Kernel: Clean up the page fault handling code a bit

Not using "else" after "return" unnests the code and makes it easier to
follow. Also use an enum for the two different page fault types.

Kernel/Arch/i386/CPU.h

@@ -303,9 +303,16 @@ class PageFault {
  {
  }
 
+ enum class Type {
+ PageNotPresent,
+ ProtectionViolation,
+ };
+
  VirtualAddress vaddr() const { return m_vaddr; }
  u16 code() const { return m_code; }
 
+ Type type() const { return (Type)(m_code & 1); }
+
  bool is_not_present() const { return (m_code & 1) == PageFaultFlags::NotPresent; }
  bool is_protection_violation() const { return (m_code & 1) == PageFaultFlags::ProtectionViolation; }
  bool is_read() const { return (m_code & 2) == PageFaultFlags::Read; }

Kernel/VM/MemoryManager.cpp

@@ -405,7 +405,7 @@ PageFaultResponse MemoryManager::handle_page_fault(const PageFault& fault)
  dbgprintf("MM: handle_page_fault(%w) at L%x\n", fault.code(), fault.vaddr().get());
 #endif
  ASSERT(fault.vaddr() != m_quickmap_addr);
- if (fault.is_not_present() && fault.vaddr().get() >= 0xc0000000) {
+ if (fault.type() == PageFault::Type::PageNotPresent && fault.vaddr().get() >= 0xc0000000) {
  u32 page_directory_index = (fault.vaddr().get() >> 22) & 0x3ff;
  auto& kernel_pde = kernel_page_directory().entries()[page_directory_index];
  if (kernel_pde.is_present()) {
@@ -422,34 +422,30 @@ PageFaultResponse MemoryManager::handle_page_fault(const PageFault& fault)
  return PageFaultResponse::ShouldCrash;
  }
  auto page_index_in_region = region->page_index_from_address(fault.vaddr());
- if (fault.is_not_present()) {
+ if (fault.type() == PageFault::Type::PageNotPresent) {
  if (region->vmo().inode()) {
 #ifdef PAGE_FAULT_DEBUG
  dbgprintf("NP(inode) fault in Region{%p}[%u]\n", region, page_index_in_region);
 #endif
  page_in_from_inode(*region, page_index_in_region);
  return PageFaultResponse::Continue;
- } else {
+ }
 #ifdef PAGE_FAULT_DEBUG
-  dbgprintf("NP(zero) fault in Region{%p}[%u]\n", region, page_index_in_region);
+ dbgprintf("NP(zero) fault in Region{%p}[%u]\n", region, page_index_in_region);
 #endif
-  zero_page(*region, page_index_in_region);
-  return PageFaultResponse::Continue;
-  }
- } else if (fault.is_protection_violation()) {
-  if (region->should_cow(page_index_in_region)) {
+ zero_page(*region, page_index_in_region);
+ return PageFaultResponse::Continue;
+ }
+ ASSERT(fault.type() == PageFault::Type::ProtectionViolation);
+ if (region->should_cow(page_index_in_region)) {
 #ifdef PAGE_FAULT_DEBUG
-  dbgprintf("PV(cow) fault in Region{%p}[%u]\n", region, page_index_in_region);
+ dbgprintf("PV(cow) fault in Region{%p}[%u]\n", region, page_index_in_region);
 #endif
- bool success = copy_on_write(*region, page_index_in_region);
- ASSERT(success);
- return PageFaultResponse::Continue;
- }
- kprintf("PV(error) fault in Region{%p}[%u] at L%x\n", region, page_index_in_region, fault.vaddr().get());
- } else {
- ASSERT_NOT_REACHED();
+ bool success = copy_on_write(*region, page_index_in_region);
+ ASSERT(success);
+ return PageFaultResponse::Continue;
  }
-
+ kprintf("PV(error) fault in Region{%p}[%u] at L%x\n", region, page_index_in_region, fault.vaddr().get());
  return PageFaultResponse::ShouldCrash;
 }