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

[Yu-Chien Peter Lin]

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