[PATCH v2 5/9] lib: sbi_hart: add WID protection mechanism

[Pawandeep Oza]

On Mon, Aug 17, 2026 at 2:05 AM Yu-Chien Peter Lin <peter.lin at sifive.com> wrote:
>
> Register a WID-based hart protection mechanism that
> configures mlwid and mwiddeleg CSRs on domain entry.
> This enables the protection framework reconfigure WID
> isolation whenever domains are switched.
>
> Signed-off-by: Yu-Chien Peter Lin <peter.lin at sifive.com>
> ---
> Changes v1 -> v2:
> - Validate WID against pmlwidlist before writing mlwid CSR (Oza)
> ---
>  include/sbi/sbi_hart_worlds.h | 24 ++++++++++++
>  lib/sbi/objects.mk            |  1 +
>  lib/sbi/sbi_hart.c            |  5 +++
>  lib/sbi/sbi_hart_worlds.c     | 72 +++++++++++++++++++++++++++++++++++
>  4 files changed, 102 insertions(+)
>  create mode 100644 include/sbi/sbi_hart_worlds.h
>  create mode 100644 lib/sbi/sbi_hart_worlds.c
>
> diff --git a/include/sbi/sbi_hart_worlds.h b/include/sbi/sbi_hart_worlds.h
> new file mode 100644
> index 00000000..2bb35a7e
> --- /dev/null
> +++ b/include/sbi/sbi_hart_worlds.h
> @@ -0,0 +1,24 @@
> +/*
> + * SPDX-License-Identifier: BSD-2-Clause
> + *
> + * Copyright (c) 2026 SiFive Inc.
> + */
> +
> +#ifndef __SBI_HART_WORLDS_H__
> +#define __SBI_HART_WORLDS_H__
> +
> +struct sbi_scratch;
> +
> +/**
> + * Initialize WID hart protection for current HART
> + *
> + * Registers the WID protection mechanism if Smwid/Smlwid
> + * extensions are present.
> + *
> + * @param scratch pointer to scratch space of current HART
> + *
> + * @return 0 on success and negative error code on failure
> + */
> +int sbi_hart_worlds_init(struct sbi_scratch *scratch);
> +
> +#endif /* __SBI_HART_WORLDS_H__ */
> diff --git a/lib/sbi/objects.mk b/lib/sbi/objects.mk
> index c29c888f..ac026dec 100644
> --- a/lib/sbi/objects.mk
> +++ b/lib/sbi/objects.mk
> @@ -77,6 +77,7 @@ libsbi-objs-y += sbi_fwft.o
>  libsbi-objs-y += sbi_hart.o
>  libsbi-objs-y += sbi_hart_pmp.o
>  libsbi-objs-y += sbi_hart_protection.o
> +libsbi-objs-y += sbi_hart_worlds.o
>  libsbi-objs-y += sbi_heap.o
>  libsbi-objs-y += sbi_math.o
>  libsbi-objs-y += sbi_hfence.o
> diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c
> index 29856c0f..e92f0af3 100644
> --- a/lib/sbi/sbi_hart.c
> +++ b/lib/sbi/sbi_hart.c
> @@ -17,6 +17,7 @@
>  #include <sbi/sbi_error.h>
>  #include <sbi/sbi_hart.h>
>  #include <sbi/sbi_hart_pmp.h>
> +#include <sbi/sbi_hart_worlds.h>
>  #include <sbi/sbi_platform.h>
>  #include <sbi/sbi_pmu.h>
>  #include <sbi/sbi_string.h>
> @@ -762,6 +763,10 @@ int sbi_hart_init(struct sbi_scratch *scratch, bool cold_boot)
>                 rc = sbi_hart_pmp_init(scratch);
>                 if (rc)
>                         return rc;
> +
> +               rc = sbi_hart_worlds_init(scratch);
> +               if (rc)
> +                       return rc;
>         }
>
>         return sbi_hart_reinit(scratch);
> diff --git a/lib/sbi/sbi_hart_worlds.c b/lib/sbi/sbi_hart_worlds.c
> new file mode 100644
> index 00000000..d9d69b07
> --- /dev/null
> +++ b/lib/sbi/sbi_hart_worlds.c
> @@ -0,0 +1,72 @@
> +/*
> + * SPDX-License-Identifier: BSD-2-Clause
> + *
> + * Copyright (c) 2026 SiFive Inc.
> + */
> +
> +#include <sbi/riscv_encoding.h>
> +#include <sbi/sbi_console.h>
> +#include <sbi/sbi_domain.h>
> +#include <sbi/sbi_error.h>
> +#include <sbi/sbi_hart.h>
> +#include <sbi/sbi_hart_protection.h>
> +#include <sbi/sbi_hart_worlds.h>
> +#include <sbi/sbi_scratch.h>
> +
> +static int sbi_hart_worlds_configure(struct sbi_scratch *scratch,
> +                                    struct sbi_domain *dom)
> +{
> +       struct sbi_hart_features *hf = sbi_hart_features_ptr(scratch);
> +       bool wid_found = true;
> +       u32 wid_val = 0;
> +
> +       if (!sbi_hart_has_extension(scratch, SBI_HART_EXT_SMLWID))
> +               return 0;
> +
> +       if (dom->has_wid) {
> +               wid_val = dom->wid;
> +       } else if (sbi_hart_has_extension(scratch, SBI_HART_EXT_SMWID)) {
> +               wid_val = csr_read(CSR_MWID) & ~MWID_LOCK;
> +       } else if (hf->has_pmwid) {
> +               wid_val = hf->pmwid;
> +       } else {
> +               /*
> +                * Smlwid present but no WID source. Without writing
> +                * mlwid, the hardware reset value is used which may
> +                * cause a software-check exception on lower-privilege
> +                * mode entry.
> +                */
> +               wid_found = false;
> +       }
> +
> +       if (wid_found) {
> +               if (hf->has_pmlwidlist &&
> +                   !(hf->pmlwidlist & BIT_ULL(wid_val))) {
> +                       sbi_printf("%s: domain wid %u not in pmlwidlist\n",
> +                                  __func__, wid_val);
> +                       return SBI_EINVAL;
> +               }
> +               csr_write(CSR_MLWID, wid_val);
> +       }
> +
> +       if (sbi_hart_has_extension(scratch, SBI_HART_EXT_SMWIDDELEG))
> +               csr_write(CSR_MWIDDELEG, dom->widdeleg);
> +
> +       return 0;
> +}
> +
> +static struct sbi_hart_protection wid_protection = {
> +       .name           = "wid",
> +       .rating         = 100,
> +       .type           = SBI_HART_PROTECTION_TYPE_ID,
> +       .configure      = sbi_hart_worlds_configure,
> +       .unconfigure    = NULL
> +};
> +
> +int sbi_hart_worlds_init(struct sbi_scratch *scratch)
> +{
> +       if (!sbi_hart_has_extension(scratch, SBI_HART_EXT_SMLWID))
> +               return 0;
> +
> +       return sbi_hart_protection_register(&wid_protection);
> +}
> --
> 2.43.7
>

Oza: except the part that if you decide to remove all the boolenas and
figure out from the wid , widlist itslef if that valid or not.

Reviewed-by: Pawandeep Oza <pawandeep.oza at oss.qualcomm.com>