[Zion] Introduce the Kernel VMM to centralize allocs.

zion/CMakeLists.txt

@@ -15,6 +15,7 @@ add_executable(zion
   loader/init_loader.cpp
   memory/kernel_heap.cpp
   memory/kernel_stack_manager.cpp
+  memory/kernel_vmm.cpp
   memory/paging_util.cpp
   memory/physical_memory.cpp
   memory/slab_allocator.cpp

zion/memory/kernel_vmm.cpp

@@ -0,0 +1,32 @@
+#include "memory/kernel_vmm.h"
+
+#include "debug/debug.h"
+#include "memory/paging_util.h"
+
+namespace {
+
+KernelVmm* gKernelVmm = nullptr;
+
+}
+KernelVmm::KernelVmm() {
+  if (gKernelVmm) {
+    panic("KernelVmm double init.");
+  }
+  gKernelVmm = this;
+}
+
+uint64_t KernelVmm::AcquireSlabHeapRegion(uint64_t slab_size_bytes) {
+  return gKernelVmm->AcquireSlabHeapRegionInternal(slab_size_bytes);
+}
+
+uint64_t KernelVmm::AcquireSlabHeapRegionInternal(uint64_t slab_size_bytes) {
+  uint64_t next_slab = next_slab_heap_page_;
+  if (next_slab >= kKernelBuddyHeapEnd) {
+    panic("Slab heap overrun");
+  }
+  next_slab_heap_page_ += slab_size_bytes;
+  // TODO: Consider handling this as a part of a page-fault handler
+  // rather than auto mapping all over the place.
+  EnsureResident(next_slab, slab_size_bytes);
+  return next_slab;
+}

zion/memory/kernel_vmm.h

@@ -0,0 +1,17 @@
+#pragma once
+
+#include <stdint.h>
+
+#include "memory/constants.h"
+
+class KernelVmm {
+ public:
+  KernelVmm();
+
+  static uint64_t AcquireSlabHeapRegion(uint64_t slab_size_bytes);
+
+ private:
+  uint64_t next_slab_heap_page_ = kKernelSlabHeapStart;
+
+  uint64_t AcquireSlabHeapRegionInternal(uint64_t slab_size_bytes);
+};

zion/memory/slab_allocator.cpp

@@ -2,25 +2,13 @@
 
 #include "debug/debug.h"
 #include "memory/constants.h"
+#include "memory/kernel_vmm.h"
 #include "memory/paging_util.h"
 
 namespace {
 
-// TODO: Store these in a kernel VMM.
 const uint64_t kSlabSize = 4 * KiB;
 const uint64_t kSlabMask = ~(kSlabSize - 1);
-uint64_t gNextSlab = kKernelSlabHeapStart;
-
-uint64_t NextSlab() {
-  // FIXME: Synchronization.
-  uint64_t next_slab = gNextSlab;
-  if (next_slab >= kKernelBuddyHeapEnd) {
-    panic("Slab heap overrun");
-  }
-  gNextSlab += kSlabSize;
-  EnsureResident(next_slab, 1);
-  return next_slab;
-}
 
 }  // namespace
 
@@ -91,8 +79,8 @@ glcr::ErrorOr<void*> SlabAllocator::Allocate() {
     return slab->Allocate();
   }
 
-  dbgln("Allocating new kernel slab size {}", elem_size_);
-  void* next_slab = (uint64_t*)NextSlab();
+  void* next_slab =
+      reinterpret_cast<void*>(KernelVmm::AcquireSlabHeapRegion(kSlabSize));
   slabs_.PushFront(glcr::AdoptPtr(new (next_slab) Slab(elem_size_)));
   return slabs_.PeekFront()->Allocate();
 }

zion/zion.cpp

@@ -10,6 +10,7 @@
 #include "loader/init_loader.h"
 #include "memory/kernel_heap.h"
 #include "memory/kernel_stack_manager.h"
+#include "memory/kernel_vmm.h"
 #include "memory/paging_util.h"
 #include "memory/physical_memory.h"
 #include "scheduler/process_manager.h"
@@ -23,6 +24,7 @@ extern "C" void zion() {
 
   early_dbgln("[boot] Init Physical Memory Manager.");
   phys_mem::InitBootstrapPageAllocation();
+  KernelVmm kvmm;
   KernelHeap heap;
   phys_mem::InitPhysicalMemoryManager();
   phys_mem::DumpRegions();