1.8: CVM register validation (#3960)

[jennagoddard]

Add per-register / per-MSR validation on the SetVpRegisters and WRMSR paths to help prevent invalid VMSA state which cause failures at VMRUN

cherry-pick: #3960

[Copilot]

Pull request overview

Adds centralized validation for CVM guest register and MSR writes to reduce the chance of constructing architecturally-invalid guest state that can fail at VMRUN/entry.

Changes:

• Move canonical-address checking into x86defs for reuse across the codebase.
• Add shared CVM MSR validation (validate_cvm_msr_write) and SetVpRegisters per-register validation/normalization in hardware_cvm.
• Wire MSR validation into both TDX and SNP MSR-write paths; add SNP-specific FS/GS base canonical checks; add unit tests for the new validation logic.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
vmm_core/virt_support_x86emu/src/translate.rs	Switches to the shared x86defs::is_canonical_address helper and updates tests accordingly.
vm/x86/x86defs/src/lib.rs	Adds new x86defs constants and exports is_canonical_address for reuse.
openhcl/virt_mshv_vtl/src/processor/tdx/mod.rs	Adds CVM MSR-write validation before applying TDX MSR updates.
openhcl/virt_mshv_vtl/src/processor/snp/mod.rs	Adds CVM MSR-write validation and enforces canonical FS/GS base values in the guest’s current paging mode.
openhcl/virt_mshv_vtl/src/processor/hardware_cvm/mod.rs	Introduces shared validation helpers for MSRs and SetVpRegisters (including CR0 normalization), plus unit tests.

[github-actions]

3 Petri tests failed (1 unstable)