[Zion] Introduce the Kernel VMM to centralize allocs.

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;
+}