x86/mm/64: Make SPARSEMEM_VMEMMAP the only memory model

5-level paging only supports SPARSEMEM_VMEMMAP. CONFIG_X86_5LEVEL is
being phased out, making 5-level paging support mandatory.

Make CONFIG_SPARSEMEM_VMEMMAP mandatory for x86-64 and eliminate
any associated conditional statements.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250516123306.3812286-3-kirill.shutemov@linux.intel.com

Author: kiryl

arch/x86/Kconfig

@@ -1467,7 +1467,6 @@ config X86_PAE
 config X86_5LEVEL
 	bool "Enable 5-level page tables support"
 	default y
-	select SPARSEMEM_VMEMMAP
 	depends on X86_64
 	help
 	  5-level paging enables access to larger address space:
@@ -1579,6 +1578,7 @@ config ARCH_SPARSEMEM_ENABLE
 	def_bool y
 	select SPARSEMEM_STATIC if X86_32
 	select SPARSEMEM_VMEMMAP_ENABLE if X86_64
+	select SPARSEMEM_VMEMMAP if X86_64
 
 config ARCH_SPARSEMEM_DEFAULT
 	def_bool X86_64 || (NUMA && X86_32)

arch/x86/mm/init_64.c

@@ -833,7 +833,6 @@ void __init paging_init(void)
 	zone_sizes_init();
 }
 
-#ifdef CONFIG_SPARSEMEM_VMEMMAP
 #define PAGE_UNUSED 0xFD
 
 /*
@@ -932,7 +931,6 @@ static void __meminit vmemmap_use_new_sub_pmd(unsigned long start, unsigned long
 	if (!IS_ALIGNED(end, PMD_SIZE))
 		unused_pmd_start = end;
 }
-#endif
 
 /*
  * Memory hotplug specific functions
@@ -1152,16 +1150,13 @@ remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end,
 				pmd_clear(pmd);
 				spin_unlock(&init_mm.page_table_lock);
 				pages++;
-			}
-#ifdef CONFIG_SPARSEMEM_VMEMMAP
-			else if (vmemmap_pmd_is_unused(addr, next)) {
+			} else if (vmemmap_pmd_is_unused(addr, next)) {
 					free_hugepage_table(pmd_page(*pmd),
 							    altmap);
 					spin_lock(&init_mm.page_table_lock);
 					pmd_clear(pmd);
 					spin_unlock(&init_mm.page_table_lock);
 			}
-#endif
 			continue;
 		}
 
@@ -1500,7 +1495,6 @@ unsigned long memory_block_size_bytes(void)
 	return memory_block_size_probed;
 }
 
-#ifdef CONFIG_SPARSEMEM_VMEMMAP
 /*
  * Initialise the sparsemem vmemmap using huge-pages at the PMD level.
  */
@@ -1647,4 +1641,3 @@ void __meminit vmemmap_populate_print_last(void)
 		node_start = 0;
 	}
 }
-#endif