[zion] Add utility to zero out a page when allocating one.

zion/memory/paging_util.cpp

@@ -24,16 +24,6 @@
 namespace {
 
 uint64_t PageAlign(uint64_t addr) { return addr & ~0xFFF; }
-uint64_t* PageAlign(uint64_t* addr) {
-  return reinterpret_cast<uint64_t*>(reinterpret_cast<uint64_t>(addr) & ~0xFFF);
-}
-
-void ZeroOutPage(uint64_t* ptr) {
-  ptr = PageAlign(ptr);
-  for (uint64_t i = 0; i < 512; i++) {
-    ptr[i] = 0;
-  }
-}
 
 uint64_t ShiftForEntryIndexing(uint64_t addr, uint64_t offset) {
   addr &= ~0xFFFF0000'00000000;
@@ -126,21 +116,18 @@ void MapPage(uint64_t cr3, uint64_t vaddr, uint64_t paddr) {
 
   uint64_t* pml4_entry = Pml4Entry(cr3, vaddr);
   if (!(*pml4_entry & PRESENT_BIT)) {
-    uint64_t page = phys_mem::AllocatePage();
+    uint64_t page = phys_mem::AllocateAndZeroPage();
     *pml4_entry = page | access_bits;
-    ZeroOutPage(PageDirectoryPointerEntry(*pml4_entry, vaddr));
   }
   uint64_t* pdp_entry = PageDirectoryPointerEntry(*pml4_entry, vaddr);
   if (!(*pdp_entry & PRESENT_BIT)) {
-    uint64_t page = phys_mem::AllocatePage();
+    uint64_t page = phys_mem::AllocateAndZeroPage();
     *pdp_entry = page | access_bits;
-    ZeroOutPage(PageDirectoryEntry(*pdp_entry, vaddr));
   }
   uint64_t* pd_entry = PageDirectoryEntry(*pdp_entry, vaddr);
   if (!(*pd_entry & PRESENT_BIT)) {
-    uint64_t page = phys_mem::AllocatePage();
+    uint64_t page = phys_mem::AllocateAndZeroPage();
     *(pd_entry) = page | access_bits;
-    ZeroOutPage(PageTableEntry(*pd_entry, vaddr));
   }
 
   uint64_t* pt_entry = PageTableEntry(*pd_entry, vaddr);
@@ -158,9 +145,7 @@ uint64_t AllocatePageIfNecessary(uint64_t addr) {
     return phys;
   }
   phys = phys_mem::AllocatePage();
-  // FIXME: Maybe move this to the physical memory allocator.
-  ZeroOutPage(
-      reinterpret_cast<uint64_t*>(boot::GetHigherHalfDirectMap() + phys));
+
   MapPage(cr3, addr, phys);
   return phys;
 }

zion/memory/physical_memory.cpp

@@ -8,6 +8,17 @@
 namespace phys_mem {
 namespace {
 
+uint64_t* PageAlign(uint64_t* addr) {
+  return reinterpret_cast<uint64_t*>(reinterpret_cast<uint64_t>(addr) & ~0xFFF);
+}
+
+void ZeroOutPage(uint64_t* ptr) {
+  ptr = PageAlign(ptr);
+  for (uint64_t i = 0; i < 512; i++) {
+    ptr[i] = 0;
+  }
+}
+
 struct BootstrapMemory {
   uint64_t init_page = 0;
   uint64_t next_page = 0;
@@ -163,6 +174,13 @@ uint64_t AllocatePage() {
   return page;
 }
 
+uint64_t AllocateAndZeroPage() {
+  uint64_t paddr = AllocatePage();
+  ZeroOutPage(
+      reinterpret_cast<uint64_t*>(boot::GetHigherHalfDirectMap() + paddr));
+  return paddr;
+}
+
 uint64_t AllocateContinuous(uint64_t num_continuous) {
   if (gPmm == nullptr) {
     panic("No physical memory manager!");

zion/memory/physical_memory.h

@@ -10,9 +10,12 @@ namespace phys_mem {
 // to initialize so we need this first.
 void InitBootstrapPageAllocation();
 
+// Initializes the main physical memory manager.
 void InitPhysicalMemoryManager();
 
 uint64_t AllocatePage();
+uint64_t AllocateAndZeroPage();
+
 uint64_t AllocateContinuous(uint64_t num_pages);
 void FreePage(uint64_t page);