v4.19.13 snapshot.
diff --git a/arch/s390/crypto/arch_random.c b/arch/s390/crypto/arch_random.c
new file mode 100644
index 0000000..dd95cdb
--- /dev/null
+++ b/arch/s390/crypto/arch_random.c
@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * s390 arch random implementation.
+ *
+ * Copyright IBM Corp. 2017, 2018
+ * Author(s): Harald Freudenberger
+ *
+ * The s390_arch_random_generate() function may be called from random.c
+ * in interrupt context. So this implementation does the best to be very
+ * fast. There is a buffer of random data which is asynchronously checked
+ * and filled by a workqueue thread.
+ * If there are enough bytes in the buffer the s390_arch_random_generate()
+ * just delivers these bytes. Otherwise false is returned until the
+ * worker thread refills the buffer.
+ * The worker fills the rng buffer by pulling fresh entropy from the
+ * high quality (but slow) true hardware random generator. This entropy
+ * is then spread over the buffer with an pseudo random generator PRNG.
+ * As the arch_get_random_seed_long() fetches 8 bytes and the calling
+ * function add_interrupt_randomness() counts this as 1 bit entropy the
+ * distribution needs to make sure there is in fact 1 bit entropy contained
+ * in 8 bytes of the buffer. The current values pull 32 byte entropy
+ * and scatter this into a 2048 byte buffer. So 8 byte in the buffer
+ * will contain 1 bit of entropy.
+ * The worker thread is rescheduled based on the charge level of the
+ * buffer but at least with 500 ms delay to avoid too much CPU consumption.
+ * So the max. amount of rng data delivered via arch_get_random_seed is
+ * limited to 4k bytes per second.
+ */
+
+#include <linux/kernel.h>
+#include <linux/atomic.h>
+#include <linux/random.h>
+#include <linux/slab.h>
+#include <linux/static_key.h>
+#include <linux/workqueue.h>
+#include <asm/cpacf.h>
+
+DEFINE_STATIC_KEY_FALSE(s390_arch_random_available);
+
+atomic64_t s390_arch_random_counter = ATOMIC64_INIT(0);
+EXPORT_SYMBOL(s390_arch_random_counter);
+
+#define ARCH_REFILL_TICKS (HZ/2)
+#define ARCH_PRNG_SEED_SIZE 32
+#define ARCH_RNG_BUF_SIZE 2048
+
+static DEFINE_SPINLOCK(arch_rng_lock);
+static u8 *arch_rng_buf;
+static unsigned int arch_rng_buf_idx;
+
+static void arch_rng_refill_buffer(struct work_struct *);
+static DECLARE_DELAYED_WORK(arch_rng_work, arch_rng_refill_buffer);
+
+bool s390_arch_random_generate(u8 *buf, unsigned int nbytes)
+{
+ /* lock rng buffer */
+ if (!spin_trylock(&arch_rng_lock))
+ return false;
+
+ /* try to resolve the requested amount of bytes from the buffer */
+ arch_rng_buf_idx -= nbytes;
+ if (arch_rng_buf_idx < ARCH_RNG_BUF_SIZE) {
+ memcpy(buf, arch_rng_buf + arch_rng_buf_idx, nbytes);
+ atomic64_add(nbytes, &s390_arch_random_counter);
+ spin_unlock(&arch_rng_lock);
+ return true;
+ }
+
+ /* not enough bytes in rng buffer, refill is done asynchronously */
+ spin_unlock(&arch_rng_lock);
+
+ return false;
+}
+EXPORT_SYMBOL(s390_arch_random_generate);
+
+static void arch_rng_refill_buffer(struct work_struct *unused)
+{
+ unsigned int delay = ARCH_REFILL_TICKS;
+
+ spin_lock(&arch_rng_lock);
+ if (arch_rng_buf_idx > ARCH_RNG_BUF_SIZE) {
+ /* buffer is exhausted and needs refill */
+ u8 seed[ARCH_PRNG_SEED_SIZE];
+ u8 prng_wa[240];
+ /* fetch ARCH_PRNG_SEED_SIZE bytes of entropy */
+ cpacf_trng(NULL, 0, seed, sizeof(seed));
+ /* blow this entropy up to ARCH_RNG_BUF_SIZE with PRNG */
+ memset(prng_wa, 0, sizeof(prng_wa));
+ cpacf_prno(CPACF_PRNO_SHA512_DRNG_SEED,
+ &prng_wa, NULL, 0, seed, sizeof(seed));
+ cpacf_prno(CPACF_PRNO_SHA512_DRNG_GEN,
+ &prng_wa, arch_rng_buf, ARCH_RNG_BUF_SIZE, NULL, 0);
+ arch_rng_buf_idx = ARCH_RNG_BUF_SIZE;
+ }
+ delay += (ARCH_REFILL_TICKS * arch_rng_buf_idx) / ARCH_RNG_BUF_SIZE;
+ spin_unlock(&arch_rng_lock);
+
+ /* kick next check */
+ queue_delayed_work(system_long_wq, &arch_rng_work, delay);
+}
+
+static int __init s390_arch_random_init(void)
+{
+ /* all the needed PRNO subfunctions available ? */
+ if (cpacf_query_func(CPACF_PRNO, CPACF_PRNO_TRNG) &&
+ cpacf_query_func(CPACF_PRNO, CPACF_PRNO_SHA512_DRNG_GEN)) {
+
+ /* alloc arch random working buffer */
+ arch_rng_buf = kmalloc(ARCH_RNG_BUF_SIZE, GFP_KERNEL);
+ if (!arch_rng_buf)
+ return -ENOMEM;
+
+ /* kick worker queue job to fill the random buffer */
+ queue_delayed_work(system_long_wq,
+ &arch_rng_work, ARCH_REFILL_TICKS);
+
+ /* enable arch random to the outside world */
+ static_branch_enable(&s390_arch_random_available);
+ }
+
+ return 0;
+}
+arch_initcall(s390_arch_random_init);