s390/kasan: remove identity mapping support

The identity mapping is created in the decompressor,
there is no need to have the same functionality in
the kasan setup code. Thus, remove it.

Remove the 4KB pages check for first 1MB since there
is no need to take care of the lowcore pages.

Acked-by: Heiko Carstens <[e-mail]>
Signed-off-by: Alexander Gordeev <[e-mail]>
Signed-off-by: Heiko Carstens <[e-mail]>

arch/s390/mm/kasan_init.c

···
 }
 
 enum populate_mode {
-	POPULATE_ONE2ONE,
 	POPULATE_MAP,
 	POPULATE_ZERO_SHADOW,
 	POPULATE_SHALLOW
···
 	pmd_t pmd;
 	pte_t pte;
 
-	if (!has_nx)
+	if (!has_nx) {
 		pgt_prot_zero = pgprot_clear_bit(pgt_prot_zero, _PAGE_NOEXEC);
-	if (!has_nx || mode == POPULATE_ONE2ONE) {
 		pgt_prot = pgprot_clear_bit(pgt_prot, _PAGE_NOEXEC);
 		sgt_prot = pgprot_clear_bit(sgt_prot, _SEGMENT_ENTRY_NOEXEC);
 	}
 
-	/*
-	 * The first 1MB of 1:1 mapping is mapped with 4KB pages
-	 */
 	while (address < end) {
 		pg_dir = pgd_offset_k(address);
 		if (pgd_none(*pg_dir)) {
···
 					pmd_populate(&init_mm, pm_dir, kasan_early_shadow_pte);
 					address = (address + PMD_SIZE) & PMD_MASK;
 					continue;
-				} else if (has_edat && address) {
-					void *page;
+				} else if (has_edat) {
+					void *page = kasan_early_alloc_segment();
 
-					if (mode == POPULATE_ONE2ONE) {
-						page = (void *)address;
-					} else {
-						page = kasan_early_alloc_segment();
-						memset(page, 0, _SEGMENT_SIZE);
-					}
+					memset(page, 0, _SEGMENT_SIZE);
 					pmd = __pmd(__pa(page));
 					pmd = set_pmd_bit(pmd, sgt_prot);
 					set_pmd(pm_dir, pmd);
···
 			void *page;
 
 			switch (mode) {
-			case POPULATE_ONE2ONE:
-				page = (void *)address;
-				pte = __pte(__pa(page));
-				pte = set_pte_bit(pte, pgt_prot);
-				set_pte(pt_dir, pte);
-				break;
 			case POPULATE_MAP:
 				page = kasan_early_alloc_pages(0);
 				memset(page, 0, PAGE_SIZE);
···
 	 * - ident_map_size represents online + standby and memory limits
 	 *   accounted.
 	 * Kasan maps "memsize" right away.
-	 * [0, memsize]			- as identity mapping
 	 * [__sha(0), __sha(memsize)]	- shadow memory for identity mapping
 	 * The rest [memsize, ident_map_size] if memsize < ident_map_size
 	 * could be mapped/unmapped dynamically later during memory hotplug.