parallel compile, SMP, swapgs, cleanup, remove useless Reserved fields

code/kernel/mm_phys.c

@@ -101,6 +101,26 @@ bool MmInitializePhysical(const MEMORY_MAP* map, uint64_t physicalWindowBase) {
 // ---------------------------------------------------------------------------
 // Public API
 // ---------------------------------------------------------------------------
+PHYSICAL_ADDRESS MmAllocateFrameBelow(PHYSICAL_ADDRESS maxExclusive) {
+    if (maxExclusive <= PAGE_SIZE) return (PHYSICAL_ADDRESS)0;
+
+    uintptr_t flags = KeAcquireSpinlock(&gFrameStack.Lock);
+    for (size_t i = gFrameStack.Top; i > 0; i--) {
+        size_t idx = i - 1;
+        PHYSICAL_ADDRESS frame = gFrameStack.Stack[idx];
+        if (frame && frame < maxExclusive && !(frame & (PAGE_SIZE - 1))) {
+            size_t tail = gFrameStack.Top - idx - 1;
+            for (size_t j = 0; j < tail; j++)
+                gFrameStack.Stack[idx + j] = gFrameStack.Stack[idx + 1 + j];
+            gFrameStack.Top--;
+            KeReleaseSpinlock(&gFrameStack.Lock, flags);
+            return frame;
+        }
+    }
+    KeReleaseSpinlock(&gFrameStack.Lock, flags);
+    return (PHYSICAL_ADDRESS)0;
+}
+
 PHYSICAL_ADDRESS MmAllocateFrame(void) {
     uintptr_t flags = KeAcquireSpinlock(&gFrameStack.Lock);
     if (gFrameStack.Top == 0) {