[PATCH v2 5/9] lib: sbi_hart: add WID protection mechanism
Yu-Chien Peter Lin
peter.lin at sifive.com
Thu Sep 24 01:24:16 PDT 2026
Hi Oza,
On Thu, Sep 03, 2026 at 02:52:51PM -0700, Pawandeep Oza wrote:
> 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>
If the rationale I provided in PATCH2 is sound, I would keep the
code here as is.
Thanks,
Peter Lin
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