lib: sbi: Introduce hart protection abstraction

Currently, PMP and ePMP are the only hart protection mechanisms
available in OpenSBI but new protection mechanisms (such as Smmpt)
will be added in the near future.

To allow multiple hart protection mechanisms, introduce hart
protection abstraction and related APIs.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Link: https://lore.kernel.org/r/20251209135235.423391-3-apatel@ventanamicro.com
Signed-off-by: Anup Patel <anup@brainfault.org>

include/sbi/sbi_hart_protection.h

@@ -0,0 +1,100 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2025 Ventana Micro Systems Inc.
+ */
+
+#ifndef __SBI_HART_PROTECTION_H__
+#define __SBI_HART_PROTECTION_H__
+
+#include <sbi/sbi_types.h>
+#include <sbi/sbi_list.h>
+
+struct sbi_scratch;
+
+/** Representation of hart protection mechanism */
+struct sbi_hart_protection {
+	/** List head */
+	struct sbi_dlist head;
+
+	/** Name of the hart protection mechanism */
+	char name[32];
+
+	/** Ratings of the hart protection mechanism (higher is better) */
+	unsigned long rating;
+
+	/** Configure protection for current HART (Mandatory) */
+	int (*configure)(struct sbi_scratch *scratch);
+
+	/** Unconfigure protection for current HART (Mandatory) */
+	void (*unconfigure)(struct sbi_scratch *scratch);
+
+	/** Create temporary mapping to access address range on current HART (Optional) */
+	int (*map_range)(struct sbi_scratch *scratch,
+			 unsigned long base, unsigned long size);
+
+	/** Destroy temporary mapping on current HART (Optional) */
+	int (*unmap_range)(struct sbi_scratch *scratch,
+			   unsigned long base, unsigned long size);
+};
+
+/**
+ * Get the best hart protection mechanism
+ *
+ * @return pointer to best hart protection mechanism
+ */
+struct sbi_hart_protection *sbi_hart_protection_best(void);
+
+/**
+ * Register a hart protection mechanism
+ *
+ * @param hprot pointer to hart protection mechanism
+ *
+ * @return 0 on success and negative error code on failure
+ */
+int sbi_hart_protection_register(struct sbi_hart_protection *hprot);
+
+/**
+ * Unregister a hart protection mechanism
+ *
+ * @param hprot pointer to hart protection mechanism
+ */
+void sbi_hart_protection_unregister(struct sbi_hart_protection *hprot);
+
+/**
+ * Configure protection for current HART
+ *
+ * @param scratch pointer to scratch space of current HART
+ *
+ * @return 0 on success and negative error code on failure
+ */
+int sbi_hart_protection_configure(struct sbi_scratch *scratch);
+
+/**
+ * Unconfigure protection for current HART
+ *
+ * @param scratch pointer to scratch space of current HART
+ */
+void sbi_hart_protection_unconfigure(struct sbi_scratch *scratch);
+
+/**
+ * Create temporary mapping to access address range on current HART
+ *
+ * @param base base address of the temporary mapping
+ * @param size size of the temporary mapping
+ *
+ * @return 0 on success and negative error code on failure
+ */
+int sbi_hart_protection_map_range(unsigned long base, unsigned long size);
+
+/**
+ * Destroy temporary mapping to access address range on current HART
+ *
+ * @param base base address of the temporary mapping
+ * @param size size of the temporary mapping
+ *
+ * @return 0 on success and negative error code on failure
+ */
+int sbi_hart_protection_unmap_range(unsigned long base, unsigned long size);
+
+#endif /* __SBI_HART_PROTECTION_H__ */

lib/sbi/objects.mk

@@ -75,6 +75,7 @@ libsbi-objs-y += sbi_emulate_csr.o
 libsbi-objs-y += sbi_fifo.o
 libsbi-objs-y += sbi_fwft.o
 libsbi-objs-y += sbi_hart.o
+libsbi-objs-y += sbi_hart_protection.o
 libsbi-objs-y += sbi_heap.o
 libsbi-objs-y += sbi_math.o
 libsbi-objs-y += sbi_hfence.o

lib/sbi/sbi_hart_protection.c

@@ -0,0 +1,96 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2025 Ventana Micro Systems Inc.
+ */
+
+#include <sbi/sbi_error.h>
+#include <sbi/sbi_hart_protection.h>
+#include <sbi/sbi_scratch.h>
+
+static SBI_LIST_HEAD(hart_protection_list);
+
+struct sbi_hart_protection *sbi_hart_protection_best(void)
+{
+	if (sbi_list_empty(&hart_protection_list))
+		return NULL;
+
+	return sbi_list_first_entry(&hart_protection_list, struct sbi_hart_protection, head);
+}
+
+int sbi_hart_protection_register(struct sbi_hart_protection *hprot)
+{
+	struct sbi_hart_protection *pos = NULL;
+	bool found_pos = false;
+
+	if (!hprot)
+		return SBI_EINVAL;
+
+	sbi_list_for_each_entry(pos, &hart_protection_list, head) {
+		if (hprot->rating > pos->rating) {
+			found_pos = true;
+			break;
+		}
+	}
+
+	if (found_pos)
+		sbi_list_add_tail(&hprot->head, &pos->head);
+	else
+		sbi_list_add_tail(&hprot->head, &hart_protection_list);
+
+	return 0;
+}
+
+void sbi_hart_protection_unregister(struct sbi_hart_protection *hprot)
+{
+	if (!hprot)
+		return;
+
+	sbi_list_del(&hprot->head);
+}
+
+int sbi_hart_protection_configure(struct sbi_scratch *scratch)
+{
+	struct sbi_hart_protection *hprot = sbi_hart_protection_best();
+
+	if (!hprot)
+		return SBI_EINVAL;
+	if (!hprot->configure)
+		return SBI_ENOSYS;
+
+	return hprot->configure(scratch);
+}
+
+void sbi_hart_protection_unconfigure(struct sbi_scratch *scratch)
+{
+	struct sbi_hart_protection *hprot = sbi_hart_protection_best();
+
+	if (!hprot || !hprot->unconfigure)
+		return;
+
+	hprot->unconfigure(scratch);
+}
+
+int sbi_hart_protection_map_range(unsigned long base, unsigned long size)
+{
+	struct sbi_hart_protection *hprot = sbi_hart_protection_best();
+
+	if (!hprot)
+		return SBI_EINVAL;
+	if (!hprot->map_range)
+		return 0;
+
+	return hprot->map_range(sbi_scratch_thishart_ptr(), base, size);
+}
+
+int sbi_hart_protection_unmap_range(unsigned long base, unsigned long size)
+{
+	struct sbi_hart_protection *hprot = sbi_hart_protection_best();
+
+	if (!hprot)
+		return SBI_EINVAL;
+	if (!hprot->unmap_range)
+		return 0;
+
+	return hprot->unmap_range(sbi_scratch_thishart_ptr(), base, size);
+}

lib/sbi/sbi_init.c

@@ -18,6 +18,7 @@
 #include <sbi/sbi_fwft.h>
 #include <sbi/sbi_hart.h>
 #include <sbi/sbi_hartmask.h>
+#include <sbi/sbi_hart_protection.h>
 #include <sbi/sbi_heap.h>
 #include <sbi/sbi_hsm.h>
 #include <sbi/sbi_ipi.h>
@@ -74,6 +75,7 @@ static void sbi_boot_print_general(struct sbi_scratch *scratch)
 	const struct sbi_hsm_device *hdev;
 	const struct sbi_ipi_device *idev;
 	const struct sbi_timer_device *tdev;
+	const struct sbi_hart_protection *hprot;
 	const struct sbi_console_device *cdev;
 	const struct sbi_system_reset_device *srdev;
 	const struct sbi_system_suspend_device *susp_dev;
@@ -90,6 +92,9 @@ static void sbi_boot_print_general(struct sbi_scratch *scratch)
 	sbi_printf("Platform Features           : %s\n", str);
 	sbi_printf("Platform HART Count         : %u\n",
 		   sbi_platform_hart_count(plat));
+	hprot = sbi_hart_protection_best();
+	sbi_printf("Platform HART Protection    : %s\n",
+		   (hprot) ? hprot->name : "---");
 	idev = sbi_ipi_get_device();
 	sbi_printf("Platform IPI Device         : %s\n",
 		   (idev) ? idev->name : "---");