Douglas,
On 2018/08/06 13:51, Douglas Gilbert wrote:
> Add bounds_check "rw" attribute to the sd driver. It controls whether
> each read/write operation submission does an "out of range" bounds check
> and a LBA/number_of_blocks alignment bounds check. The mainline kernel
> currently does both these checks. This patch changes that default
> to bounds_check=false, that is: the two checks are not done.
>
> SBC, SBC-2, SBC-3 and draft SBC-4 are require a device server (i.e. a
"are require" -> "require"
> SCSI disk) to fail any media command in which the LBA+number_of_blocks
> exceeds the capacity of the disk. So why should the sd driver also
> check it, given the block layer generated the request and knows the
> disk capacity and the disk itself also checks it?
What about SATA drives for non read/write commands when accessible max address
is set lower to a value lower then native max address ? Need to dig again in the
code and the specs, but I think to remember that Linux disk capacity is in that
case set to accessible max address, but some commands may address beyond that
value.
> The block layer does almost all its block handling in units of 512 byte
> blocks whereas SCSI disks may have other logical block sizes (e.g. 4096
> byte logical blocks). So when the block sizes are different it is
> possible that there is an alignment issue. But if that occurs, it
> would be a logic issue in the block layer. Note that the current
> mainline code does this check even when it is not needed (e.g. when
> the logical block size of the disk is 512 bytes).
Of note here is that there is a special case that is not being handled: ZBC
drives with 512B logical and 4K physical blocks will accept any 512B aligned
read commands (that is any read command), but will require 4K aligned write
commands for sequential write preferred zones (writes to conventional zones can
be 512B aligned). Since there is currently no differentiation between read and
write commands for the alignment check, much less based on the target zone type
of these commands, checks are incomplete for ZBC & ZAC disks in the generic
block layer. These checks could be added to SD though now that a bitmap is
attached to the device request queue to indicate if a zone is conventional or
sequential. For such test to be effective, sdkp->bounds_check would need to be
forced to 1 for host managed zoned disks.
>
> Signed-off-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
> ---
>
> Should a mechanism be added so this could set/cleared by:
> - a LLD for all disks it controls
> - kernel boot time parameter?
>
> drivers/scsi/sd.c | 55 +++++++++++++++++++++++++++++++++++++----------
> drivers/scsi/sd.h | 1 +
> 2 files changed, 45 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index d1d08f039bdd..b17b8c66881d 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -522,6 +522,32 @@ max_write_same_blocks_store(struct device *dev, struct device_attribute *attr,
> }
> static DEVICE_ATTR_RW(max_write_same_blocks);
>
> +static ssize_t
> +bounds_check_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> + struct scsi_disk *sdkp = to_scsi_disk(dev);
> +
> + return sprintf(buf, "%u\n", sdkp->bounds_check);
> +}
> +
> +static ssize_t
> +bounds_check_store(struct device *dev, struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + struct scsi_disk *sdkp = to_scsi_disk(dev);
> + int err, n;
> +
> + if (!capable(CAP_SYS_ADMIN))
> + return -EACCES;
> +
> + err = kstrtoint(buf, 10, &n);
> + if (!err)
> + sdkp->bounds_check = !!n;
> +
> + return err ? err : count;
> +}
> +static DEVICE_ATTR_RW(bounds_check);
> +
> static struct attribute *sd_disk_attrs[] = {
> &dev_attr_cache_type.attr,
> &dev_attr_FUA.attr,
> @@ -535,6 +561,7 @@ static struct attribute *sd_disk_attrs[] = {
> &dev_attr_zeroing_mode.attr,
> &dev_attr_max_write_same_blocks.attr,
> &dev_attr_max_medium_access_timeouts.attr,
> + &dev_attr_bounds_check.attr,
> NULL,
> };
> ATTRIBUTE_GROUPS(sd_disk);
> @@ -1088,7 +1115,6 @@ static int sd_setup_read_write_cmnd(struct scsi_cmnd *cmd)
> struct scsi_disk *sdkp = scsi_disk(rq->rq_disk);
> sector_t lba = sectors_to_logical(sdp, blk_rq_pos(rq));
> unsigned int nr_blocks = sectors_to_logical(sdp, blk_rq_sectors(rq));
> - unsigned int mask = logical_to_sectors(sdp, 1) - 1;
> unsigned char protect, fua;
> bool write = rq_data_dir(rq) == WRITE;
> bool dif, dix;
> @@ -1106,17 +1132,24 @@ static int sd_setup_read_write_cmnd(struct scsi_cmnd *cmd)
> goto out;
> }
>
> - if (unlikely(blk_rq_pos(rq) + blk_rq_sectors(rq)
> - > logical_to_sectors(sdp, sdkp->capacity))) {
> - scmd_printk(KERN_ERR, cmd, "access beyond end of device\n");
> - ret = BLKPREP_KILL;
> - goto out;
> - }
> + if (sdkp->bounds_check) {
> + unsigned int mask = logical_to_sectors(sdp, 1) - 1;
>
> - if (unlikely((blk_rq_pos(rq) & mask) || (blk_rq_sectors(rq) & mask))) {
> - scmd_printk(KERN_ERR, cmd, "request not aligned to the logical block size\n");
> - ret = BLKPREP_KILL;
> - goto out;
> + if (unlikely(blk_rq_pos(rq) + blk_rq_sectors(rq)
> + > logical_to_sectors(sdp, sdkp->capacity))) {
> + scmd_printk(KERN_ERR, cmd,
> + "access beyond end of device\n");
> + ret = BLKPREP_KILL;
> + goto out;
> + }
> +
> + if (unlikely((blk_rq_pos(rq) & mask) ||
> + (blk_rq_sectors(rq) & mask))) {
> + scmd_printk(KERN_ERR, cmd,
> + "request not aligned to logical block size\n");
> + ret = BLKPREP_KILL;
> + goto out;
> + }
> }
>
> /*
> diff --git a/drivers/scsi/sd.h b/drivers/scsi/sd.h
> index 392c7d078ae3..6f58d130fb75 100644
> --- a/drivers/scsi/sd.h
> +++ b/drivers/scsi/sd.h
> @@ -117,6 +117,7 @@ struct scsi_disk {
> unsigned urswrz : 1;
> unsigned security : 1;
> unsigned ignore_medium_access_errors : 1;
> + unsigned bounds_check : 1;
> };
> #define to_scsi_disk(obj) container_of(obj,struct scsi_disk,dev)
>
>
--
Damien Le Moal
Western Digital Research
