scsi: scsi_debug: Disallow zone sizes that are not powers of 2

Allowing a non-power-of-2 zone size forces the use of direct division
operations of 64-bit sector values to obtain a zone number or number of
zones. Doing so without using do_div() leads to compilation errors on
32-bit architectures.

Devices with a zone size that is not a power of 2 do not exist today so
allowing their emulation is of limited interest as the sd driver will not
support them anyway. To fix this compilation error, instead of using
do_div() for sector values divisions, simply disallow zone size values that
are not a power of 2.

[mkp: commit desc]

Link: https://lore.kernel.org/r/20200507023526.221574-1-damien.lemoal@wdc.com
Fixes: 98e0a689 ("scsi: scsi_debug: Add zone_size_mb module parameter")
Fixes: f0d1cf93 ("scsi: scsi_debug: Add ZBC zone commands")
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_debug.c

@@ -2657,13 +2657,7 @@ static inline bool sdebug_dev_is_zoned(struct sdebug_dev_info *devip)
 static struct sdeb_zone_state *zbc_zone(struct sdebug_dev_info *devip,
 					unsigned long long lba)
 {
-	unsigned int zno;
-
-	if (devip->zsize_shift)
-		zno = lba >> devip->zsize_shift;
-	else
-		zno = lba / devip->zsize;
-	return &devip->zstate[zno];
+	return &devip->zstate[lba >> devip->zsize_shift];
 }
 
 static inline bool zbc_zone_is_conv(struct sdeb_zone_state *zsp)
@@ -4306,7 +4300,7 @@ static int resp_report_zones(struct scsi_cmnd *scp,
 		return check_condition_result;
 	}
 
-	max_zones = devip->nr_zones - zs_lba / devip->zsize;
+	max_zones = devip->nr_zones - (zs_lba >> devip->zsize_shift);
 	rep_max_zones = min((alloc_len - 64) >> ilog2(RZONES_DESC_HD),
 			    max_zones);
 
@@ -4826,6 +4820,10 @@ static int sdebug_device_create_zones(struct sdebug_dev_info *devip)
 			return -EINVAL;
 		}
 	} else {
+		if (!is_power_of_2(sdeb_zbc_zone_size_mb)) {
+			pr_err("Zone size is not a power of 2\n");
+			return -EINVAL;
+		}
 		devip->zsize = (sdeb_zbc_zone_size_mb * SZ_1M)
 			>> ilog2(sdebug_sector_size);
 		if (devip->zsize >= capacity) {
@@ -4834,7 +4832,6 @@ static int sdebug_device_create_zones(struct sdebug_dev_info *devip)
 		}
 	}
 
-	if (is_power_of_2(devip->zsize))
 	devip->zsize_shift = ilog2(devip->zsize);
 	devip->nr_zones = (capacity + devip->zsize - 1) >> devip->zsize_shift;