust_begin_short_backtrace::h5403e9ff57c40dab
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/test/src/lib.rs:648:18
26: 0x58820d0a569e - test::run_test_in_process::{{closure}}::hde5ebd764eed8d41
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/test/src/lib.rs:671:74
27: 0x58820d0a569e - <core::panic::unwind_safe::AssertUnwindSafe as core::ops::function::FnOnce<()>>::call_once::h87a841e037538b15
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/core/src/panic/unwind_safe.rs:272:9
28: 0x58820d0a569e - std::panicking::catch_unwind::do_call::hfce8274c0464d7ee
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/panicking.rs:589:40
29: 0x58820d0a569e - std::panicking::catch_unwind::hf1024a3b71e7559a
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/panicking.rs:552:19
30: 0x58820d0a569e - std::panic::catch_unwind::h32f944874226e619
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/panic.rs:359:14
31: 0x58820d0a569e - test::run_test_in_process::he51794d4da2ed405
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/test/src/lib.rs:671:27
32: 0x58820d0a569e - test::run_test::{{closure}}::hc41d5e32018fb032
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/test/src/lib.rs:592:43
33: 0x58820d06a474 - test::run_test::{{closure}}::hb8e8bc84d9b1bbba
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/test/src/lib.rs:622:41
34: 0x58820d06a474 - std::sys::backtrace::rust_begin_short_backtrace::h725872d9e0edd537
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/sys/backtrace.rs:152:18
35: 0x58820d06dbfa - std::thread::Builder::spawn_unchecked::{{closure}}::{{closure}}::hc300ae8ae2205644
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/thread/mod.rs:559:17
36: 0x58820d06dbfa - <core::panic::unwind_safe::AssertUnwindSafe as core::ops::function::FnOnce<()>>::call_once::h98ba43e212713b1f
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/core/src/panic/unwind_safe.rs:272:9
37: 0x58820d06dbfa - std::panicking::catch_unwind::do_call::h3367b31a744e4f14
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/panicking.rs:589:40
38: 0x58820d06dbfa - std::panicking::catch_unwind::h0a7a52dbc375b4fd
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/panicking.rs:552:19
39: 0x58820d06dbfa - std::panic::catch_unwind::he34cdfe5914307ff
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/panic.rs:359:14
40: 0x58820d06dbfa - std::thread::Builder::spawn_unchecked::{{closure}}::h73faeaeb9205adc3
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/thread/mod.rs:557:30
41: 0x58820d06dbfa - core::ops::function::FnOnce::call_once{{vtable.shim}}::h7c65d33fb6595d81
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/core/src/ops/function.rs:250:5
42: 0x58820d3307ff - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce>::call_once::h8703e59bc8145d18
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/alloc/src/boxed.rs:1966:9
43: 0x58820d3307ff - std::sys::pal::unix::thread::Thread::new::thread_start::h1ff51d6e85162efd
at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/sys/pal/unix/thread.rs:107:17
44: 0x70ed7ce8bca7 -
45: 0x70ed7cf0fabc -
46: 0x0 -

failures:
hypervisor::hyperlight_vm::x86_64::tests::reset_vcpu_simple

</details>

[dblnz]

After a rerun, the test passed. This is a spurious error which we might encounter in the future.