Re: [PATCH v2 10/20] s390/zcrypt/pkey: Rework cca findcard() implementation and callers

[Holger Dengler <dengler@linux.ibm.com>]

On 04/03/2025 18:21, Harald Freudenberger wrote:
> Rework the memory usage of the cca findcard() implementation:
> - findcard does not allocate memory for the list of apqns
>   any more.
> - the callers are now responsible to provide an array of
>   apqns to store the matching apqns into.
> 
> Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>

See my comments below.

> ---
>  drivers/s390/crypto/pkey_cca.c       | 25 +++++++++++--------------
>  drivers/s390/crypto/zcrypt_ccamisc.c | 18 ++++--------------
>  drivers/s390/crypto/zcrypt_ccamisc.h | 12 +++++-------
>  3 files changed, 20 insertions(+), 35 deletions(-)
> 
[...]
> diff --git a/drivers/s390/crypto/zcrypt_ccamisc.c b/drivers/s390/crypto/zcrypt_ccamisc.c
> index 65b4cdb9b478..d3b093dcdf30 100644
> --- a/drivers/s390/crypto/zcrypt_ccamisc.c
> +++ b/drivers/s390/crypto/zcrypt_ccamisc.c
[...]
> @@ -2006,17 +1999,14 @@ int cca_findcard2(u32 **apqns, u32 *nr_apqns, u16 cardnr, u16 domain,
>  				continue;
>  		}
>  		/* apqn passed all filtering criterons, add to the array */
> -		if (_nr_apqns < 256)
> -			_apqns[_nr_apqns++] = (((u16)card) << 16) | ((u16)dom);
> +		if (_nr_apqns < *nr_apqns)
> +			apqns[_nr_apqns++] = (((u16)card) << 16) | ((u16)dom);
>  	}
>  
>  	/* nothing found ? */
>  	if (!_nr_apqns) {
> -		kfree(_apqns);
>  		rc = -ENODEV;

In my opinion, the -ENODEV return value can be completely dropped. For the caller it should be sufficient to check for nr_apqns == 0.

>  	} else {
> -		/* no re-allocation, simple return the _apqns array */
> -		*apqns = _apqns;
>  		*nr_apqns = _nr_apqns;

Please update *nr_apqns unconditionally.

>  		rc = 0;
>  	}
> diff --git a/drivers/s390/crypto/zcrypt_ccamisc.h b/drivers/s390/crypto/zcrypt_ccamisc.h
> index 273edf2bb036..bed647a42eb2 100644
> --- a/drivers/s390/crypto/zcrypt_ccamisc.h
> +++ b/drivers/s390/crypto/zcrypt_ccamisc.h
> @@ -229,14 +229,12 @@ int cca_findcard(const u8 *key, u16 *pcardnr, u16 *pdomain, int verify);
>   *   cur_mkvp or old_mkvp values of the apqn are used.
>   * The mktype determines which set of master keys to use:
>   *   0 = AES_MK_SET - AES MK set, 1 = APKA MK_SET - APKA MK set
> - * The array of apqn entries is allocated with kmalloc and returned in *apqns;
> - * the number of apqns stored into the list is returned in *nr_apqns. One apqn
> - * entry is simple a 32 bit value with 16 bit cardnr and 16 bit domain nr and
> - * may be casted to struct pkey_apqn. The return value is either 0 for success
> - * or a negative errno value. If no apqn meeting the criteria is found,
> - * -ENODEV is returned.
> + * The caller should set *nr_apqns to the nr of elements available in *apqns.
> + * On return *nr_apqns is then updated with the nr of apqns filled into *apqns.
> + * The return value is either 0 for success or a negative errno value.
> + * If no apqn meeting the criteria is found, -ENODEV is returned.

Why not just return nr_apqns == 0 to indicate, that no matching device has been found? Anyhow, even if you would stay with the -ENODEV return value, *nr_apqns should be updated in any case.

>   */
> -int cca_findcard2(u32 **apqns, u32 *nr_apqns, u16 cardnr, u16 domain,
> +int cca_findcard2(u32 *apqns, u32 *nr_apqns, u16 cardnr, u16 domain,
>  		  int minhwtype, int mktype, u64 cur_mkvp, u64 old_mkvp,
>  		  int verify);
>  

-- 
Mit freundlichen Grüßen / Kind regards
Holger Dengler
--
IBM Systems, Linux on IBM Z Development
dengler@linux.ibm.com