+/**\r
+ Initialize a buffer pool for page table use only.\r
+\r
+ To reduce the potential split operation on page table, the pages reserved for\r
+ page table should be allocated in the times of PAGE_TABLE_POOL_UNIT_PAGES and\r
+ at the boundary of PAGE_TABLE_POOL_ALIGNMENT. So the page pool is always\r
+ initialized with number of pages greater than or equal to the given PoolPages.\r
+\r
+ Once the pages in the pool are used up, this method should be called again to\r
+ reserve at least another PAGE_TABLE_POOL_UNIT_PAGES. Usually this won't happen\r
+ often in practice.\r
+\r
+ @param[in] PoolPages The least page number of the pool to be created.\r
+\r
+ @retval TRUE The pool is initialized successfully.\r
+ @retval FALSE The memory is out of resource.\r
+**/\r
+BOOLEAN\r
+InitializePageTablePool (\r
+ IN UINTN PoolPages\r
+ )\r
+{\r
+ VOID *Buffer;\r
+ BOOLEAN IsModified;\r
+\r
+ //\r
+ // Always reserve at least PAGE_TABLE_POOL_UNIT_PAGES, including one page for\r
+ // header.\r
+ //\r
+ PoolPages += 1; // Add one page for header.\r
+ PoolPages = ((PoolPages - 1) / PAGE_TABLE_POOL_UNIT_PAGES + 1) *\r
+ PAGE_TABLE_POOL_UNIT_PAGES;\r
+ Buffer = AllocateAlignedPages (PoolPages, PAGE_TABLE_POOL_ALIGNMENT);\r
+ if (Buffer == NULL) {\r
+ DEBUG ((DEBUG_ERROR, "ERROR: Out of aligned pages\r\n"));\r
+ return FALSE;\r
+ }\r
+\r
+ //\r
+ // Link all pools into a list for easier track later.\r
+ //\r
+ if (mPageTablePool == NULL) {\r
+ mPageTablePool = Buffer;\r
+ mPageTablePool->NextPool = mPageTablePool;\r
+ } else {\r
+ ((PAGE_TABLE_POOL *)Buffer)->NextPool = mPageTablePool->NextPool;\r
+ mPageTablePool->NextPool = Buffer;\r
+ mPageTablePool = Buffer;\r
+ }\r
+\r
+ //\r
+ // Reserve one page for pool header.\r
+ //\r
+ mPageTablePool->FreePages = PoolPages - 1;\r
+ mPageTablePool->Offset = EFI_PAGES_TO_SIZE (1);\r
+\r
+ //\r
+ // Mark the whole pool pages as read-only.\r
+ //\r
+ ConvertMemoryPageAttributes (\r
+ NULL,\r
+ (PHYSICAL_ADDRESS)(UINTN)Buffer,\r
+ EFI_PAGES_TO_SIZE (PoolPages),\r
+ EFI_MEMORY_RO,\r
+ PageActionSet,\r
+ AllocatePageTableMemory,\r
+ NULL,\r
+ &IsModified\r
+ );\r
+ ASSERT (IsModified == TRUE);\r
+\r
+ return TRUE;\r
+}\r
+\r
+/**\r
+ This API provides a way to allocate memory for page table.\r
+\r
+ This API can be called more than once to allocate memory for page tables.\r
+\r
+ Allocates the number of 4KB pages and returns a pointer to the allocated\r
+ buffer. The buffer returned is aligned on a 4KB boundary.\r
+\r
+ If Pages is 0, then NULL is returned.\r
+ If there is not enough memory remaining to satisfy the request, then NULL is\r
+ returned.\r
+\r
+ @param Pages The number of 4 KB pages to allocate.\r
+\r
+ @return A pointer to the allocated buffer or NULL if allocation fails.\r
+\r
+**/\r
+VOID *\r
+EFIAPI\r
+AllocatePageTableMemory (\r
+ IN UINTN Pages\r
+ )\r
+{\r
+ VOID *Buffer;\r
+\r
+ if (Pages == 0) {\r
+ return NULL;\r
+ }\r
+\r
+ //\r
+ // Renew the pool if necessary.\r
+ //\r
+ if (mPageTablePool == NULL ||\r
+ Pages > mPageTablePool->FreePages) {\r
+ if (!InitializePageTablePool (Pages)) {\r
+ return NULL;\r
+ }\r
+ }\r
+\r
+ Buffer = (UINT8 *)mPageTablePool + mPageTablePool->Offset;\r
+\r
+ mPageTablePool->Offset += EFI_PAGES_TO_SIZE (Pages);\r
+ mPageTablePool->FreePages -= Pages;\r
+\r
+ return Buffer;\r
+}\r
+\r