feat: Initial PMM implementation

Introduce the foundational Physical Memory Manager (PMM) and restructure the project for modularity.
Implemented basic PMM and related memory management headers (mm/pmm.h, mm/vm.h).
Updated Makefile and build process to support new modular structure.

1 files changed, 100 insertions, 0 deletions

diff --git a/src/kernel/mm/vm.cc b/src/kernel/mm/vm.cc
new file mode 100644
index 0000000..3c14d40
--- /dev/null
+++ b/src/kernel/mm/vm.cc
@@ -0,0 +1,100 @@
+#include "kernel/mm.h"
+#include "kernel/pmm.h"
+#include "drivers/uart.h"
+#include "common/types.h"
+
+extern "C" char text_start[];
+extern "C" char text_end[];
+extern "C" char rodata_start[];
+extern "C" char rodata_end[];
+extern "C" char data_start[];
+extern "C" char kernel_end[];
+
+namespace VM
+{
+    pagetable_t kernel_pagetable;
+
+    #define PX(level, va) ((((uint64)va) >> (12 + 9 * (level))) & 0x1FF)
+    #define PA2PTE(pa) ((((uint64)pa) >> 12) << 10)
+    #define PTE2PA(pte) (((pte) >> 10) << 12)
+
+    pte_t *walk(pagetable_t pagetable, uint64 va, int alloc)
+    {
+        for (int level = 2; level > 0; level--)
+        {
+            pte_t *pte = &pagetable[PX(level, va)];
+
+            if (*pte & PTE_V)
+            {
+                pagetable = (pagetable_t)PTE2PA(*pte);
+            }
+            else
+            {
+                if (!alloc)
+                    return 0;
+
+                pagetable = (pagetable_t)PMM::alloc_page();
+                if (!pagetable)
+                    return 0;
+
+                *pte = PA2PTE(pagetable) | PTE_V;
+            }
+        }
+        return &pagetable[PX(0, va)];
+    }
+
+    int mappages(pagetable_t pagetable, uint64 va, uint64 size, uint64 pa, int perm)
+    {
+        uint64 a, last;
+        pte_t *pte;
+
+        a = (va / PGSIZE) * PGSIZE;
+        last = ((va + size - 1) / PGSIZE) * PGSIZE;
+
+        for(;;)
+        {
+            if((pte = walk(pagetable, a, 1)) == 0)
+                return -1;
+
+            if (*pte & PTE_V)
+            {
+                Drivers::uart_puts("Remap error\n");
+                return -1;
+            }
+
+            *pte = PA2PTE(pa) | perm | PTE_V;
+
+            if (a == last)
+                break;
+            a += PGSIZE;
+            pa += PGSIZE;
+        }
+        return 0;
+    }
+
+    void kvminit()
+    {
+        kernel_pagetable = (pagetable_t)PMM::alloc_page();
+
+        mappages(kernel_pagetable, 0x10000000, 0x10000, 0x10000000, PTE_R | PTE_W);
+
+        mappages(kernel_pagetable, (uint64)text_start, (uint64)text_end - (uint64)text_start,
+                 (uint64)text_start, PTE_R | PTE_X);
+
+        mappages(kernel_pagetable, (uint64)data_start, PHYSTOP - (uint64)data_start,
+                 (uint64)data_start, PTE_R | PTE_W);
+
+        mappages(kernel_pagetable, (uint64)rodata_start, (uint64)rodata_end - (uint64)rodata_start,
+                 (uint64)rodata_start, PTE_R);
+        
+    }
+    void kvminithart()
+    {
+        asm volatile("sfence.vma zero, zero");
+
+        uint64 satp_val = MAKE_SATP(kernel_pagetable);
+        asm volatile("csrw satp, %0" : : "r"(satp_val));
+
+        asm volatile("sfence.vma zero, zero");
+    }
+}
\ No newline at end of file