s390/zcrypt: improve zcrypt retry behavior

This patch reworks and improves the zcrypt retry behavior:
- The zcrypt_rescan_req counter has been removed. This
  counter variable has been increased on some transport
  errors and was used as a gatekeeper for AP bus rescans.
- Rework of the zcrypt_process_rescan() function to not
  use the above counter variable any more. Instead now
  always the ap_bus_force_rescan() function is called
  (as this has been improved with a previous patch).
- As the zcrpyt_process_rescan() function is called in
  all cprb send functions in case of the first attempt
  to send failed with ENODEV now before the next attempt
  to send an cprb is started.
- Introduce a define ZCRYPT_WAIT_BINDINGS_COMPLETE_MS
  for the amount of milliseconds to have the zcrypt API
  wait for AP bindings complete. This amount has been
  reduced to 30s (was 60s). Some playing around showed
  that 30s is a really fair limit.

The result of the above together with the patches to
improve the AP scan bus functions is that after the
first loop of cprb send retries when the result is a
ENODEV the AP bus scan is always triggered (synchronous).
If the AP bus scan detects changes in the configuration,
all the send functions now retry when the first attempt
was failing with ENODEV in the hope that now a suitable
device has appeared.

About concurrency: The ap_bus_force_rescan() uses a mutex
to ensure only one active AP bus scan is running. Another
caller of this function is blocked as long as the scan is
running but does not cause yet another scan. Instead the
result of the 'other' scan is used. This affects only tasks
which run into an initial ENODEV. Tasks with successful
delivery of cprbs will never invoke the bus scan and thus
never get blocked by the mutex.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Holger Dengler <dengler@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

3 files changed, 58 insertions, 80 deletions

diff --git a/drivers/s390/crypto/zcrypt_api.c b/drivers/s390/crypto/zcrypt_api.c
index 56efaa63841f..02c503f16bc2 100644
--- a/drivers/s390/crypto/zcrypt_api.c
+++ b/drivers/s390/crypto/zcrypt_api.c
@@ -60,10 +60,6 @@ DEFINE_SPINLOCK(zcrypt_list_lock);
 LIST_HEAD(zcrypt_card_list);
 
 static atomic_t zcrypt_open_count = ATOMIC_INIT(0);
-static atomic_t zcrypt_rescan_count = ATOMIC_INIT(0);
-
-atomic_t zcrypt_rescan_req = ATOMIC_INIT(0);
-EXPORT_SYMBOL(zcrypt_rescan_req);
 
 static LIST_HEAD(zcrypt_ops_list);
 
@@ -72,20 +68,15 @@ debug_info_t *zcrypt_dbf_info;
 
 /*
  * Process a rescan of the transport layer.
- *
- * Returns 1, if the rescan has been processed, otherwise 0.
+ * Runs a synchronous AP bus rescan.
+ * Returns true if something has changed (for example the
+ * bus scan has found and build up new devices) and it is
+ * worth to do a retry. Otherwise false is returned meaning
+ * no changes on the AP bus level.
  */
-static inline int zcrypt_process_rescan(void)
-{
-	if (atomic_read(&zcrypt_rescan_req)) {
-		atomic_set(&zcrypt_rescan_req, 0);
-		atomic_inc(&zcrypt_rescan_count);
-		ap_bus_force_rescan();
-		ZCRYPT_DBF_INFO("%s rescan count=%07d\n", __func__,
-				atomic_inc_return(&zcrypt_rescan_count));
-		return 1;
-	}
-	return 0;
+static inline bool zcrypt_process_rescan(void)
+{
+	return ap_bus_force_rescan();
 }
 
 void zcrypt_msgtype_register(struct zcrypt_ops *zops)
@@ -1481,16 +1472,13 @@ static int icarsamodexpo_ioctl(struct ap_perms *perms, unsigned long arg)
 
 	do {
 		rc = zcrypt_rsa_modexpo(perms, &tr, &mex);
-		if (rc == -EAGAIN)
-			tr.again_counter++;
-	} while (rc == -EAGAIN && tr.again_counter < TRACK_AGAIN_MAX);
-	/* on failure: retry once again after a requested rescan */
-	if ((rc == -ENODEV) && (zcrypt_process_rescan()))
+	} while (rc == -EAGAIN && ++tr.again_counter < TRACK_AGAIN_MAX);
+
+	/* on ENODEV failure: retry once again after a requested rescan */
+	if (rc == -ENODEV && zcrypt_process_rescan())
 		do {
 			rc = zcrypt_rsa_modexpo(perms, &tr, &mex);
-			if (rc == -EAGAIN)
-				tr.again_counter++;
-		} while (rc == -EAGAIN && tr.again_counter < TRACK_AGAIN_MAX);
+		} while (rc == -EAGAIN && ++tr.again_counter < TRACK_AGAIN_MAX);
 	if (rc == -EAGAIN && tr.again_counter >= TRACK_AGAIN_MAX)
 		rc = -EIO;
 	if (rc) {
@@ -1513,16 +1501,13 @@ static int icarsacrt_ioctl(struct ap_perms *perms, unsigned long arg)
 
 	do {
 		rc = zcrypt_rsa_crt(perms, &tr, &crt);
-		if (rc == -EAGAIN)
-			tr.again_counter++;
-	} while (rc == -EAGAIN && tr.again_counter < TRACK_AGAIN_MAX);
-	/* on failure: retry once again after a requested rescan */
-	if ((rc == -ENODEV) && (zcrypt_process_rescan()))
+	} while (rc == -EAGAIN && ++tr.again_counter < TRACK_AGAIN_MAX);
+
+	/* on ENODEV failure: retry once again after a requested rescan */
+	if (rc == -ENODEV && zcrypt_process_rescan())
 		do {
 			rc = zcrypt_rsa_crt(perms, &tr, &crt);
-			if (rc == -EAGAIN)
-				tr.again_counter++;
-		} while (rc == -EAGAIN && tr.again_counter < TRACK_AGAIN_MAX);
+		} while (rc == -EAGAIN && ++tr.again_counter < TRACK_AGAIN_MAX);
 	if (rc == -EAGAIN && tr.again_counter >= TRACK_AGAIN_MAX)
 		rc = -EIO;
 	if (rc) {
@@ -1545,16 +1530,13 @@ static int zsecsendcprb_ioctl(struct ap_perms *perms, unsigned long arg)
 
 	do {
 		rc = _zcrypt_send_cprb(true, perms, &tr, &xcrb);
-		if (rc == -EAGAIN)
-			tr.again_counter++;
-	} while (rc == -EAGAIN && tr.again_counter < TRACK_AGAIN_MAX);
-	/* on failure: retry once again after a requested rescan */
-	if ((rc == -ENODEV) && (zcrypt_process_rescan()))
+	} while (rc == -EAGAIN && ++tr.again_counter < TRACK_AGAIN_MAX);
+
+	/* on ENODEV failure: retry once again after a requested rescan */
+	if (rc == -ENODEV && zcrypt_process_rescan())
 		do {
 			rc = _zcrypt_send_cprb(true, perms, &tr, &xcrb);
-			if (rc == -EAGAIN)
-				tr.again_counter++;
-		} while (rc == -EAGAIN && tr.again_counter < TRACK_AGAIN_MAX);
+		} while (rc == -EAGAIN && ++tr.again_counter < TRACK_AGAIN_MAX);
 	if (rc == -EAGAIN && tr.again_counter >= TRACK_AGAIN_MAX)
 		rc = -EIO;
 	if (rc)
@@ -1578,16 +1560,13 @@ static int zsendep11cprb_ioctl(struct ap_perms *perms, unsigned long arg)
 
 	do {
 		rc = _zcrypt_send_ep11_cprb(true, perms, &tr, &xcrb);
-		if (rc == -EAGAIN)
-			tr.again_counter++;
-	} while (rc == -EAGAIN && tr.again_counter < TRACK_AGAIN_MAX);
-	/* on failure: retry once again after a requested rescan */
-	if ((rc == -ENODEV) && (zcrypt_process_rescan()))
+	} while (rc == -EAGAIN && ++tr.again_counter < TRACK_AGAIN_MAX);
+
+	/* on ENODEV failure: retry once again after a requested rescan */
+	if (rc == -ENODEV && zcrypt_process_rescan())
 		do {
 			rc = _zcrypt_send_ep11_cprb(true, perms, &tr, &xcrb);
-			if (rc == -EAGAIN)
-				tr.again_counter++;
-		} while (rc == -EAGAIN && tr.again_counter < TRACK_AGAIN_MAX);
+		} while (rc == -EAGAIN && ++tr.again_counter < TRACK_AGAIN_MAX);
 	if (rc == -EAGAIN && tr.again_counter >= TRACK_AGAIN_MAX)
 		rc = -EIO;
 	if (rc)
@@ -1758,16 +1737,13 @@ static long trans_modexpo32(struct ap_perms *perms, struct file *filp,
 	mex64.n_modulus = compat_ptr(mex32.n_modulus);
 	do {
 		rc = zcrypt_rsa_modexpo(perms, &tr, &mex64);
-		if (rc == -EAGAIN)
-			tr.again_counter++;
-	} while (rc == -EAGAIN && tr.again_counter < TRACK_AGAIN_MAX);
-	/* on failure: retry once again after a requested rescan */
-	if ((rc == -ENODEV) && (zcrypt_process_rescan()))
+	} while (rc == -EAGAIN && ++tr.again_counter < TRACK_AGAIN_MAX);
+
+	/* on ENODEV failure: retry once again after a requested rescan */
+	if (rc == -ENODEV && zcrypt_process_rescan())
 		do {
 			rc = zcrypt_rsa_modexpo(perms, &tr, &mex64);
-			if (rc == -EAGAIN)
-				tr.again_counter++;
-		} while (rc == -EAGAIN && tr.again_counter < TRACK_AGAIN_MAX);
+		} while (rc == -EAGAIN && ++tr.again_counter < TRACK_AGAIN_MAX);
 	if (rc == -EAGAIN && tr.again_counter >= TRACK_AGAIN_MAX)
 		rc = -EIO;
 	if (rc)
@@ -1811,16 +1787,13 @@ static long trans_modexpo_crt32(struct ap_perms *perms, struct file *filp,
 	crt64.u_mult_inv = compat_ptr(crt32.u_mult_inv);
 	do {
 		rc = zcrypt_rsa_crt(perms, &tr, &crt64);
-		if (rc == -EAGAIN)
-			tr.again_counter++;
-	} while (rc == -EAGAIN && tr.again_counter < TRACK_AGAIN_MAX);
-	/* on failure: retry once again after a requested rescan */
-	if ((rc == -ENODEV) && (zcrypt_process_rescan()))
+	} while (rc == -EAGAIN && ++tr.again_counter < TRACK_AGAIN_MAX);
+
+	/* on ENODEV failure: retry once again after a requested rescan */
+	if (rc == -ENODEV && zcrypt_process_rescan())
 		do {
 			rc = zcrypt_rsa_crt(perms, &tr, &crt64);
-			if (rc == -EAGAIN)
-				tr.again_counter++;
-		} while (rc == -EAGAIN && tr.again_counter < TRACK_AGAIN_MAX);
+		} while (rc == -EAGAIN && ++tr.again_counter < TRACK_AGAIN_MAX);
 	if (rc == -EAGAIN && tr.again_counter >= TRACK_AGAIN_MAX)
 		rc = -EIO;
 	if (rc)
@@ -1883,16 +1856,13 @@ static long trans_xcrb32(struct ap_perms *perms, struct file *filp,
 	xcrb64.status = xcrb32.status;
 	do {
 		rc = _zcrypt_send_cprb(true, perms, &tr, &xcrb64);
-		if (rc == -EAGAIN)
-			tr.again_counter++;
-	} while (rc == -EAGAIN && tr.again_counter < TRACK_AGAIN_MAX);
-	/* on failure: retry once again after a requested rescan */
-	if ((rc == -ENODEV) && (zcrypt_process_rescan()))
+	} while (rc == -EAGAIN && ++tr.again_counter < TRACK_AGAIN_MAX);
+
+	/* on ENODEV failure: retry once again after a requested rescan */
+	if (rc == -ENODEV && zcrypt_process_rescan())
 		do {
 			rc = _zcrypt_send_cprb(true, perms, &tr, &xcrb64);
-			if (rc == -EAGAIN)
-				tr.again_counter++;
-		} while (rc == -EAGAIN && tr.again_counter < TRACK_AGAIN_MAX);
+		} while (rc == -EAGAIN && ++tr.again_counter < TRACK_AGAIN_MAX);
 	if (rc == -EAGAIN && tr.again_counter >= TRACK_AGAIN_MAX)
 		rc = -EIO;
 	xcrb32.reply_control_blk_length = xcrb64.reply_control_blk_length;
@@ -1964,8 +1934,8 @@ static int zcrypt_rng_data_read(struct hwrng *rng, u32 *data)
 	 */
 	if (zcrypt_rng_buffer_index == 0) {
 		rc = zcrypt_rng((char *)zcrypt_rng_buffer);
-		/* on failure: retry once again after a requested rescan */
-		if ((rc == -ENODEV) && (zcrypt_process_rescan()))
+		/* on ENODEV failure: retry once again after an AP bus rescan */
+		if (rc == -ENODEV && zcrypt_process_rescan())
 			rc = zcrypt_rng((char *)zcrypt_rng_buffer);
 		if (rc < 0)
 			return -EIO;
@@ -2027,7 +1997,7 @@ void zcrypt_rng_device_remove(void)
  * an asynchronous job. This function waits until these initial jobs
  * are done and so the zcrypt api should be ready to serve crypto
  * requests - if there are resources available. The function uses an
- * internal timeout of 60s. The very first caller will either wait for
+ * internal timeout of 30s. The very first caller will either wait for
  * ap bus bindings complete or the timeout happens. This state will be
  * remembered for further callers which will only be blocked until a
  * decision is made (timeout or bindings complete).
@@ -2047,7 +2017,7 @@ int zcrypt_wait_api_operational(void)
 	case 0:
 		/* initial state, invoke wait for the ap bus complete */
 		rc = ap_wait_apqn_bindings_complete(
-			msecs_to_jiffies(60 * 1000));
+			msecs_to_jiffies(ZCRYPT_WAIT_BINDINGS_COMPLETE_MS));
 		switch (rc) {
 		case 0:
 			/* ap bus bindings are complete */
diff --git a/drivers/s390/crypto/zcrypt_api.h b/drivers/s390/crypto/zcrypt_api.h
index de659954c8f7..4ed481df57ca 100644
--- a/drivers/s390/crypto/zcrypt_api.h
+++ b/drivers/s390/crypto/zcrypt_api.h
@@ -38,6 +38,15 @@
  */
 #define ZCRYPT_RNG_BUFFER_SIZE	4096
 
+/**
+ * The zcrypt_wait_api_operational() function waits this
+ * amount in milliseconds for ap_wait_aqpn_bindings_complete().
+ * Also on a cprb send failure with ENODEV the send functions
+ * trigger an ap bus rescan and wait this time in milliseconds
+ * for ap_wait_aqpn_bindings_complete() before resending.
+ */
+#define ZCRYPT_WAIT_BINDINGS_COMPLETE_MS 30000
+
 /*
  * Identifier for Crypto Request Performance Index
  */
diff --git a/drivers/s390/crypto/zcrypt_error.h b/drivers/s390/crypto/zcrypt_error.h
index a44fcfcec938..46e27b43a8af 100644
--- a/drivers/s390/crypto/zcrypt_error.h
+++ b/drivers/s390/crypto/zcrypt_error.h
@@ -119,10 +119,9 @@ static inline int convert_error(struct zcrypt_queue *zq,
 	case REP82_ERROR_MESSAGE_TYPE:		 /* 0x20 */
 	case REP82_ERROR_TRANSPORT_FAIL:	 /* 0x90 */
 		/*
-		 * Msg to wrong type or card/infrastructure failure.
-		 * Trigger rescan of the ap bus, trigger retry request.
+		 * Msg to wrong type or card/infrastructure failure. Return
+		 * EAGAIN, the upper layer may do a retry on the request.
 		 */
-		atomic_set(&zcrypt_rescan_req, 1);
 		/* For type 86 response show the apfs value (failure reason) */
 		if (ehdr->reply_code == REP82_ERROR_TRANSPORT_FAIL &&
 		    ehdr->type == TYPE86_RSP_CODE) {