Kernel: Convert MemoryManager::allocate_user_physical_page to ErrorOr

This allows is to use the TRY macro at the call sites, instead of using
clunky null checks.

Kernel/Graphics/VirtIOGPU/FramebufferDevice.cpp

@@ -175,7 +175,7 @@ ErrorOr<void> FramebufferDevice::create_framebuffer()
     m_buffer_size = calculate_framebuffer_size(info.rect.width, info.rect.height);
     auto region_name = TRY(KString::formatted("VirtGPU FrameBuffer #{}", m_scanout.value()));
     m_framebuffer = TRY(MM.allocate_kernel_region(m_buffer_size * 2, region_name->view(), Memory::Region::Access::ReadWrite, AllocationStrategy::AllocateNow));
-    auto write_sink_page = MM.allocate_user_physical_page(Memory::MemoryManager::ShouldZeroFill::No).release_nonnull();
+    auto write_sink_page = TRY(MM.allocate_user_physical_page(Memory::MemoryManager::ShouldZeroFill::No));
     auto num_needed_pages = m_framebuffer->vmobject().page_count();
 
     NonnullRefPtrVector<Memory::PhysicalPage> pages;

Kernel/Memory/AnonymousVMObject.cpp

@@ -322,11 +322,12 @@ PageFaultResponse AnonymousVMObject::handle_cow_fault(size_t page_index, Virtual
         page = m_shared_committed_cow_pages->take_one();
     } else {
         dbgln_if(PAGE_FAULT_DEBUG, "    >> It's a COW page and it's time to COW!");
-        page = MM.allocate_user_physical_page(MemoryManager::ShouldZeroFill::No);
+        auto page_or_error = MM.allocate_user_physical_page(MemoryManager::ShouldZeroFill::No);
-        if (page.is_null()) {
+        if (page_or_error.is_error()) {
             dmesgln("MM: handle_cow_fault was unable to allocate a physical page");
             return PageFaultResponse::OutOfMemory;
         }
+        page = page_or_error.release_value();
     }
 
     dbgln_if(PAGE_FAULT_DEBUG, "      >> COW {} <- {}", page->paddr(), page_slot->paddr());

Kernel/Memory/MemoryManager.cpp

@@ -572,11 +572,12 @@ PageTableEntry* MemoryManager::ensure_pte(PageDirectory& page_directory, Virtual
         return &quickmap_pt(PhysicalAddress(pde.page_table_base()))[page_table_index];
 
     bool did_purge = false;
-    auto page_table = allocate_user_physical_page(ShouldZeroFill::Yes, &did_purge);
+    auto page_table_or_error = allocate_user_physical_page(ShouldZeroFill::Yes, &did_purge);
-    if (!page_table) {
+    if (page_table_or_error.is_error()) {
         dbgln("MM: Unable to allocate page table to map {}", vaddr);
         return nullptr;
     }
+    auto page_table = page_table_or_error.release_value();
     if (did_purge) {
         // If any memory had to be purged, ensure_pte may have been called as part
         // of the purging process. So we need to re-map the pd in this case to ensure
@@ -892,7 +893,7 @@ NonnullRefPtr<PhysicalPage> MemoryManager::allocate_committed_user_physical_page
     return page.release_nonnull();
 }
 
-RefPtr<PhysicalPage> MemoryManager::allocate_user_physical_page(ShouldZeroFill should_zero_fill, bool* did_purge)
+ErrorOr<NonnullRefPtr<PhysicalPage>> MemoryManager::allocate_user_physical_page(ShouldZeroFill should_zero_fill, bool* did_purge)
 {
     SpinlockLocker lock(s_mm_lock);
     auto page = find_free_user_physical_page(false);
@@ -918,7 +919,7 @@ RefPtr<PhysicalPage> MemoryManager::allocate_user_physical_page(ShouldZeroFill s
         });
         if (!page) {
             dmesgln("MM: no user physical pages available");
-            return {};
+            return ENOMEM;
         }
     }
 
@@ -930,7 +931,7 @@ RefPtr<PhysicalPage> MemoryManager::allocate_user_physical_page(ShouldZeroFill s
 
     if (did_purge)
         *did_purge = purged_pages;
-    return page;
+    return page.release_nonnull();
 }
 
 ErrorOr<NonnullRefPtrVector<PhysicalPage>> MemoryManager::allocate_contiguous_supervisor_physical_pages(size_t size)

Kernel/Memory/MemoryManager.h

@@ -171,7 +171,7 @@ public:
     void uncommit_user_physical_pages(Badge<CommittedPhysicalPageSet>, size_t page_count);
 
     NonnullRefPtr<PhysicalPage> allocate_committed_user_physical_page(Badge<CommittedPhysicalPageSet>, ShouldZeroFill = ShouldZeroFill::Yes);
-    RefPtr<PhysicalPage> allocate_user_physical_page(ShouldZeroFill = ShouldZeroFill::Yes, bool* did_purge = nullptr);
+    ErrorOr<NonnullRefPtr<PhysicalPage>> allocate_user_physical_page(ShouldZeroFill = ShouldZeroFill::Yes, bool* did_purge = nullptr);
     ErrorOr<NonnullRefPtr<PhysicalPage>> allocate_supervisor_physical_page();
     ErrorOr<NonnullRefPtrVector<PhysicalPage>> allocate_contiguous_supervisor_physical_pages(size_t size);
     void deallocate_physical_page(PhysicalAddress);

Kernel/Memory/PageDirectory.cpp

@@ -61,19 +61,13 @@ ErrorOr<NonnullRefPtr<PageDirectory>> PageDirectory::try_create_for_userspace(Vi
     SpinlockLocker lock(s_mm_lock);
 
 #if ARCH(X86_64)
-    directory->m_pml4t = MM.allocate_user_physical_page();
+    directory->m_pml4t = TRY(MM.allocate_user_physical_page());
-    if (!directory->m_pml4t)
-        return ENOMEM;
 #endif
 
-    directory->m_directory_table = MM.allocate_user_physical_page();
+    directory->m_directory_table = TRY(MM.allocate_user_physical_page());
-    if (!directory->m_directory_table)
-        return ENOMEM;
     auto kernel_pd_index = (kernel_mapping_base >> 30) & 0x1ffu;
     for (size_t i = 0; i < kernel_pd_index; i++) {
-        directory->m_directory_pages[i] = MM.allocate_user_physical_page();
+        directory->m_directory_pages[i] = TRY(MM.allocate_user_physical_page());
-        if (!directory->m_directory_pages[i])
-            return ENOMEM;
     }
 
     // Share the top 1 GiB of kernel-only mappings (>=kernel_mapping_base)

Kernel/Memory/Region.cpp

@@ -407,11 +407,12 @@ PageFaultResponse Region::handle_zero_fault(size_t page_index_in_region)
         page_slot = static_cast<AnonymousVMObject&>(*m_vmobject).allocate_committed_page({});
         dbgln_if(PAGE_FAULT_DEBUG, "      >> ALLOCATED COMMITTED {}", page_slot->paddr());
     } else {
-        page_slot = MM.allocate_user_physical_page(MemoryManager::ShouldZeroFill::Yes);
+        auto page_or_error = MM.allocate_user_physical_page(MemoryManager::ShouldZeroFill::Yes);
-        if (page_slot.is_null()) {
+        if (page_or_error.is_error()) {
             dmesgln("MM: handle_zero_fault was unable to allocate a physical page");
             return PageFaultResponse::OutOfMemory;
         }
+        page_slot = page_or_error.release_value();
         dbgln_if(PAGE_FAULT_DEBUG, "      >> ALLOCATED {}", page_slot->paddr());
     }
 
@@ -495,12 +496,12 @@ PageFaultResponse Region::handle_inode_fault(size_t page_index_in_region)
         return PageFaultResponse::Continue;
     }
 
-    vmobject_physical_page_entry = MM.allocate_user_physical_page(MemoryManager::ShouldZeroFill::No);
+    auto vmobject_physical_page_or_error = MM.allocate_user_physical_page(MemoryManager::ShouldZeroFill::No);
-
+    if (vmobject_physical_page_or_error.is_error()) {
-    if (vmobject_physical_page_entry.is_null()) {
         dmesgln("MM: handle_inode_fault was unable to allocate a physical page");
         return PageFaultResponse::OutOfMemory;
     }
+    vmobject_physical_page_entry = vmobject_physical_page_or_error.release_value();
 
     {
         SpinlockLocker mm_locker(s_mm_lock);