From dcc160b3a090b1ffa0710ed72ae325be37298c0e Mon Sep 17 00:00:00 2001 From: Harald Freudenberger Date: Thu, 24 Apr 2025 15:35:57 +0200 Subject: s390/ap: Introduce ap message buffer pool There is a need for a do-not-allocate-memory path through the AP bus layer. The pkey layer may be triggered via the in-kernel interface from a protected key crypto algorithm (namely PAES) to convert a secure key into a protected key. This happens in a workqueue context, so sleeping is allowed but memory allocations causing IO operations are not permitted. To accomplish this, an AP message memory pool with pre-allocated space is established. When ap_init_apmsg() with use_mempool set to true is called, instead of kmalloc() the ap message buffer is allocated from the ap_msg_pool. This pool only holds a limited amount of buffers: ap_msg_pool_min_items with the item size AP_DEFAULT_MAX_MSG_SIZE and exactly one of these items (if available) is returned if ap_init_apmsg() with the use_mempool arg set to true is called. When this pool is exhausted and use_mempool is set true, ap_init_apmsg() returns -ENOMEM without any attempt to allocate memory and the caller has to deal with that. Default values for this mempool of ap messages is: * Each buffer is 12KB (that is the default AP bus size and all the urgent messages should fit into this space). * Minimum items held in the pool is 8. This value is adjustable via module parameter ap.msgpool_min_items. The zcrypt layer may use this flag to indicate to the ap bus that the processing path for this message should not allocate memory but should use pre-allocated memory buffer instead. This is to prevent deadlocks with crypto and io for example with encrypted swap volumes. Signed-off-by: Harald Freudenberger Reviewed-by: Holger Dengler Link: https://lore.kernel.org/r/20250424133619.16495-4-freude@linux.ibm.com Signed-off-by: Heiko Carstens --- drivers/s390/crypto/ap_bus.c | 54 +++++++++++++++++++++++++++++++++++++--- drivers/s390/crypto/ap_bus.h | 3 ++- drivers/s390/crypto/zcrypt_api.c | 10 ++++---- 3 files changed, 58 insertions(+), 9 deletions(-) diff --git a/drivers/s390/crypto/ap_bus.c b/drivers/s390/crypto/ap_bus.c index 8935b3ee3a33..1e4784e9efd1 100644 --- a/drivers/s390/crypto/ap_bus.c +++ b/drivers/s390/crypto/ap_bus.c @@ -41,6 +41,7 @@ #include #include #include +#include #include "ap_bus.h" #include "ap_debug.h" @@ -102,6 +103,27 @@ static struct ap_config_info *const ap_qci_info_old = &qci[1]; */ debug_info_t *ap_dbf_info; +/* + * There is a need for a do-not-allocate-memory path through the AP bus + * layer. The pkey layer may be triggered via the in-kernel interface from + * a protected key crypto algorithm (namely PAES) to convert a secure key + * into a protected key. This happens in a workqueue context, so sleeping + * is allowed but memory allocations causing IO operations are not permitted. + * To accomplish this, an AP message memory pool with pre-allocated space + * is established. When ap_init_apmsg() with use_mempool set to true is + * called, instead of kmalloc() the ap message buffer is allocated from + * the ap_msg_pool. This pool only holds a limited amount of buffers: + * ap_msg_pool_min_items with the item size AP_DEFAULT_MAX_MSG_SIZE and + * exactly one of these items (if available) is returned if ap_init_apmsg() + * with the use_mempool arg set to true is called. When this pool is exhausted + * and use_mempool is set true, ap_init_apmsg() returns -ENOMEM without + * any attempt to allocate memory and the caller has to deal with that. + */ +static mempool_t *ap_msg_pool; +static unsigned int ap_msg_pool_min_items = 8; +module_param_named(msgpool_min_items, ap_msg_pool_min_items, uint, 0440); +MODULE_PARM_DESC(msgpool_min_items, "AP message pool minimal items"); + /* * AP bus rescan related things. */ @@ -550,11 +572,22 @@ static void ap_poll_thread_stop(void) /* * ap_init_apmsg() - Initialize ap_message. */ -int ap_init_apmsg(struct ap_message *ap_msg) +int ap_init_apmsg(struct ap_message *ap_msg, bool use_mempool) { - unsigned int maxmsgsize = atomic_read(&ap_max_msg_size); + unsigned int maxmsgsize; memset(ap_msg, 0, sizeof(*ap_msg)); + + if (use_mempool) { + ap_msg->msg = mempool_alloc_preallocated(ap_msg_pool); + if (!ap_msg->msg) + return -ENOMEM; + ap_msg->bufsize = AP_DEFAULT_MAX_MSG_SIZE; + ap_msg->flags |= AP_MSG_FLAG_MEMPOOL; + return 0; + } + + maxmsgsize = atomic_read(&ap_max_msg_size); ap_msg->msg = kmalloc(maxmsgsize, GFP_KERNEL); if (!ap_msg->msg) return -ENOMEM; @@ -569,7 +602,12 @@ EXPORT_SYMBOL(ap_init_apmsg); */ void ap_release_apmsg(struct ap_message *ap_msg) { - kfree_sensitive(ap_msg->msg); + if (ap_msg->flags & AP_MSG_FLAG_MEMPOOL) { + memzero_explicit(ap_msg->msg, ap_msg->bufsize); + mempool_free(ap_msg->msg, ap_msg_pool); + } else { + kfree_sensitive(ap_msg->msg); + } } EXPORT_SYMBOL(ap_release_apmsg); @@ -2457,6 +2495,14 @@ static int __init ap_module_init(void) /* init ap_queue hashtable */ hash_init(ap_queues); + /* create ap msg buffer memory pool */ + ap_msg_pool = mempool_create_kmalloc_pool(ap_msg_pool_min_items, + AP_DEFAULT_MAX_MSG_SIZE); + if (!ap_msg_pool) { + rc = -ENOMEM; + goto out; + } + /* set up the AP permissions (ioctls, ap and aq masks) */ ap_perms_init(); @@ -2503,6 +2549,7 @@ out_device: out_bus: bus_unregister(&ap_bus_type); out: + mempool_destroy(ap_msg_pool); ap_debug_exit(); return rc; } @@ -2513,6 +2560,7 @@ static void __exit ap_module_exit(void) ap_irq_exit(); root_device_unregister(ap_root_device); bus_unregister(&ap_bus_type); + mempool_destroy(ap_msg_pool); ap_debug_exit(); } diff --git a/drivers/s390/crypto/ap_bus.h b/drivers/s390/crypto/ap_bus.h index 483231bcdea6..60c41d8116ad 100644 --- a/drivers/s390/crypto/ap_bus.h +++ b/drivers/s390/crypto/ap_bus.h @@ -236,8 +236,9 @@ struct ap_message { #define AP_MSG_FLAG_SPECIAL 0x0001 /* flag msg as 'special' with NQAP */ #define AP_MSG_FLAG_USAGE 0x0002 /* CCA, EP11: usage (no admin) msg */ #define AP_MSG_FLAG_ADMIN 0x0004 /* CCA, EP11: admin (=control) msg */ +#define AP_MSG_FLAG_MEMPOOL 0x0008 /* ap msg buffer allocated via mempool */ -int ap_init_apmsg(struct ap_message *ap_msg); +int ap_init_apmsg(struct ap_message *ap_msg, bool use_mempool); void ap_release_apmsg(struct ap_message *ap_msg); enum ap_sm_wait ap_sm_event(struct ap_queue *aq, enum ap_sm_event event); diff --git a/drivers/s390/crypto/zcrypt_api.c b/drivers/s390/crypto/zcrypt_api.c index 8c263a9b643d..139bf2b13544 100644 --- a/drivers/s390/crypto/zcrypt_api.c +++ b/drivers/s390/crypto/zcrypt_api.c @@ -648,7 +648,7 @@ static long zcrypt_rsa_modexpo(struct ap_perms *perms, trace_s390_zcrypt_req(mex, TP_ICARSAMODEXPO); - rc = ap_init_apmsg(&ap_msg); + rc = ap_init_apmsg(&ap_msg, false); if (rc) goto out; @@ -753,7 +753,7 @@ static long zcrypt_rsa_crt(struct ap_perms *perms, trace_s390_zcrypt_req(crt, TP_ICARSACRT); - rc = ap_init_apmsg(&ap_msg); + rc = ap_init_apmsg(&ap_msg, false); if (rc) goto out; @@ -861,7 +861,7 @@ static long _zcrypt_send_cprb(bool userspace, struct ap_perms *perms, xcrb->status = 0; - rc = ap_init_apmsg(&ap_msg); + rc = ap_init_apmsg(&ap_msg, false); if (rc) goto out; @@ -1045,7 +1045,7 @@ 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); + rc = ap_init_apmsg(&ap_msg, false); if (rc) goto out; @@ -1219,7 +1219,7 @@ static long zcrypt_rng(char *buffer) trace_s390_zcrypt_req(buffer, TP_HWRNGCPRB); - rc = ap_init_apmsg(&ap_msg); + rc = ap_init_apmsg(&ap_msg, false); if (rc) goto out; rc = prep_rng_ap_msg(&ap_msg, &func_code, &domain); -- cgit v1.2.3