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maksw committed 2026-04-30 23:52:46 +02:00
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code/kernel/mm_virt.c
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// mm_virt.c - virtual memory manager
//
// Page tables:
// One PML4 shared by all processes.
// Upper half (bit 47 set) has U/S = 0 - ring-3 access always faults.
// Lower half pages are PAGE_USER.
//
// Kernel pool:
// A boundary-tag (header + footer) free-list allocator starting at POOL_BASE.
// Pages are committed on demand from the PMM.
//
// User heap:
// A single best-fit free list in the lower half.
// Backed on demand from the PMM. No per-process heaps.
#include "mm_virt.h"
#include "ke_spinlock.h"
#include <string.h>
#include <stddef.h>
// ---------------------------------------------------------------------------
// Helpers - physical window access
// ---------------------------------------------------------------------------
static uint64_t gPhysBase = PHYS_MAP_BASE;
static inline void* PhysToVirt(PHYSICAL_ADDRESS p) {
return (void *)(p + gPhysBase);
}
static inline uint64_t* PtePtr(PHYSICAL_ADDRESS tablePhys, unsigned idx) {
return (uint64_t *)PhysToVirt(tablePhys) + idx;
}
// ---------------------------------------------------------------------------
// PML4 / page-table helpers
// ---------------------------------------------------------------------------
static PHYSICAL_ADDRESS gPml4Phys = 0;
// Extract the page-table index for each level from a virtual address.
#define PML4_IDX(va) (((va) >> 39) & 0x1FF)
#define PDPT_IDX(va) (((va) >> 30) & 0x1FF)
#define PDT_IDX(va) (((va) >> 21) & 0x1FF)
#define PT_IDX(va) (((va) >> 12) & 0x1FF)
// Ensure a page-table entry at 'parentPhys[index]' points to a child table.
// Allocates and zeros a new frame if the entry is not present.
// Returns the physical address of the child table, or 0 on OOM.
static PHYSICAL_ADDRESS EnsureTable(PHYSICAL_ADDRESS parentPhys,
unsigned index, uint64_t extraFlags) {
uint64_t* entry = PtePtr(parentPhys, index);
if (*entry & PAGE_PRESENT) {
*entry |= extraFlags;
return* entry & ~0xFFFULL;
}
PHYSICAL_ADDRESS childPhys = MmAllocateFrame();
if (!childPhys) return 0;
memset(PhysToVirt(childPhys), 0, PAGE_SIZE);
*entry = childPhys | PAGE_PRESENT | PAGE_WRITE | extraFlags;
return childPhys;
}
// ---------------------------------------------------------------------------
// Public mapping
// ---------------------------------------------------------------------------
KSTATUS MmMapPage(uintptr_t virt, PHYSICAL_ADDRESS phys, uint64_t flags) {
unsigned userFlag = (flags & PAGE_USER) ? PAGE_USER : 0;
PHYSICAL_ADDRESS pdpt = EnsureTable(gPml4Phys, PML4_IDX(virt), userFlag);
if (!pdpt) return STATUS_NO_MEMORY;
PHYSICAL_ADDRESS pdt = EnsureTable(pdpt, PDPT_IDX(virt), userFlag);
if (!pdt) return STATUS_NO_MEMORY;
PHYSICAL_ADDRESS pt = EnsureTable(pdt, PDT_IDX(virt), userFlag);
if (!pt) return STATUS_NO_MEMORY;
uint64_t* pte = PtePtr(pt, PT_IDX(virt));
*pte = phys | flags;
__invlpg((void *)virt);
return STATUS_SUCCESS;
}
KSTATUS MmUnmapPage(uintptr_t virt) {
uint64_t* e4 = PtePtr(gPml4Phys, PML4_IDX(virt));
if (!(*e4 & PAGE_PRESENT)) return STATUS_NOT_FOUND;
uint64_t* e3 = PtePtr(*e4 & ~0xFFFULL, PDPT_IDX(virt));
if (!(*e3 & PAGE_PRESENT)) return STATUS_NOT_FOUND;
uint64_t* e2 = PtePtr(*e3 & ~0xFFFULL, PDT_IDX(virt));
if (!(*e2 & PAGE_PRESENT)) return STATUS_NOT_FOUND;
uint64_t* pte = PtePtr(*e2 & ~0xFFFULL, PT_IDX(virt));
*pte = 0;
__invlpg((void *)virt);
return STATUS_SUCCESS;
}
KSTATUS MmSetPageProtect(uintptr_t virt, size_t size, uint64_t flags) {
if (!size) return STATUS_SUCCESS;
// Round down to page boundary, round size up.
uintptr_t base = virt & PAGE_MASK;
uintptr_t end = (virt + size + PAGE_SIZE - 1) & PAGE_MASK;
for (uintptr_t va = base; va < end; va += PAGE_SIZE) {
uint64_t* e4 = PtePtr(gPml4Phys, PML4_IDX(va));
if (!(*e4 & PAGE_PRESENT)) return STATUS_NOT_FOUND;
uint64_t* e3 = PtePtr(*e4 & ~0xFFFULL, PDPT_IDX(va));
if (!(*e3 & PAGE_PRESENT)) return STATUS_NOT_FOUND;
uint64_t* e2 = PtePtr(*e3 & ~0xFFFULL, PDT_IDX(va));
if (!(*e2 & PAGE_PRESENT)) return STATUS_NOT_FOUND;
uint64_t* pte = PtePtr(*e2 & ~0xFFFULL, PT_IDX(va));
if (!(*pte & PAGE_PRESENT)) return STATUS_NOT_FOUND;
// Preserve the physical address, replace everything else.
PHYSICAL_ADDRESS phys = *pte & ~0xFFFULL & ~PAGE_NX;
*pte = phys | flags;
__invlpg((void *)va);
}
return STATUS_SUCCESS;
}
PHYSICAL_ADDRESS MmGetPhysicalAddress(uintptr_t virt) {
if (!gPml4Phys) return 0; // Not initialized
uint64_t pml4_idx = (virt >> 39) & 0x1FF;
uint64_t pdpt_idx = (virt >> 30) & 0x1FF;
uint64_t pd_idx = (virt >> 21) & 0x1FF;
uint64_t pt_idx = (virt >> 12) & 0x1FF;
uint64_t* pml4 = PhysToVirt(gPml4Phys);
if (!(pml4[pml4_idx] & PAGE_PRESENT)) return 0;
uint64_t* pdpt = PhysToVirt(pml4[pml4_idx] & ~0xFFFULL);
if (!(pdpt[pdpt_idx] & PAGE_PRESENT)) return 0;
// Check for 1GB huge pages (bit 7 - PS)
if (pdpt[pdpt_idx] & 0x80) {
return (pdpt[pdpt_idx] & 0x000FFFFFC0000000ULL) + (virt & 0x3FFFFFFF);
}
uint64_t* pd = PhysToVirt(pdpt[pdpt_idx] & ~0xFFFULL);
if (!(pd[pd_idx] & PAGE_PRESENT)) return 0;
// Check for 2MB huge pages (bit 7 - PS)
if (pd[pd_idx] & 0x80) {
return (pd[pd_idx] & 0x000FFFFFFFE00000ULL) + (virt & 0x1FFFFF);
}
uint64_t* pt = PhysToVirt(pd[pd_idx] & ~0xFFFULL);
if (!(pt[pt_idx] & PAGE_PRESENT)) return 0;
// Extract the physical frame and add the offset within the page
return (pt[pt_idx] & ~0xFFFULL) + (virt & 0xFFF);
}
// ---------------------------------------------------------------------------
// Boundary-tag allocator (used for both pool and user heap)
// ---------------------------------------------------------------------------
// Each allocation has a BLOCK_HDR immediately before the user data, and a
// BLOCK_FTR immediately after. Both carry the block size and a 'free' flag.
// This allows O(1) coalescing of adjacent free blocks.
#define BLOCK_MAGIC 0xB10CB10CUL
typedef struct BLOCK_HDR {
uint32_t Magic;
uint32_t Free; // 1 = free, 0 = used
size_t Size; // usable bytes (excludes header + footer)
struct BLOCK_HDR* PrevFree;
struct BLOCK_HDR* NextFree;
} BLOCK_HDR;
typedef struct BLOCK_FTR {
size_t Size;
uint32_t Free;
uint32_t Magic;
} BLOCK_FTR;
#define HDR_SIZE (sizeof(BLOCK_HDR))
#define FTR_SIZE (sizeof(BLOCK_FTR))
#define OVERHEAD (HDR_SIZE + FTR_SIZE)
#define MIN_BLOCK (OVERHEAD + sizeof(void*))
static inline BLOCK_FTR* HdrToFtr(BLOCK_HDR* h) {
return (BLOCK_FTR *)((char *)h + HDR_SIZE + h->Size);
}
static inline BLOCK_HDR* FtrToHdr(BLOCK_FTR* f) {
return (BLOCK_HDR *)((char *)f - HDR_SIZE - f->Size);
}
static inline BLOCK_HDR* NextBlock(BLOCK_HDR* h) {
return (BLOCK_HDR *)((char *)h + HDR_SIZE + h->Size + FTR_SIZE);
}
static inline BLOCK_FTR* PrevFtr(BLOCK_HDR* h) {
return (BLOCK_FTR *)((char *)h - FTR_SIZE);
}
typedef struct HEAP {
BLOCK_HDR* FreeList; // doubly-linked list of free blocks
uintptr_t Start; // virtual base of the arena
uintptr_t Brk; // current committed end (page-aligned)
uintptr_t Limit; // hard upper bound
uint64_t MapFlags; // PAGE_* flags for new committed pages
SPINLOCK Lock;
} HEAP;
// Extend heap by at least 'need' bytes (rounded up to page boundary).
static int HeapGrow(HEAP* h, size_t need) {
size_t grow = (need + PAGE_SIZE - 1) & ~(PAGE_SIZE - 1);
if (h->Brk + grow > h->Limit) return 0;
for (uintptr_t va = h->Brk; va < h->Brk + grow; va += PAGE_SIZE) {
PHYSICAL_ADDRESS frame = MmAllocateFrame();
if (!frame) return 0;
if (!KSUCCESS(MmMapPage(va, frame, h->MapFlags))) {
MmFreeFrame(frame);
return 0;
}
memset((void *)va, 0, PAGE_SIZE);
}
// Make the new pages a single free block.
BLOCK_HDR* blk = (BLOCK_HDR *)h->Brk;
blk->Magic = BLOCK_MAGIC;
blk->Free = 1;
blk->Size = grow - OVERHEAD;
blk->PrevFree = (BLOCK_HDR *)0;
blk->NextFree = h->FreeList;
if (h->FreeList) h->FreeList->PrevFree = blk;
h->FreeList = blk;
HdrToFtr(blk)->Magic = BLOCK_MAGIC;
HdrToFtr(blk)->Free = 1;
HdrToFtr(blk)->Size = blk->Size;
h->Brk += grow;
return 1;
}
// Unlink a free block from the free list.
static void FreeListRemove(HEAP* h, BLOCK_HDR* blk) {
if (blk->PrevFree) blk->PrevFree->NextFree = blk->NextFree;
else h->FreeList = blk->NextFree;
if (blk->NextFree) blk->NextFree->PrevFree = blk->PrevFree;
blk->PrevFree = blk->NextFree = (BLOCK_HDR *)0;
}
static void* HeapAlloc(HEAP* h, size_t size) {
if (!size) return (void *)0;
size = (size + 7) & ~7ULL; // 8-byte align
KeAcquireSpinlock(&h->Lock);
// Best-fit search.
BLOCK_HDR* best = (BLOCK_HDR *)0;
for (BLOCK_HDR* cur = h->FreeList; cur; cur = cur->NextFree) {
if (cur->Size >= size) {
if (!best || cur->Size < best->Size) best = cur;
if (best->Size == size) break;
}
}
if (!best) {
if (!HeapGrow(h, size + OVERHEAD)) {
KeReleaseSpinlock(&h->Lock);
return (void *)0;
}
// Re-search; HeapGrow inserted at the front.
best = h->FreeList;
while (best && best->Size < size) best = best->NextFree;
if (!best) {
KeReleaseSpinlock(&h->Lock);
return (void *)0;
}
}
FreeListRemove(h, best);
// Split the block if the remainder is big enough.
if (best->Size >= size + OVERHEAD + sizeof(void*)) {
BLOCK_HDR* rem = (BLOCK_HDR *)((char *)best + HDR_SIZE + size + FTR_SIZE);
rem->Magic = BLOCK_MAGIC;
rem->Free = 1;
rem->Size = best->Size - size - OVERHEAD;
rem->PrevFree = (BLOCK_HDR *)0;
rem->NextFree = h->FreeList;
if (h->FreeList) h->FreeList->PrevFree = rem;
h->FreeList = rem;
HdrToFtr(rem)->Magic = BLOCK_MAGIC;
HdrToFtr(rem)->Free = 1;
HdrToFtr(rem)->Size = rem->Size;
best->Size = size;
}
best->Free = 0;
HdrToFtr(best)->Free = 0;
HdrToFtr(best)->Magic = BLOCK_MAGIC;
HdrToFtr(best)->Size = best->Size;
KeReleaseSpinlock(&h->Lock);
return (char *)best + HDR_SIZE;
}
static void HeapFree(HEAP* h, void* ptr) {
if (!ptr) return;
BLOCK_HDR* blk = (BLOCK_HDR *)((char *)ptr - HDR_SIZE);
if (blk->Magic != BLOCK_MAGIC || blk->Free) return; // double-free / corrupt
KeAcquireSpinlock(&h->Lock);
blk->Free = 1;
// Coalesce with next block if it is free.
BLOCK_HDR* next = NextBlock(blk);
if ((uintptr_t)next < h->Brk && next->Magic == BLOCK_MAGIC && next->Free) {
FreeListRemove(h, next);
blk->Size += OVERHEAD + next->Size;
HdrToFtr(blk)->Size = blk->Size;
HdrToFtr(blk)->Magic = BLOCK_MAGIC;
HdrToFtr(blk)->Free = 1;
}
// Coalesce with previous block if it is free.
if ((uintptr_t)blk > h->Start) {
BLOCK_FTR* prevFtr = PrevFtr(blk);
if (prevFtr->Magic == BLOCK_MAGIC && prevFtr->Free) {
BLOCK_HDR* prev = FtrToHdr(prevFtr);
FreeListRemove(h, prev);
prev->Size += OVERHEAD + blk->Size;
HdrToFtr(prev)->Size = prev->Size;
HdrToFtr(prev)->Magic = BLOCK_MAGIC;
HdrToFtr(prev)->Free = 1;
blk = prev;
}
}
// Insert at head of free list.
blk->PrevFree = (BLOCK_HDR *)0;
blk->NextFree = h->FreeList;
if (h->FreeList) h->FreeList->PrevFree = blk;
h->FreeList = blk;
HdrToFtr(blk)->Free = 1;
HdrToFtr(blk)->Magic = BLOCK_MAGIC;
KeReleaseSpinlock(&h->Lock);
}
static void* HeapRealloc(HEAP* h, void* ptr, size_t new_size) {
// If ptr is NULL, realloc acts like malloc
if (!ptr) {
return HeapAlloc(h, new_size);
}
// If size is 0, realloc acts like free
if (new_size == 0) {
HeapFree(h, ptr);
return (void*)0;
}
// Retrieve the header of the existing block
BLOCK_HDR* blk = (BLOCK_HDR *)((char *)ptr - HDR_SIZE);
// Sanity checks to prevent operating on corrupted or already-freed pointers
if (blk->Magic != BLOCK_MAGIC || blk->Free) {
return (void*)0;
}
// Align the requested size (matches HeapAlloc 8-byte alignment)
size_t aligned_size = (new_size + 7) & ~7ULL;
// If the current block is already big enough, we can reuse it in-place.
// (Note: To save space, you could optionally split the block here if
// the new size is significantly smaller, similar to HeapAlloc's logic).
if (blk->Size >= aligned_size) {
return ptr;
}
// The block is too small. Allocate a new, larger block.
void* new_ptr = HeapAlloc(h, aligned_size);
if (!new_ptr) {
return (void*)0; // Out of memory, original block is left untouched
}
// Copy the old data to the new block.
// We only copy up to the old block's usable size.
memcpy(new_ptr, ptr, blk->Size);
// Free the old block
HeapFree(h, ptr);
return new_ptr;
}
// ---------------------------------------------------------------------------
// Kernel pool
// ---------------------------------------------------------------------------
static HEAP gPoolHeap;
// ---------------------------------------------------------------------------
// User heap
// ---------------------------------------------------------------------------
static HEAP gUserHeap;
// ---------------------------------------------------------------------------
// Module init
// ---------------------------------------------------------------------------
void MmInitializeVirtual(PHYSICAL_ADDRESS bootPml4Phys, size_t poolSize) {
gPml4Phys = bootPml4Phys;
// Kernel pool heap.
gPoolHeap.FreeList = (BLOCK_HDR *)0;
gPoolHeap.Start = POOL_BASE;
gPoolHeap.Brk = POOL_BASE;
gPoolHeap.Limit = POOL_LIMIT;
gPoolHeap.MapFlags = PAGE_PRESENT | PAGE_WRITE | PAGE_NX;
gPoolHeap.Lock = (SPINLOCK)SPINLOCK_INIT;
// Pre-commit the requested pool size.
if (poolSize) {
poolSize = (poolSize + PAGE_SIZE - 1) & ~(PAGE_SIZE - 1);
HeapGrow(&gPoolHeap, poolSize);
}
// User heap.
gUserHeap.FreeList = (BLOCK_HDR *)0;
gUserHeap.Start = USER_BASE;
gUserHeap.Brk = USER_BASE;
gUserHeap.Limit = USER_LIMIT;
gUserHeap.MapFlags = PAGE_PRESENT | PAGE_WRITE | PAGE_USER;
gUserHeap.Lock = (SPINLOCK)SPINLOCK_INIT;
}
void MmActivate(void) {
__writecr3(gPml4Phys);
}
// ---------------------------------------------------------------------------
// Public pool API
// ---------------------------------------------------------------------------
void* MmAllocatePool(size_t size) { return HeapAlloc(&gPoolHeap, size); }
void MmFreePool(void* ptr) { HeapFree(&gPoolHeap, ptr); }
void* MmReallocatePool(void* ptr, size_t newSize) { return HeapRealloc(&gPoolHeap, ptr, newSize); }
// ---------------------------------------------------------------------------
// Public user heap API
// ---------------------------------------------------------------------------
void* MmAllocateUserMemory(size_t size) { return HeapAlloc(&gUserHeap, size); }
void MmFreeUserMemory(void* ptr, size_t size) { (void)size; HeapFree(&gUserHeap, ptr); }
void* MmReallocateUserMemory(void* ptr, size_t newSize) { return HeapRealloc(&gUserHeap, ptr, newSize); }