Re: [PATCH v2 11/11] dm crypt: Fix zoned block device support

[Hannes Reinecke <hare@suse.de>]

On 5/20/21 6:22 AM, Damien Le Moal wrote:
> Zone append BIOs (REQ_OP_ZONE_APPEND) always specify the start sector
> of the zone to be written instead of the actual sector location to
> write. The write location is determined by the device and returned to
> the host upon completion of the operation. This interface, while simple
> and efficient for writing into sequential zones of a zoned block
> device, is incompatible with the use of sector values to calculate a
> cypher block IV. All data written in a zone end up using the same IV
> values corresponding to the first sectors of the zone, but read
> operation will specify any sector within the zone resulting in an IV
> mismatch between encryption and decryption.
> 
> To solve this problem, report to DM core that zone append operations are
> not supported. This result in the zone append operations being emulated
> using regular write operations.
> 
> Reported-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
> ---
>   drivers/md/dm-crypt.c | 24 +++++++++++++++++++-----
>   1 file changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
> index f410ceee51d7..50f4cbd600d5 100644
> --- a/drivers/md/dm-crypt.c
> +++ b/drivers/md/dm-crypt.c
> @@ -3280,14 +3280,28 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
>   	}
>   	cc->start = tmpll;
>   
> -	/*
> -	 * For zoned block devices, we need to preserve the issuer write
> -	 * ordering. To do so, disable write workqueues and force inline
> -	 * encryption completion.
> -	 */
>   	if (bdev_is_zoned(cc->dev->bdev)) {
> +		/*
> +		 * For zoned block devices, we need to preserve the issuer write
> +		 * ordering. To do so, disable write workqueues and force inline
> +		 * encryption completion.
> +		 */
>   		set_bit(DM_CRYPT_NO_WRITE_WORKQUEUE, &cc->flags);
>   		set_bit(DM_CRYPT_WRITE_INLINE, &cc->flags);
> +
> +		/*
> +		 * All zone append writes to a zone of a zoned block device will
> +		 * have the same BIO sector, the start of the zone. When the
> +		 * cypher IV mode uses sector values, all data targeting a
> +		 * zone will be encrypted using the first sector numbers of the
> +		 * zone. This will not result in write errors but will
> +		 * cause most reads to fail as reads will use the sector values
> +		 * for the actual data locations, resulting in IV mismatch.
> +		 * To avoid this problem, ask DM core to emulate zone append
> +		 * operations with regular writes.
> +		 */
> +		DMDEBUG("Zone append operations will be emulated");
> +		ti->emulate_zone_append = true;
>   	}
>   
>   	if (crypt_integrity_aead(cc) || cc->integrity_iv_size) {
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
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