arm64:mm: free the useless initial page table

For 64K page system, after mapping a PMD section, the corresponding initial
page table is not needed any more. That page can be freed.

Signed-off-by: Zhichang Yuan <zhichang.yuan@linaro.org>
[catalin.marinas@arm.com: added BUG_ON() to catch late memblock freeing]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/pgtable.h

@@ -342,9 +342,12 @@ extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
 
 #ifdef CONFIG_ARM64_64K_PAGES
 #define pud_sect(pud)		(0)
+#define pud_table(pud)		(1)
 #else
 #define pud_sect(pud)		((pud_val(pud) & PUD_TYPE_MASK) == \
 				 PUD_TYPE_SECT)
+#define pud_table(pud)		((pud_val(pud) & PUD_TYPE_MASK) == \
+				 PUD_TYPE_TABLE)
 #endif
 
 static inline void set_pmd(pmd_t *pmdp, pmd_t pmd)

arch/arm64/mm/mmu.c

@@ -153,8 +153,14 @@ static void alloc_init_pmd(struct mm_struct *mm, pud_t *pud,
 			 * Check for previous table entries created during
 			 * boot (__create_page_tables) and flush them.
 			 */
-			if (!pmd_none(old_pmd))
+			if (!pmd_none(old_pmd)) {
 				flush_tlb_all();
+				if (pmd_table(old_pmd)) {
+					phys_addr_t table = __pa(pte_offset_map(&old_pmd, 0));
+					BUG_ON(alloc != early_alloc);
+					memblock_free(table, PAGE_SIZE);
+				}
+			}
 		} else {
 			alloc_init_pte(pmd, addr, next, __phys_to_pfn(phys),
 				       prot, alloc);
@@ -209,9 +215,12 @@ static void alloc_init_pud(struct mm_struct *mm, pgd_t *pgd,
 			 * Look up the old pmd table and free it.
 			 */
 			if (!pud_none(old_pud)) {
-				phys_addr_t table = __pa(pmd_offset(&old_pud, 0));
-				memblock_free(table, PAGE_SIZE);
 				flush_tlb_all();
+				if (pud_table(old_pud)) {
+					phys_addr_t table = __pa(pmd_offset(&old_pud, 0));
+					BUG_ON(alloc != early_alloc);
+					memblock_free(table, PAGE_SIZE);
+				}
 			}
 		} else {
 			alloc_init_pmd(mm, pud, addr, next, phys, prot, alloc);