feat(mm): add page table management and on-demand mapping

include/paging.h

@@ -0,0 +1,14 @@
+#ifndef FROSTBYTE_PAGING_H
+#define FROSTBYTE_PAGING_H
+
+#include "types.h"
+
+#define pagePresent 0x1
+#define pageWrite   0x2
+#define pageUser    0x4
+
+bool pagingMap(uint64 virtualAddr, uint64 physicalAddr, uint64 flags);
+uint64 pagingResolve(uint64 virtualAddr);
+bool pagingMapUserRange(uint64 virtualAddr, uint64 size);
+
+#endif

src/paging.c

@@ -0,0 +1,114 @@
+#include "paging.h"
+#include "pmm.h"
+#include "string.h"
+
+#define entryPresent 0x1
+#define entryPageSize 0x80
+#define addressMask 0x000FFFFFFFFFF000ull
+
+static uint64 readCr3(void)
+{
+    uint64 value;
+    __asm__ volatile("mov %%cr3, %0" : "=r"(value));
+    return value;
+}
+
+static void invalidatePage(uint64 virtualAddr)
+{
+    __asm__ volatile("invlpg (%0)" : : "r"(virtualAddr) : "memory");
+}
+
+static uint64* tableFrom(uint64 entry)
+{
+    return (uint64*)(entry & addressMask);
+}
+
+static uint64* nextTable(uint64* table, uint64 index, uint64 parentFlags, bool create)
+{
+    if (table[index] & entryPresent) {
+        table[index] |= parentFlags;
+        return tableFrom(table[index]);
+    }
+
+    if (!create)
+        return nullptr;
+
+    uint64 frame = pmmAlloc();
+    if (frame == 0)
+        return nullptr;
+
+    memset((void*)frame, 0, frameSize);
+    table[index] = frame | pagePresent | pageWrite | parentFlags;
+    return (uint64*)frame;
+}
+
+bool pagingMap(uint64 virtualAddr, uint64 physicalAddr, uint64 flags)
+{
+    uint64 pml4Index = (virtualAddr >> 39) & 0x1FF;
+    uint64 pdptIndex = (virtualAddr >> 30) & 0x1FF;
+    uint64 pdIndex = (virtualAddr >> 21) & 0x1FF;
+    uint64 ptIndex = (virtualAddr >> 12) & 0x1FF;
+    uint64 parentFlags = flags & pageUser;
+
+    uint64* pml4 = tableFrom(readCr3());
+    uint64* pdpt = nextTable(pml4, pml4Index, parentFlags, true);
+    if (!pdpt)
+        return false;
+    uint64* pd = nextTable(pdpt, pdptIndex, parentFlags, true);
+    if (!pd)
+        return false;
+
+    if (pd[pdIndex] & entryPageSize)
+        return false;
+
+    uint64* pt = nextTable(pd, pdIndex, parentFlags, true);
+    if (!pt)
+        return false;
+
+    pt[ptIndex] = (physicalAddr & addressMask) | (flags & 0xFFF) | pagePresent;
+    invalidatePage(virtualAddr);
+    return true;
+}
+
+uint64 pagingResolve(uint64 virtualAddr)
+{
+    uint64 pml4Index = (virtualAddr >> 39) & 0x1FF;
+    uint64 pdptIndex = (virtualAddr >> 30) & 0x1FF;
+    uint64 pdIndex = (virtualAddr >> 21) & 0x1FF;
+    uint64 ptIndex = (virtualAddr >> 12) & 0x1FF;
+
+    uint64* pml4 = tableFrom(readCr3());
+    uint64* pdpt = nextTable(pml4, pml4Index, 0, false);
+    if (!pdpt)
+        return 0;
+    uint64* pd = nextTable(pdpt, pdptIndex, 0, false);
+    if (!pd)
+        return 0;
+    if (pd[pdIndex] & entryPageSize)
+        return (pd[pdIndex] & addressMask) + (virtualAddr & 0x1FFFFF);
+
+    uint64* pt = nextTable(pd, pdIndex, 0, false);
+    if (!pt)
+        return 0;
+    if (!(pt[ptIndex] & entryPresent))
+        return 0;
+    return (pt[ptIndex] & addressMask) + (virtualAddr & 0xFFF);
+}
+
+bool pagingMapUserRange(uint64 virtualAddr, uint64 size)
+{
+    uint64 first = virtualAddr & ~(uint64)(frameSize - 1);
+    uint64 last = (virtualAddr + size + frameSize - 1) & ~(uint64)(frameSize - 1);
+
+    for (uint64 page = first; page < last; page += frameSize) {
+        if (pagingResolve(page) != 0)
+            continue;
+        uint64 frame = pmmAlloc();
+        if (frame == 0)
+            return false;
+        if (!pagingMap(page, frame, pageUser | pageWrite))
+            return false;
+        memset((void*)page, 0, frameSize);
+    }
+    return true;
+}