[PATCH v2 1/1] s390/ap: Fix MAPML computation

[PATCH v2 1/1] s390/ap: Fix MAPML computation

[Finn Callies]

When the TAPQ subfunction of PQAP returns a value between 0 and 3 in the
ml field, the Principles of Operation states that the Maximum AP Message
Length (MAPML) must be 12 KB.

The previous code incorrectly calculated smaller sizes for ml values 1-2:
- ml=1: 4 KB instead of 12 KB
- ml=2: 8 KB instead of 12 KB

While no current hardware reports ml=1 or ml=2, this fix ensures correct
behavior for specification compliance and future-proofing.

The fix ensures all ml values 0-3 correctly use the 12 KB default, with
only values 4+ using the formula ml * 4096.

Reviewed-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Finn Callies <fcallies@linux.ibm.com>
---
 drivers/s390/crypto/ap_card.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/s390/crypto/ap_card.c b/drivers/s390/crypto/ap_card.c
index e827fbeb76fb..c86397f4ddcd 100644
--- a/drivers/s390/crypto/ap_card.c
+++ b/drivers/s390/crypto/ap_card.c
@@ -241,7 +241,7 @@ struct ap_card *ap_card_create(int id, struct ap_tapq_hwinfo hwinfo,
 	ac->ap_dev.device_type = comp_type;
 	ac->hwinfo = hwinfo;
 	ac->id = id;
-	ac->maxmsgsize = hwinfo.ml > 0 ?
+	ac->maxmsgsize = hwinfo.ml > 3 ?
 		hwinfo.ml * AP_TAPQ_ML_FIELD_CHUNK_SIZE : AP_DEFAULT_MAX_MSG_SIZE;
 
 	return ac;
-- 
Finn Callies <fcallies@linux.ibm.com>
Linux on Z - crypto

Re: [PATCH v2 1/1] s390/ap: Fix MAPML computation

[sashiko-bot]

> When the TAPQ subfunction of PQAP returns a value between 0 and 3 in the
> ml field, the Principles of Operation states that the Maximum AP Message
> Length (MAPML) must be 12 KB.
> 
> The previous code incorrectly calculated smaller sizes for ml values 1-2:
> - ml=1: 4 KB instead of 12 KB
> - ml=2: 8 KB instead of 12 KB
> 
> While no current hardware reports ml=1 or ml=2, this fix ensures correct
> behavior for specification compliance and future-proofing.
> 
> The fix ensures all ml values 0-3 correctly use the 12 KB default, with
> only values 4+ using the formula ml * 4096.
> 
> Reviewed-by: Harald Freudenberger <freude@linux.ibm.com>
> Signed-off-by: Finn Callies <fcallies@linux.ibm.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260805092928.26932-1-fcallies@linux.ibm.com?part=1

Re: [PATCH v2 1/1] s390/ap: Fix MAPML computation

[Heiko Carstens]

On Wed, Aug 05, 2026 at 11:29:28AM +0200, Finn Callies wrote:
> When the TAPQ subfunction of PQAP returns a value between 0 and 3 in the
> ml field, the Principles of Operation states that the Maximum AP Message
> Length (MAPML) must be 12 KB.
> 
> The previous code incorrectly calculated smaller sizes for ml values 1-2:
> - ml=1: 4 KB instead of 12 KB
> - ml=2: 8 KB instead of 12 KB
> 
> While no current hardware reports ml=1 or ml=2, this fix ensures correct
> behavior for specification compliance and future-proofing.
> 
> The fix ensures all ml values 0-3 correctly use the 12 KB default, with
> only values 4+ using the formula ml * 4096.
> 
> Reviewed-by: Harald Freudenberger <freude@linux.ibm.com>
> Signed-off-by: Finn Callies <fcallies@linux.ibm.com>
> ---
>  drivers/s390/crypto/ap_card.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Acked-by: Heiko Carstens <hca@linux.ibm.com>

Re: [PATCH v2 1/1] s390/ap: Fix MAPML computation

[Vasily Gorbik]

On Wed, Aug 05, 2026 at 11:29:28AM +0200, Finn Callies wrote:
> When the TAPQ subfunction of PQAP returns a value between 0 and 3 in the
> ml field, the Principles of Operation states that the Maximum AP Message
> Length (MAPML) must be 12 KB.
> 
> The previous code incorrectly calculated smaller sizes for ml values 1-2:
> - ml=1: 4 KB instead of 12 KB
> - ml=2: 8 KB instead of 12 KB
> 
> While no current hardware reports ml=1 or ml=2, this fix ensures correct
> behavior for specification compliance and future-proofing.
> 
> The fix ensures all ml values 0-3 correctly use the 12 KB default, with
> only values 4+ using the formula ml * 4096.
> 
> Reviewed-by: Harald Freudenberger <freude@linux.ibm.com>
> Signed-off-by: Finn Callies <fcallies@linux.ibm.com>
> ---
>  drivers/s390/crypto/ap_card.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Applied, thank you!