Re: [RFC PATCH 00/12] Add RISC-V Worlds ISA support to OpenSBI

On Fri, Jun 26, 2026 at 3:16 AM Yu-Chien Peter Lin <[email protected]> wrote:

Oza: I have started reviewing this series, and will provide comments
in coming days.
>
> This RFC patch series adds support for RISC-V Worlds ISA extensions,
> enabling hardware-enforced isolation boundaries based on World IDs (WIDs)
> by extending the OpenSBI domain framework.
>
> Trust Model and Boot-time Roles
> --------------------------------
>
> The implementation follows the two-phase M-mode trust model:
>
> - RoT M-mode phase: Prior boot stage (ROM/SPL) that may program mwid/
>   mlwidlist and lock mwid before handing off to OpenSBI.
>
> - Regular M-mode phase (OpenSBI): Treats pmwid/pmwidlist/pmlwidlist as
>   read-only input policy from hardware/RoT. Locks mwid during feature
>   detection to prevent later M-mode code from changing its own WID.
>   Programs per-domain mlwid/mwiddeleg based on DT configuration.
>
> Device Tree Bindings
> ---------------------
>
> New CPU properties (per-hart):
> - riscv,pmwid: Platform-defined M-mode World ID
> - riscv,pmwidlist: M-mode permitted WID bitmap (u64, 2 cells)
> - riscv,pmlwidlist: S/U-mode permitted WID bitmap (u64, 2 cells)
>
> New domain properties (per-domain):
> - next-wid: Override S-mode WID for this domain (u32, 1 cell)
> - next-widlist: WID delegation bitmap for this domain (u64, 2 cells)
>
> If a domain lacks next-wid, OpenSBI falls back to pmwid (M-mode and
> S-mode run in the same World).
>
> Example DT snippet:
>
>     cpus {
>         riscv,nworlds = <4>;
>         cpu@0 {
>             riscv,pmwid = <3>;
>             riscv,pmwidlist = <0x0 0xf>;
>             riscv,pmlwidlist = <0x0 0xf>;
>         };
>     };
>
>     chosen {
>         opensbi-domains {
>             trusted-domain {
>                 next-wid = <1>;
>                 next-widlist = <0x0 0x2>;
>             };
>             untrusted-domain {
>                 next-wid = <0>;
>                 next-widlist = <0x0 0x1>;
>             };
>         };
>     };
>
> Known Limitations and Future Work
> ----------------------------------
>
> This RFC implements core functionality but has several areas requiring
> refinement in the future revisions:
>
> 1. WID Validation:
>    - Domain next-wid is NOT validated against pmlwidlist
>    - Domain next-widlist is NOT validated as subset of pmlwidlist
>    - Invalid WID configuration fails at runtime with software-check
>      exceptions rather than at domain registration time
>    - Planned: Add validation in sanitize_domain() to catch errors early
>
> 2. Resume Path mwid Restoration:
>    - Current implementation only re-locks mwid on resume, assuming RoT
>      has already restored the correct WID value
>    - No mechanism to verify or actively restore mwid to RoT-defined value
>
> Specification References
> -------------------------
>
> - RISC-V Worlds ISA Spec: https://github.com/riscv/riscv-worlds
>   (Release: riscv-isa-release-4c81a3f-2026-04-14)
> - Device Tree Proposal: https://lore.kernel.org/all/[email protected]/
>
> Yu-Chien Peter Lin (12):
>   lib: sbi_hart: detect RISC-V Worlds ISA extensions
>   lib: utils: fdt_helper: parse RISC-V Worlds DT properties
>   lib: sbi_hart: enforce riscv,pmwid for Worlds ISA
>   lib: sbi_hart: lock mwid CSR for RoT immutability
>   include: sbi_domain: add Worlds WID fields
>   include: sbi_types: add PRIx64 format macro
>   lib: sbi_domain: print World ID config at boot
>   lib: sbi_init: print M-mode World ID at boot
>   platform: generic: parse root domain WID config from DT
>   lib: utils: fdt_domain: parse per-domain WID properties
>   lib: sbi_domain: add Worlds CSR config on domain entry
>   docs: add RISC-V Worlds next-wid/next-widlist DT properties
>
>  docs/domain_support.md             | 13 ++++++
>  docs/opensbi_config.md             | 13 ++++++
>  include/sbi/riscv_encoding.h       | 12 +++++
>  include/sbi/sbi_domain.h           |  9 ++++
>  include/sbi/sbi_hart.h             | 25 +++++++++++
>  include/sbi/sbi_types.h            |  2 +
>  include/sbi_utils/fdt/fdt_helper.h |  2 +
>  lib/sbi/sbi_domain.c               | 50 +++++++++++++++++++++
>  lib/sbi/sbi_domain_context.c       |  3 ++
>  lib/sbi/sbi_hart.c                 | 71 ++++++++++++++++++++++++++++++
>  lib/sbi/sbi_hsm.c                  |  4 ++
>  lib/sbi/sbi_init.c                 | 13 ++++++
>  lib/utils/fdt/fdt_domain.c         | 15 +++++++
>  lib/utils/fdt/fdt_helper.c         | 61 +++++++++++++++++++++++++
>  platform/generic/platform.c        | 33 +++++++++++++-
>  15 files changed, 324 insertions(+), 2 deletions(-)
>
> --
> 2.43.7
>
>
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