Implement PMP region load and evict operations

Add functions to dynamically load flexpages into hardware PMP
regions and evict them when no longer needed. These operations
bridge the software flexpage abstraction with hardware PMP
configuration, enabling runtime memory protection management.

Author: HeatCrab

kernel/memprot.c

@@ -68,3 +68,62 @@ fpage_t *select_victim_fpage(memspace_t *mspace)
 
     return victim;
 }
+
+/* Loads a flexpage into a PMP hardware region.
+ *
+ * @fpage : Pointer to flexpage to load
+ * @region_idx : Hardware PMP region index (0-15)
+ * Returns 0 on success, or negative error code on failure.
+ */
+int32_t pmp_load_fpage(fpage_t *fpage, uint8_t region_idx)
+{
+    if (!fpage)
+        return -1;
+
+    pmp_config_t *config = pmp_get_config();
+    if (!config)
+        return -1;
+
+    /* Configure PMP region from flexpage attributes */
+    pmp_region_t region = {
+        .addr_start = fpage->base,
+        .addr_end = fpage->base + fpage->size,
+        .permissions = fpage->rwx,
+        .priority = fpage->priority,
+        .region_id = region_idx,
+        .locked = 0,
+    };
+
+    int32_t ret = pmp_set_region(config, &region);
+    if (ret == 0) {
+        fpage->pmp_id = region_idx;
+    }
+
+    return ret;
+}
+
+/* Evicts a flexpage from its PMP hardware region.
+ *
+ * @fpage : Pointer to flexpage to evict
+ * Returns 0 on success, or negative error code on failure.
+ */
+int32_t pmp_evict_fpage(fpage_t *fpage)
+{
+    if (!fpage)
+        return -1;
+
+    /* Only evict if actually loaded into PMP */
+    if (fpage->pmp_id == 0)
+        return 0;
+
+    pmp_config_t *config = pmp_get_config();
+    if (!config)
+        return -1;
+
+    int32_t ret = pmp_disable_region(config, fpage->pmp_id);
+    if (ret == 0) {
+        fpage->pmp_id = 0;
+    }
+
+    return ret;
+}