[GSoC 2026] PCID Support for COCONUT-SVSM

=== Support X86 Process Context Identifiers (PCID) in COCONUT-SVSM ===

COCONUT-SVSM is a Secure Virtual machine Service Module that runs at a
privileged level within a Confidential Virtual Machine (CVM) to provide trusted
services, such as a virtual TPM, to the guest operating system, independent of
the host hypervisor.

The goal of the project is to enhance the COCONUT-SVSM kernel to make use of
the PCID feature on X86 to reduce the number of runtime TLB misses. The work
consists of several steps:

1. Implement generic CPUID feature enumeration support by building a code
   generator which automatically creates a Rust crate from the data provided by
   the X86-CPUID project. Use that generated crate in COCONUT-SVSM for
   detecting the PCID feature and clean up all the open coded CPUID checks.
2. Design and implement a PCID assignment strategy for tasks and threads in the
   COCONUT kernel.
3. Apply the PCIDs in the COCONUT page-tables and adapt the TLB flushing code
   to take PCIDs into account.

'''Links:'''
* AMD64 APM 2 (PCIDs, Section 5.5.1.): https://docs.amd.com/v/u/en-US/24593_3.43 
* X86 cpuid project: https://x86-cpuid.org/
* COCONUT-SVSM: https://github.com/coconut-svsm/svsm/

'''Details:'''
* Skill level: Intermediate
* Languages: Rust