Reset more vcpu state on snapshot::restore

[ludfjig]

MSRs will be added in another PR.

• Add debug register abstraction over hv implementation
• Removed padding fields from fpu register to simplify comparisons. Not sure why I added them to begin with, we don't need C repr on these. It could possibly allow more efficient into() implementation for kvm/mshv due to single memcyp, but that seems like premature optimization to me
• Reset vcpu state on snapshot::restore
• Added bunch of tests

[jsturtevant]

this should be valid for more than just init paging feature?

[ludfjig]

yes will fix before publishing pr

[jsturtevant]

isn't this duplicating alot of the configuration code we do during VM setup in the test? how will we maintain this with the actual setup? What if there is a difference?

[ludfjig]

This is calling HyperlightVm::new so they should be the same

[Copilot]

Pull request overview

This PR enhances vCPU state management during snapshot restoration by adding debug register abstraction and ensuring all vCPU state is properly reset. The changes follow the established Common* struct pattern for hypervisor abstraction and include comprehensive test coverage across KVM, MSHV, and WHP hypervisors.

Key changes:

• Added CommonDebugRegs abstraction with implementations for all supported hypervisors (KVM, MSHV, WHP)
• Removed padding fields from CommonFpu to simplify comparisons while maintaining correct conversions to hypervisor-specific types
• Implemented reset_vcpu() to reset general purpose registers, debug registers, FPU/XSAVE state, and special registers
• Added reset_vcpu() call in MultiUseSandbox::restore() to ensure clean state after snapshot restoration
• Added extensive tests covering all reset scenarios with both direct state setting and actual code execution

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/hyperlight_host/src/hypervisor/regs/debug_regs.rs	New file implementing CommonDebugRegs abstraction with conversions for KVM, MSHV, and WHP
src/hyperlight_host/src/hypervisor/regs/fpu.rs	Removed pad1 and pad2 fields from CommonFpu; updated all conversions to use literal 0 for padding
src/hyperlight_host/src/hypervisor/regs.rs	Added debug_regs module export
src/hyperlight_host/src/hypervisor/mod.rs	Added debug_regs, set_debug_regs, reset_xsave, and set_xsave methods to Hypervisor trait
src/hyperlight_host/src/hypervisor/kvm.rs	Implemented debug register and xsave methods for KVM hypervisor
src/hyperlight_host/src/hypervisor/hyperv_linux.rs	Implemented debug register and xsave methods for MSHV hypervisor
src/hyperlight_host/src/hypervisor/hyperv_windows.rs	Implemented debug register and xsave methods for WHP; refactored gdb breakpoint code to use new abstractions
src/hyperlight_host/src/hypervisor/hyperlight_vm.rs	Added reset_vcpu() method and comprehensive test suite covering all vCPU state reset scenarios
src/hyperlight_host/src/sandbox/initialized_multi_use.rs	Added reset_vcpu() call in restore() and test to verify debug registers are reset
src/hyperlight_host/src/sandbox/hypervisor.rs	Added Copy and Clone derives to HypervisorType enum
src/hyperlight_host/src/mem/layout.rs	Changed visibility from pub(super) to pub(crate) for methods used by tests
src/tests/rust_guests/simpleguest/src/main.rs	Added SetDr0 and GetDr0 guest functions for testing debug register reset
.github/workflows/ValidatePullRequest.yml	Changed fail-fast from true to false for build-test job to allow all matrix combinations to complete