[PATCH v4 1/4] s390/crypto: Replace cond_resched() with msleep(1)

[Heiko Carstens <hca@linux.ibm.com>]

From: Peter Zijlstra <peterz@infradead.org>

With [1] cond_resched() is always compiled away and becomes a no-op.

The comments for all cond_resched() calls in crypto code however indicate
that the current process should be scheduled away to avoid instant
re-invocation of a callback. This is not what cond_resched() would do or
did.

Instead of just removing the cond_resched() calls, replace them with
msleep() calls, as suggested by Holger Dengler. This forces the current
task to be scheduled away (sleeps) like originally intended.

Holger provided information why this intended [2]:
"
Let me give a bit of background here: The protected key can only get
invalid, if the Linux instance (z/VM or KVM guest) is moved to another
hypervisor on a different machine (aka life guest relocation). In such a
case, the crypto accelerator card and the host has to exchange the "real
key", which is wrapped by the host and handed back to the guest as the
re-newed protected key. Unfortunately there is no asynchronous trigger
on completion, you have to re-try (and maybe get another "in progress"
return).

And as if that weren't bad enough, if this key exchange between card and
host is the first one, card and host has to instantiate a secure
communication channel (including a key exchange for the transport layer).
"

[1] commit 7dadeaa6e851 ("sched: Further restrict the preemption modes")
[2] https://lore.kernel.org/all/39570813-27b0-40f9-89c5-8e2dce05e2f0@linux.ibm.com/
[3] https://lore.kernel.org/all/20260731084027.GE776954@noisy.programming.kicks-ass.net/

[hca@linux.ibm.com: took Peter's patch [3] and provided commit message]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
 arch/s390/crypto/paes_s390.c  | 44 ++++-------------------------------
 arch/s390/crypto/phmac_s390.c | 25 +++-----------------
 arch/s390/include/asm/pkey.h  | 16 +++++++++++++
 3 files changed, 23 insertions(+), 62 deletions(-)

diff --git a/arch/s390/crypto/paes_s390.c b/arch/s390/crypto/paes_s390.c
index 8cfe6166c193..973436592318 100644
--- a/arch/s390/crypto/paes_s390.c
+++ b/arch/s390/crypto/paes_s390.c
@@ -548,16 +548,7 @@ static int ecb_paes_do_one_request(struct crypto_engine *engine, void *areq)
 
 	rc = ecb_paes_do_crypt(ctx, req_ctx, tested, true);
 	if (rc == -EKEYEXPIRED) {
-		/*
-		 * Protected key expired, conversion is in process.
-		 * Trigger a re-schedule of this request by returning
-		 * -ENOSPC ("hardware queue is full") to the crypto engine.
-		 * To avoid immediately re-invocation of this callback,
-		 * tell the scheduler to voluntarily give up the CPU here.
-		 */
-		cond_resched();
-		pr_debug("rescheduling request\n");
-		return -ENOSPC;
+		return pkey_handle_expired();
 	} else if (rc) {
 		skcipher_walk_done(walk, rc);
 	}
@@ -814,16 +805,7 @@ static int cbc_paes_do_one_request(struct crypto_engine *engine, void *areq)
 
 	rc = cbc_paes_do_crypt(ctx, req_ctx, tested, true);
 	if (rc == -EKEYEXPIRED) {
-		/*
-		 * Protected key expired, conversion is in process.
-		 * Trigger a re-schedule of this request by returning
-		 * -ENOSPC ("hardware queue is full") to the crypto engine.
-		 * To avoid immediately re-invocation of this callback,
-		 * tell the scheduler to voluntarily give up the CPU here.
-		 */
-		cond_resched();
-		pr_debug("rescheduling request\n");
-		return -ENOSPC;
+		return pkey_handle_expired();
 	} else if (rc) {
 		skcipher_walk_done(walk, rc);
 	}
@@ -1122,16 +1104,7 @@ static int ctr_paes_do_one_request(struct crypto_engine *engine, void *areq)
 
 	rc = ctr_paes_do_crypt(ctx, req_ctx, tested, true);
 	if (rc == -EKEYEXPIRED) {
-		/*
-		 * Protected key expired, conversion is in process.
-		 * Trigger a re-schedule of this request by returning
-		 * -ENOSPC ("hardware queue is full") to the crypto engine.
-		 * To avoid immediately re-invocation of this callback,
-		 * tell the scheduler to voluntarily give up the CPU here.
-		 */
-		cond_resched();
-		pr_debug("rescheduling request\n");
-		return -ENOSPC;
+		return pkey_handle_expired();
 	} else if (rc) {
 		skcipher_walk_done(walk, rc);
 	}
@@ -1565,16 +1538,7 @@ static int xts_paes_do_one_request(struct crypto_engine *engine, void *areq)
 
 	rc = xts_paes_do_crypt(ctx, req_ctx, tested, true);
 	if (rc == -EKEYEXPIRED) {
-		/*
-		 * Protected key expired, conversion is in process.
-		 * Trigger a re-schedule of this request by returning
-		 * -ENOSPC ("hardware queue is full") to the crypto engine.
-		 * To avoid immediately re-invocation of this callback,
-		 * tell the scheduler to voluntarily give up the CPU here.
-		 */
-		cond_resched();
-		pr_debug("rescheduling request\n");
-		return -ENOSPC;
+		return pkey_handle_expired();
 	} else if (rc) {
 		skcipher_walk_done(walk, rc);
 	}
diff --git a/arch/s390/crypto/phmac_s390.c b/arch/s390/crypto/phmac_s390.c
index 03ca33ffe6cc..020a1beb2e22 100644
--- a/arch/s390/crypto/phmac_s390.c
+++ b/arch/s390/crypto/phmac_s390.c
@@ -887,16 +887,7 @@ static int phmac_do_one_request(struct crypto_engine *engine, void *areq)
 	case OP_FINUP:
 		rc = phmac_kmac_update(req, true);
 		if (rc == -EKEYEXPIRED) {
-			/*
-			 * Protected key expired, conversion is in process.
-			 * Trigger a re-schedule of this request by returning
-			 * -ENOSPC ("hardware queue full") to the crypto engine.
-			 * To avoid immediately re-invocation of this callback,
-			 * tell scheduler to voluntarily give up the CPU here.
-			 */
-			pr_debug("rescheduling request\n");
-			cond_resched();
-			return -ENOSPC;
+			return pkey_handle_expired();
 		} else if (rc) {
 			hwh_advance(hwh, rc);
 			goto out;
@@ -907,18 +898,8 @@ static int phmac_do_one_request(struct crypto_engine *engine, void *areq)
 		fallthrough;
 	case OP_FINAL:
 		rc = phmac_kmac_final(req, true);
-		if (rc == -EKEYEXPIRED) {
-			/*
-			 * Protected key expired, conversion is in process.
-			 * Trigger a re-schedule of this request by returning
-			 * -ENOSPC ("hardware queue full") to the crypto engine.
-			 * To avoid immediately re-invocation of this callback,
-			 * tell scheduler to voluntarily give up the CPU here.
-			 */
-			pr_debug("rescheduling request\n");
-			cond_resched();
-			return -ENOSPC;
-		}
+		if (rc == -EKEYEXPIRED)
+			return pkey_handle_expired();
 		break;
 	default:
 		/* unknown/unsupported/unimplemented asynch op */
diff --git a/arch/s390/include/asm/pkey.h b/arch/s390/include/asm/pkey.h
index 0af5ac4f646b..82e403322e89 100644
--- a/arch/s390/include/asm/pkey.h
+++ b/arch/s390/include/asm/pkey.h
@@ -13,6 +13,7 @@
 
 #include <linux/ioctl.h>
 #include <linux/types.h>
+#include <linux/delay.h>
 #include <uapi/asm/pkey.h>
 
 /*
@@ -44,4 +45,19 @@ int pkey_key2protkey(const u8 *key, u32 keylen,
  */
 #define PKEY_XFLAG_NOCLEARKEY 0x0002
 
+static inline int pkey_handle_expired(void)
+{
+	/*
+	 * Protected key expired due to relocation to another host. The long
+	 * running re-wrap has no asynchronous completion notification, so
+	 * polling is required. Trigger a re-schedule of this request by
+	 * returning -ENOSPC ("hardware queue full") to the crypto engine.
+	 * To avoid immediately re-invocation of this callback,
+	 * tell the scheduler to voluntarily give up the CPU here.
+	 */
+	msleep(1);
+	pr_debug("rescheduling request\n");
+	return -ENOSPC;
+}
+
 #endif /* _KAPI_PKEY_H */
-- 
2.53.0