Re: [PATCH v3 04/21] s390/ap/zcrypt: New xflag parameter

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

On 27/03/2025 15:39, Harald Freudenberger wrote:
> Introduce a new flag parameter for the both cprb send functions
> zcrypt_send_cprb() and zcrypt_send_ep11_cprb(). This new
> xflags parameter ("execution flags") shall be used to provide
> execution hints and flags for this crypto request.
> 
> There are two flags implemented to be used with these functions:
> * ZCRYPT_XFLAG_USERSPACE - indicates to the lower layers that
>   all the ptrs address userspace. So when construction the ap msg
>   copy_from_user() is to be used. If this flag is NOT set, the ptrs
>   address kernel memory and thus memcpy() is to be used.
> * ZCRYPT_XFLAG_NOMEMALLOC - indicates that this task must not
>   allocate memory which may be allocated with io operations.
>   For the zcrypt layer this limits the number of EP11 targets
>   to 16 APQNs. But as this flag is passed down the stack, it
>   may induce further restrictions.
> 
> For the AP bus and zcrypt message layer this means:
> * The ZCRYPT_XFLAG_USERSPACE is mapped to the already existing
>   bool variable "userspace" which is propagated to the zcrypt
>   proto implementations.
> * The ZCRYPT_XFLAG_NOMEMALLOC results in setting the AP flag
>   AP_MSG_FLAG_MEMPOOL when the AP msg buffer is initialized.
> 
> Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
> ---
>  drivers/s390/crypto/ap_bus.c          |  6 +--
>  drivers/s390/crypto/ap_bus.h          |  2 +-
>  drivers/s390/crypto/zcrypt_api.c      | 76 +++++++++++++++------------
>  drivers/s390/crypto/zcrypt_api.h      | 11 +++-
>  drivers/s390/crypto/zcrypt_ccamisc.c  | 16 +++---
>  drivers/s390/crypto/zcrypt_ep11misc.c | 10 ++--
>  6 files changed, 69 insertions(+), 52 deletions(-)
> 
[...]
> diff --git a/drivers/s390/crypto/zcrypt_api.c b/drivers/s390/crypto/zcrypt_api.c
> index ad09c5306e28..01cb72fed828 100644
> --- a/drivers/s390/crypto/zcrypt_api.c
> +++ b/drivers/s390/crypto/zcrypt_api.c
[...]
> @@ -1045,36 +1048,40 @@ static long _zcrypt_send_ep11_cprb(bool userspace, struct ap_perms *perms,
>  
>  	trace_s390_zcrypt_req(xcrb, TP_ZSENDEP11CPRB);
>  
> -	rc = ap_init_apmsg(&ap_msg, false);
> +	rc = ap_init_apmsg(&ap_msg, xflags & ZCRYPT_XFLAG_NOMEMALLOC ?
> +			   AP_MSG_FLAG_MEMPOOL : 0);
>  	if (rc)
>  		goto out;
>  
>  	target_num = (unsigned short)xcrb->targets_num;
>  
>  	/* empty list indicates autoselect (all available targets) */
> -	targets = NULL;
> +	rc = -ENOMEM;
>  	if (target_num != 0) {
>  		struct ep11_target_dev __user *uptr;
>  
> -		targets = kcalloc(target_num, sizeof(*targets), GFP_KERNEL);
> -		if (!targets) {
> -			func_code = 0;
> -			rc = -ENOMEM;
> +		if (target_num <= ARRAY_SIZE(targetbuf)) {
> +			targets = targetbuf;
> +		} else if (xflags & ZCRYPT_XFLAG_NOMEMALLOC) {
>  			goto out;
> +		} else {
> +			targets = kcalloc(target_num,
> +					  sizeof(*targets), GFP_KERNEL);
> +			if (!targets)
> +				goto out;

As discussed, this alloc&copy is only required in userspace path. If zcrypt_send_ep11_cprb() is called from userspace, the targets pointer can be used directly.

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