s390/boot: avoid mapping standby memory

Commit bb1520d5 ("s390/mm: start kernel with DAT enabled")
doesn't consider online memory holes due to potential memory offlining
and erroneously creates pgtables for stand-by memory, which bear RW+X
attribute and trigger a warning:

RANGE                                 SIZE   STATE REMOVABLE BLOCK
0x0000000000000000-0x0000000c3fffffff  49G  online       yes  0-48
0x0000000c40000000-0x0000000c7fffffff   1G offline              49
0x0000000c80000000-0x0000000fffffffff  14G  online       yes 50-63
0x0000001000000000-0x00000013ffffffff  16G offline           64-79

    s390/mm: Found insecure W+X mapping at address 0xc40000000
    WARNING: CPU: 14 PID: 1 at arch/s390/mm/dump_pagetables.c:142 note_page+0x2cc/0x2d8

Map only online memory ranges which fit within identity mapping limit.

Fixes: bb1520d5 ("s390/mm: start kernel with DAT enabled")
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/boot/boot.h

@@ -44,7 +44,7 @@ void print_missing_facilities(void);
 void sclp_early_setup_buffer(void);
 void print_pgm_check_info(void);
 unsigned long get_random_base(unsigned long safe_addr);
-void setup_vmem(unsigned long online_end, unsigned long asce_limit);
+void setup_vmem(unsigned long ident_map_size, unsigned long asce_limit);
 void __printf(1, 2) decompressor_printk(const char *fmt, ...);
 void error(char *m);
 

arch/s390/boot/startup.c

@@ -278,7 +278,6 @@ void startup_kernel(void)
 	unsigned long random_lma;
 	unsigned long safe_addr;
 	unsigned long asce_limit;
-	unsigned long online_end;
 	void *img;
 	psw_t psw;
 
@@ -303,7 +302,6 @@ void startup_kernel(void)
 	setup_ident_map_size(detect_memory());
 	setup_vmalloc_size();
 	asce_limit = setup_kernel_memory_layout();
-	online_end = min(get_mem_detect_end(), ident_map_size);
 
 	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE) && kaslr_enabled) {
 		random_lma = get_random_base(safe_addr);
@@ -335,7 +333,7 @@ void startup_kernel(void)
 	 */
 	clear_bss_section();
 	handle_relocs(__kaslr_offset);
-	setup_vmem(online_end, asce_limit);
+	setup_vmem(ident_map_size, asce_limit);
 	copy_bootdata();
 
 	if (__kaslr_offset) {

arch/s390/boot/vmem.c

@@ -39,7 +39,7 @@ static void boot_check_oom(void)
 		error("out of memory on boot\n");
 }
 
-static void pgtable_populate_begin(unsigned long online_end)
+static void pgtable_populate_begin(unsigned long ident_map_size)
 {
 	unsigned long initrd_end;
 	unsigned long kernel_end;
@@ -51,7 +51,7 @@ static void pgtable_populate_begin(unsigned long online_end)
 		pgalloc_low = max(pgalloc_low, initrd_end);
 	}
 
-	pgalloc_end = round_down(online_end, PAGE_SIZE);
+	pgalloc_end = round_down(min(ident_map_size, get_mem_detect_end()), PAGE_SIZE);
 	pgalloc_pos = pgalloc_end;
 
 	boot_check_oom();
@@ -247,10 +247,12 @@ static void pgtable_populate_end(void)
 	} while (pgalloc_pos < pgalloc_pos_prev);
 }
 
-void setup_vmem(unsigned long online_end, unsigned long asce_limit)
+void setup_vmem(unsigned long ident_map_size, unsigned long asce_limit)
 {
+	unsigned long start, end;
 	unsigned long asce_type;
 	unsigned long asce_bits;
+	int i;
 
 	if (asce_limit == _REGION1_SIZE) {
 		asce_type = _REGION2_ENTRY_EMPTY;
@@ -272,9 +274,13 @@ void setup_vmem(unsigned long online_end, unsigned long asce_limit)
 	 * No further pgtable_populate() calls are allowed after the value
 	 * of pgalloc_pos finalized with a call to pgtable_populate_end().
 	 */
-	pgtable_populate_begin(online_end);
+	pgtable_populate_begin(ident_map_size);
 	pgtable_populate(0, sizeof(struct lowcore), POPULATE_ONE2ONE);
-	pgtable_populate(0, online_end, POPULATE_ONE2ONE);
+	for_each_mem_detect_block(i, &start, &end) {
+		if (start >= ident_map_size)
+			break;
+		pgtable_populate(start, min(end, ident_map_size), POPULATE_ONE2ONE);
+	}
 	pgtable_populate(__abs_lowcore, __abs_lowcore + sizeof(struct lowcore),
 			 POPULATE_ABS_LOWCORE);
 	pgtable_populate(__memcpy_real_area, __memcpy_real_area + PAGE_SIZE,