sp1/amd64+vm: Fork VFR on boot

Signed-off-by: Ian Moffett <ian@mirocom.org>

usr/src/sp1/amd64/cpu/cpu_mmu.c

@@ -11,6 +11,25 @@
 
 #include <sys/cdefs.h>
 #include <mu/mmu.h>
+#include <mm/vm.h>
+#include <mm/physmem.h>
+
+/*
+ * Page-Table Entry (PTE) flags
+ *
+ * See Intel SDM Vol 3A, Section 4.5, Table 4-19
+ */
+#define PTE_ADDR_MASK   0x000FFFFFFFFFF000
+#define PTE_P           BIT(0)        /* Present */
+#define PTE_RW          BIT(1)        /* Writable */
+#define PTE_US          BIT(2)        /* User r/w allowed */
+#define PTE_PWT         BIT(3)        /* Page-level write-through */
+#define PTE_PCD         BIT(4)        /* Page-level cache disable */
+#define PTE_ACC         BIT(5)        /* Accessed */
+#define PTE_DIRTY       BIT(6)        /* Dirty (written-to page) */
+#define PTE_PS          BIT(7)        /* Page size */
+#define PTE_GLOBAL      BIT(8)        /* Global; sticky */
+#define PTE_NX          BIT(63)       /* Execute-disable */
 
 void
 mu_mmu_readvfr(struct mmu_vfr *res)
@@ -41,3 +60,32 @@ mu_mmu_writevfr(struct mmu_vfr *vfr)
         : "memory"
     );
 }
+
+status_t
+mu_mmu_forkvfr(struct mmu_vfr *vfr, struct mmu_vfr *res)
+{
+    uintptr_t dest;
+    uintptr_t *dest_p, *src_p;
+
+    if (vfr == NULL || res == NULL) {
+        return STATUS_INVALID_PARAM;
+    }
+
+    if ((dest = mm_physmem_alloc(1)) == 0) {
+        return STATUS_NO_MEMORY;
+    }
+
+    src_p = pma_to_vma((vfr->cr3 & PTE_ADDR_MASK));
+    dest_p = pma_to_vma(dest);
+
+    for (int i = 0; i < 512; ++i) {
+        if (i < 256) {
+            dest_p[i] = 0;
+        } else {
+            dest_p[i] = src_p[i];
+        }
+    }
+
+    res->cr3 = dest;
+    return STATUS_SUCCESS;
+}

usr/src/sp1/common/mm/vm_init.c

@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2026, Mirocom Laboratories
+ * All rights reserved.
+ *
+ * The following sources are CONFIDENTIAL and PROPRIETARY
+ * property of Mirocom Laboratories. Unauthorized copying,
+ * use, distribution or modification of this file, in whole
+ * and in part, is strictly prohibited without the prior written
+ * consent from Mirocom Laboratories.
+ */
+
+#include <os/knot.h>
+#include <mu/mmu.h>
+#include <lib/printf.h>
+
+#define pr_trace(fmt, ...) \
+    printf("vm: " fmt, ##__VA_ARGS__)
+
+/* Kernel virtual fuck region */
+static struct mmu_vfr kvfr;
+
+void
+mm_vm_init(void)
+{
+    struct mmu_vfr vfr;
+
+    pr_trace("forking vfr\n");
+    mu_mmu_readvfr(&vfr);
+    if (mu_mmu_forkvfr(&vfr, &kvfr) != STATUS_SUCCESS) {
+        knot("insufficient memory resources\n");
+    }
+
+    /* Update the current VFR */
+    mu_mmu_writevfr(&kvfr);
+    pr_trace("... OK\n");
+}

usr/src/sp1/common/os/main.c

@@ -15,6 +15,7 @@
 #include <lib/printf.h>
 #include <mu/cpu.h>
 #include <mm/physmem.h>
+#include <mm/vm.h>
 
 #define KERNEL_VERSION "0.0.1"
 
@@ -52,6 +53,9 @@ main(void)
     /* Initialize physical memory management */
     mm_physmem_init();
 
+    /* Initialize virtual memory management */
+    mm_vm_init();
+
     printf("[*] sp1 is pre-alpha\n");
     printf("[*] knotting kernel...\n");
     knot("end of kernel reached - halting\n");

usr/src/sp1/head/mm/vm.h

@@ -24,4 +24,9 @@
 #define vma_to_pma(vma) \
     (uintptr_t)PTR_NOFFSET(vma, bpt_kload_base())
 
+/*
+ * Initialize the virtual memory management
+ */
+void mm_vm_init(void);
+
 #endif  /* !_MM_VM_H_ */

usr/src/sp1/head/mu/mmu.h

@@ -12,6 +12,8 @@
 #ifndef _MU_MMU_H_
 #define _MU_MMU_H_ 1
 
+#include <sys/status.h>
+
 /*
  * Each running SP1 process is to have a virtual fuck region
  * which logically isolates their address space with the help
@@ -33,4 +35,12 @@ void mu_mmu_readvfr(struct mmu_vfr *res);
  */
 void mu_mmu_writevfr(struct mmu_vfr *vfr);
 
+/*
+ * Fork a VFR and clear out the lower half
+ *
+ * @vfr: Virtual fuck region to fork
+ * @res: Virtual fuck region result written here
+ */
+status_t mu_mmu_forkvfr(struct mmu_vfr *vfr, struct mmu_vfr *res);
+
 #endif  /* !_MU_MMU_H_ */