move keyboard and mouse out of HAL into a standalone ps2.sys driver, implement usb stack with xhci controller discovery, hid keyboard/mouse, and bulk-only mass storage, add pci msi support with capability chain walking and software irq vector allocation (slots 16-23), rewrite user virtual memory as a USER_VA_REGION descriptor arena with per-process ownership tracking and guard page support, replacing the old bump allocator and top-down image region, add MmCreateUserRegion/MmDestroyAllUserRegions so process teardown reclaims all user va in one pass, allocate a pool-backed shadow framebuffer in hal_screen to fix cursor tearing and scroll corruption, reserve ap trampoline page below 1mb in uefi bootloader before boot services exit, rewrite memset/memcpy/memmove/memcmp with __stosq/__movsq intrinsics, promote driver flag literals to macros and add multi-tu STANDALONE_DRIVERS table to build.c, split rtl8139/rtl816x into header+source, rename KbReadScancode to KbReadKey, improve page fault output with MmDebugDescribeAddress and user region dump, fix %p to %016llX throughout.

code/kernel/mm_phys.c

@@ -101,27 +101,48 @@ 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;
+static PHYSICAL_ADDRESS KiPopFrameAtIndexLocked(size_t idx) {
+    PHYSICAL_ADDRESS frame = gFrameStack.Stack[idx];
+    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--;
+    return frame;
+}
+
+PHYSICAL_ADDRESS MmAllocateFrameInRange(PHYSICAL_ADDRESS minInclusive,
+                                        PHYSICAL_ADDRESS maxExclusive) {
+    minInclusive = (minInclusive + PAGE_SIZE - 1) & PAGE_MASK;
+    maxExclusive &= PAGE_MASK;
+
+    if (maxExclusive <= minInclusive)
+        return (PHYSICAL_ADDRESS)0;
 
     uintptr_t flags = KeAcquireSpinlock(&gFrameStack.Lock);
+
+    // Search high-to-low within the requested window.  For low-memory users
+    // such as the AP trampoline this naturally prefers the traditional
+    // 0x70000-0x9f000 area and avoids consuming lower real-mode space first.
     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--;
+        if (frame >= minInclusive && frame < maxExclusive &&
+            !(frame & (PAGE_SIZE - 1))) {
+            frame = KiPopFrameAtIndexLocked(idx);
             KeReleaseSpinlock(&gFrameStack.Lock, flags);
             return frame;
         }
     }
+
     KeReleaseSpinlock(&gFrameStack.Lock, flags);
     return (PHYSICAL_ADDRESS)0;
 }
 
-PHYSICAL_ADDRESS MmAllocateFrame(void) {
+PHYSICAL_ADDRESS MmAllocateFrameBelow(PHYSICAL_ADDRESS maxExclusive) {
+    return MmAllocateFrameInRange(PAGE_SIZE, maxExclusive);
+}
+
+__declspec(dllexport) PHYSICAL_ADDRESS MmAllocateFrame(void) {
     uintptr_t flags = KeAcquireSpinlock(&gFrameStack.Lock);
     if (gFrameStack.Top == 0) {
         KeReleaseSpinlock(&gFrameStack.Lock, flags);