refactor(memory): complete PMM/VMM/LMM rewrite - bitmap allocators, bug fixes, hardening

PMM Rewrite:
- Replace ~8KB record array with compact bitmaps
  (PhysPresent/PhysAlloc/PhysScanned, 128B each)
- Add PhysOwner[0..1023] for per-block ownership tracking
- new_block: O(1) amortised via NextFreeHint + dword-level BSF scan,
  returns 0 as OOM sentinel
- free_block: O(1) direct bit clear with double-free detection
- alloc_block: validates PhysPresent and PhysAlloc bits before allocation
- Add pmm_free_blocks/pmm_total_blocks stats functions

VMM Correctness Fixes:
- Fix free_page block extraction (Address SHR 10, was using
  raw Address field)
- Fix invlpg operand (use virtual address, was passing PDE index)
- Clear PDE entry on free_page before returning block to PMM
- Remove map_page double-write (delegate to map_page_ex only)
- Add OOM propagation (new_page returns false if PMM returns 0)
- Fix missing pop_trace in new_page error path

LMM Rewrite:
- Replace per-entry record array with bitmap allocator
  (93% vs 43% page efficiency)
- Layout: Header(24B) + Bitmap(64512B) + Padding + Data at 0x10000
- SIZE_PREFIX=16 for 16-byte aligned returns (SSE MOVAPS requirement)
- Next-fit bitmap scan with roving hint (NextFree) and dword-level
  fast skip
- Large alloc sentinel (LARGE_ALLOC_MAGIC=$FFFFFFFE) so kfree detects
  klalloc'd memory
- Implement klfree (was previously a no-op - pages could never
  be returned)
- Implement try_release_page (return fully-free heap pages to VMM/PMM)
- Fix interrupt safety: stack-balanced pushfd/cli/pop +
  restore_if (sti only)
  Fixes Bad TSS caused by popfd restoring dangerous EFLAGS bits (NT, IOPL)
- Zero memory via rep stosd instead of byte-by-byte loop

Hardening:
- kalloc OOM now triggers BSOD instead of returning nil
  (90% of callers don't check)
- Double-free detection in kfree (verify bitmap bits set before clearing)
- Guard bytes ({$IFDEF DEBUG_LMM}): $DEADBEEF sentinel for buffer overrun detection
- kpalloc: bounds check (block >= 1024 -> GPF) + syslog MMIO mapping audit log

Observability:
- Add MEMINFO command as src/prog/meminfo.pas (moved from inline kernel.pas)
- Displays multiboot memory, PMM block stats, LMM heap stats
- Register via progmanager.pas following standard prog pattern

Files changed:
- src/pmemorymanager.pas
- src/vmemorymanager.pas
- src/lmemorymanager.pas
- src/kernel.pas
- src/progmanager.pas
- src/prog/meminfo.pas

src/kernel.pas

@@ -74,23 +74,6 @@ procedure kmain(mbinfo: Pmultiboot_info_t; mbmagic: uint32); stdcall;
  
 implementation
 
-procedure terminal_command_meminfo(params : PParamList; stdin_buf, stdout_buf, stderr_buf : POutBuf);
-begin
-    push_trace('kernel.terminal_command_meminfo');
-
-    stdio.bufWriteStr(stdout_buf, 'Lower Memory = ');
-    stdio.bufWriteInt(stdout_buf, multibootinfo^.mem_lower);
-    stdio.bufWriteStrLn(stdout_buf, 'KB');
-    stdio.bufWriteStr(stdout_buf, 'Higher Memory = ');
-    stdio.bufWriteInt(stdout_buf, multibootinfo^.mem_upper);
-    stdio.bufWriteStrLn(stdout_buf, 'KB');
-    stdio.bufWriteStr(stdout_buf, 'Total Memory = ');
-    stdio.bufWriteInt(stdout_buf, ((multibootinfo^.mem_upper + 1000) div 1024) + 1);
-    stdio.bufWriteStrLn(stdout_buf, 'MB');
-
-    pop_trace;
-end;
-
 procedure terminal_command_bsod(params : PParamList; stdin_buf, stdout_buf, stderr_buf : POutBuf);
 begin
     push_trace('kernel.terminal_command_bsod');
@@ -183,7 +166,6 @@ begin
 
      { Stdio Init }
      stdio.init();
-     stdio.registerCommand('MEMINFO', @terminal_command_meminfo, 'Print Simple Memory Information.');
      stdio.registerCommand('BSOD', @terminal_command_bsod, 'Force a Panic Screen.');
 
      tss.init();

src/prog/meminfo.pas

@@ -0,0 +1,83 @@
+//  Copyright 2021 Kieron Morris
+//
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//  http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Unless required by applicable law or agreed to in writing, software
+//  distributed under the License is distributed on an "AS IS" BASIS,
+//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+//  limitations under the License.
+
+{ 
+	Prog->meminfo - Print memory statistics (PMM / LMM).
+	
+	@author(Kieron Morris <[email protected]>)
+}
+unit meminfo;
+
+interface
+
+uses
+    stdio, multiboot, pmemorymanager, lmemorymanager, tracer;
+
+procedure init();
+
+implementation
+
+procedure run(Params : PParamList; stdin_buf, stdout_buf, stderr_buf : POutBuf);
+var
+    pmm_total, pmm_free, pmm_used : uint32;
+    lmm_pages, lmm_free           : uint32;
+begin
+    { Multiboot memory info }
+    stdio.bufWriteStrLn(stdout_buf, '--- Multiboot ---');
+    stdio.bufWriteStr(stdout_buf, 'Lower Memory  : ');
+    stdio.bufWriteInt(stdout_buf, multibootinfo^.mem_lower);
+    stdio.bufWriteStrLn(stdout_buf, ' KB');
+    stdio.bufWriteStr(stdout_buf, 'Upper Memory  : ');
+    stdio.bufWriteInt(stdout_buf, multibootinfo^.mem_upper);
+    stdio.bufWriteStrLn(stdout_buf, ' KB');
+    stdio.bufWriteStr(stdout_buf, 'Total Memory  : ');
+    stdio.bufWriteInt(stdout_buf, ((multibootinfo^.mem_upper + 1000) div 1024) + 1);
+    stdio.bufWriteStrLn(stdout_buf, ' MB');
+
+    { PMM stats }
+    stdio.bufWriteStrLn(stdout_buf, '--- PMM (4 MB blocks) ---');
+    pmm_total := pmemorymanager.pmm_total_blocks;
+    pmm_free  := pmemorymanager.pmm_free_blocks;
+    pmm_used  := pmm_total - pmm_free;
+    stdio.bufWriteStr(stdout_buf, 'Total Blocks  : ');
+    stdio.bufWriteIntLn(stdout_buf, pmm_total);
+    stdio.bufWriteStr(stdout_buf, 'Free Blocks   : ');
+    stdio.bufWriteIntLn(stdout_buf, pmm_free);
+    stdio.bufWriteStr(stdout_buf, 'Used Blocks   : ');
+    stdio.bufWriteIntLn(stdout_buf, pmm_used);
+    stdio.bufWriteStr(stdout_buf, 'Free Physical : ');
+    stdio.bufWriteInt(stdout_buf, pmm_free * 4);
+    stdio.bufWriteStrLn(stdout_buf, ' MB');
+
+    { LMM heap stats }
+    stdio.bufWriteStrLn(stdout_buf, '--- LMM (Heap) ---');
+    lmm_pages := lmemorymanager.lmm_page_count;
+    lmm_free  := lmemorymanager.lmm_total_free;
+    stdio.bufWriteStr(stdout_buf, 'Heap Pages    : ');
+    stdio.bufWriteIntLn(stdout_buf, lmm_pages);
+    stdio.bufWriteStr(stdout_buf, 'Heap Size     : ');
+    stdio.bufWriteInt(stdout_buf, lmm_pages * 4);
+    stdio.bufWriteStrLn(stdout_buf, ' MB');
+    stdio.bufWriteStr(stdout_buf, 'Heap Free     : ');
+    stdio.bufWriteInt(stdout_buf, lmm_free div 1024);
+    stdio.bufWriteStrLn(stdout_buf, ' KB');
+end;
+
+procedure init();
+begin
+    tracer.push_trace('meminfo.init');
+    stdio.registerCommand('MEMINFO', @Run, 'Print memory statistics (PMM/LMM).');
+end;
+
+end.

src/progmanager.pas

@@ -24,7 +24,7 @@ interface
 uses
     tracer,
     //progs
-    base64_prog, md5sum, dhclient, vbeinfo;
+    base64_prog, md5sum, dhclient, vbeinfo, meminfo;
 
 { Initialize all baked-in programs }
 procedure init();
@@ -40,6 +40,7 @@ begin
     tracer.push_trace('progmanager.dhclient.init');
     dhclient.init();
     vbeinfo.init();
+    meminfo.init();
 end;
 
 end.

src/vmemorymanager.pas

@@ -159,20 +159,14 @@ end;
 
 function map_page(page_number : uint16; block : uint16) : boolean;
 var
-    addr  : ubit20;
-    page  : uint16;
     rldpd : uint32;
 
 begin
     push_trace('vmemorymanager.map_page');
-    map_page:= false; 
-    PageDirectory^[page_number].Present:= true;
-    addr:= block;
-    PageDirectory^[page_number].Address:= addr SHL 10;
-    PageDirectory^[page_number].PageSize:= true;
-    PageDirectory^[page_number].Writable:= true;
-    map_page:= map_page_ex(page_number, block, PageDirectory);
-    rldpd:= uint32(PageDirectory) - KERNEL_VIRTUAL_BASE;
+    { Delegate to map_page_ex — no redundant direct PDE writes }
+    map_page := map_page_ex(page_number, block, PageDirectory);
+    { Reload CR3 to flush TLB }
+    rldpd := uint32(PageDirectory) - KERNEL_VIRTUAL_BASE;
     asm
         mov eax, rldpd
         mov CR3, eax
@@ -201,14 +195,15 @@ var
 
 begin
     push_trace('vmemorymanager.new_page');
-    new_page:= false;
+    new_page := false;
     if not PageDirectory^[page_number].Present then begin
         if not PageDirectory^[page_number].Reserved then begin
-            block:= pmemorymanager.new_block(uint32(PageDirectory));
-            if block < 2 then begin
-                GPF;
+            block := pmemorymanager.new_block(uint32(PageDirectory));
+            if block = 0 then begin
+                { OOM — PMM has no free blocks. Return false gracefully. }
+                syslog.logln('VMM', 'ERROR: new_page failed — PMM OOM.');
             end else begin
-                new_page:= map_page(page_number, block);
+                new_page := map_page(page_number, block);
             end;
         end;
     end;
@@ -216,17 +211,15 @@ begin
 end;
 
 function page_mappable(page_number : uint16) : boolean;
-var
-    block : uint16;
-
 begin
     push_trace('vmemorymanager.page_mappable');
-    page_mappable:= false;
+    page_mappable := false;
     if not PageDirectory^[page_number].Present then begin
         if not PageDirectory^[page_number].Reserved then begin
-            page_mappable:= true;
+            page_mappable := true;
         end;
     end;
+    pop_trace;
 end;
 
 function new_page_at_address(address : uint32) : boolean;
@@ -243,14 +236,25 @@ end;
 procedure free_page(page_number : uint16);
 var
     block : uint16;
+    vaddr : uint32;
 
 begin
     push_trace('vmemorymanager.free_page');
     if PageDirectory^[page_number].Present then begin
-        block:= PageDirectory^[page_number].Address;
+        { Recover block index: Address stores (block SHL 10), so SHR 10 gives block }
+        block := PageDirectory^[page_number].Address SHR 10;
+        { Clear the PDE before invalidating }
+        PageDirectory^[page_number].Present    := false;
+        PageDirectory^[page_number].Writable   := false;
+        PageDirectory^[page_number].PageSize   := false;
+        PageDirectory^[page_number].Address    := 0;
+        { Invalidate TLB for this virtual address (invlpg needs a virtual addr) }
+        vaddr := uint32(page_number) SHL 22;
         asm
-            invlpg [page_number]
+            mov eax, vaddr
+            invlpg [eax]
         end;
+        { Return physical block to PMM }
         pmemorymanager.free_block(block, uint32(PageDirectory));
     end else begin
         GPF;