[RFC PATCH 01/12] lib: sbi_hart: detect RISC-V Worlds ISA extensions

[Pawandeep Oza]

On Fri, Jun 26, 2026 at 3:16 AM Yu-Chien Peter Lin <peter.lin at sifive.com> wrote:
>
> Add detection for RISC-V Worlds ISA extensions (Smwid, Smlwid,
> Smlwidlist, Smwiddeleg, Sswid) via ISA string detection and
> CSR probes.
>
> These feature flags enable subsequent patches to conditionally
> configure World ID CSRs and print boot-time Worlds status.
>
> Signed-off-by: Yu-Chien Peter Lin <peter.lin at sifive.com>
> ---
>  include/sbi/riscv_encoding.h | 12 +++++++++
>  include/sbi/sbi_hart.h       | 10 +++++++
>  lib/sbi/sbi_hart.c           | 51 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 73 insertions(+)
>
> diff --git a/include/sbi/riscv_encoding.h b/include/sbi/riscv_encoding.h
> index ffe7666c..271820fd 100644
> --- a/include/sbi/riscv_encoding.h
> +++ b/include/sbi/riscv_encoding.h
> @@ -400,6 +400,9 @@
>  /* Supervisor Resource Management Configuration CSRs */
>  #define CSR_SRMCFG                     0x181
>
> +/* Supervisor World-ID CSR (Sswid) */
> +#define CSR_SLWID                      0x190
Oza: Misleading comment -
should be
Supervisor WID value for lower privilege modes Register
> +
>  /* Machine-Level Control transfer records CSRs */
>  #define CSR_MCTRCTL                     0x34e
>
> @@ -520,6 +523,15 @@
>  #define CSR_MTINST                     0x34a
>  #define CSR_MTVAL2                     0x34b
>
> +/* Machine World-ID CSRs (Smwid, Smlwid, Smlwidlist, Smwiddeleg) */
> +#define CSR_MLWID                      0x390
> +#define CSR_MWID                       0x391
> +#define CSR_MWIDDELEG                  0x748
> +#define CSR_MLWIDLIST                  0x749
> +
> +/* mwid lock bit */
> +#define MWID_LOCK                      (_UL(1) << (__riscv_xlen - 1))
> +
>  /* Machine Memory Protection */
>  #define CSR_PMPCFG0                    0x3a0
>  #define CSR_PMPCFG1                    0x3a1
> diff --git a/include/sbi/sbi_hart.h b/include/sbi/sbi_hart.h
> index 543393bb..2941809e 100644
> --- a/include/sbi/sbi_hart.h
> +++ b/include/sbi/sbi_hart.h
> @@ -95,6 +95,16 @@ enum sbi_hart_extensions {
>         SBI_HART_EXT_F,
>         /** Hart has D extension */
>         SBI_HART_EXT_D,
> +       /** Hart has Smwid extension */
> +       SBI_HART_EXT_SMWID,
> +       /** Hart has Smlwid extension */
> +       SBI_HART_EXT_SMLWID,
> +       /** Hart has Smlwidlist extension */
> +       SBI_HART_EXT_SMLWIDLIST,
> +       /** Hart has Smwiddeleg extension */
> +       SBI_HART_EXT_SMWIDDELEG,
> +       /** Hart has Sswid extension */
> +       SBI_HART_EXT_SSWID,
>
>         /** Maximum index of Hart extension */
>         SBI_HART_EXT_MAX,
> diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c
> index 21713816..0c584bfc 100644
> --- a/lib/sbi/sbi_hart.c
> +++ b/lib/sbi/sbi_hart.c
> @@ -402,6 +402,11 @@ const struct sbi_hart_ext_data sbi_hart_ext[] = {
>         __SBI_HART_EXT_DATA(v, SBI_HART_EXT_V),
>         __SBI_HART_EXT_DATA(f, SBI_HART_EXT_F),
>         __SBI_HART_EXT_DATA(d, SBI_HART_EXT_D),
> +       __SBI_HART_EXT_DATA(smwid, SBI_HART_EXT_SMWID),
> +       __SBI_HART_EXT_DATA(smlwid, SBI_HART_EXT_SMLWID),
> +       __SBI_HART_EXT_DATA(smlwidlist, SBI_HART_EXT_SMLWIDLIST),
> +       __SBI_HART_EXT_DATA(smwiddeleg, SBI_HART_EXT_SMWIDDELEG),
> +       __SBI_HART_EXT_DATA(sswid, SBI_HART_EXT_SSWID),
>  };
>
>  _Static_assert(SBI_HART_EXT_MAX == array_size(sbi_hart_ext),
> @@ -689,6 +694,52 @@ __pmp_skip:
>         /* Detect if hart support sdtrig (debug triggers) */
>         __check_ext_csr(SBI_HART_PRIV_VER_UNKNOWN,
>                         CSR_TSELECT, SBI_HART_EXT_SDTRIG);
> +       /* Detect if hart supports Smwid (mwid CSR) */
> +       __check_ext_csr(SBI_HART_PRIV_VER_UNKNOWN,
> +                       CSR_MWID, SBI_HART_EXT_SMWID);
> +       /* Detect if hart supports Smlwid (mlwid CSR) */
> +       __check_ext_csr(SBI_HART_PRIV_VER_UNKNOWN,
> +                       CSR_MLWID, SBI_HART_EXT_SMLWID);
> +       /* Detect if hart supports Smlwidlist (mlwidlist CSR). */
> +       __check_ext_csr(SBI_HART_PRIV_VER_UNKNOWN,
> +                       CSR_MLWIDLIST, SBI_HART_EXT_SMLWIDLIST);
> +       /*
> +        * Detect if hart supports Smwiddeleg & Sswid.
> +        * Smwiddeleg requires Smlwid. Sswid requires Smwiddeleg.
> +        */
> +       if (sbi_hart_has_extension(scratch, SBI_HART_EXT_SMLWID)) {
> +               unsigned long old_mwiddeleg, new_mwiddeleg;
> +
> +               old_mwiddeleg = csr_read_allowed(CSR_MWIDDELEG, &trap);
Oza: why not use __check_ext_csr at all the following ?
> +               if (trap.cause)
> +                       goto skip_smwiddeleg;
> +
> +               csr_write_allowed(CSR_MWIDDELEG, &trap, ~0UL);
> +               if (trap.cause)
> +                       goto skip_smwiddeleg;
> +
> +               new_mwiddeleg = csr_read_allowed(CSR_MWIDDELEG, &trap);
> +               if (trap.cause) {
> +                       csr_write(CSR_MWIDDELEG, old_mwiddeleg);
> +                       goto skip_smwiddeleg;
> +               }
> +
> +               if (new_mwiddeleg) {
> +                       __sbi_hart_update_extension(hfeatures,
> +                                                   SBI_HART_EXT_SMWIDDELEG, true);
> +
> +                       csr_read_allowed(CSR_SLWID, &trap);
> +                       if (!trap.cause) {
> +                               __sbi_hart_update_extension(hfeatures,
> +                                                           SBI_HART_EXT_SSWID, true);
> +                       }
> +               }
> +
> +               csr_write(CSR_MWIDDELEG, old_mwiddeleg);
> +
> +skip_smwiddeleg:
> +               ;
> +       }
>
>  #undef __check_ext_csr
>
> --
> 2.43.7
>
>
> --
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