KVM: PPC: Book3S HV: Add fast real-mode H_RANDOM implementation.

Some PowerNV systems include a hardware random-number generator.
This HWRNG is present on POWER7+ and POWER8 chips and is capable of
generating one 64-bit random number every microsecond.  The random
numbers are produced by sampling a set of 64 unstable high-frequency
oscillators and are almost completely entropic.

PAPR defines an H_RANDOM hypercall which guests can use to obtain one
64-bit random sample from the HWRNG.  This adds a real-mode
implementation of the H_RANDOM hypercall.  This hypercall was
implemented in real mode because the latency of reading the HWRNG is
generally small compared to the latency of a guest exit and entry for
all the threads in the same virtual core.

Userspace can detect the presence of the HWRNG and the H_RANDOM
implementation by querying the KVM_CAP_PPC_HWRNG capability.  The
H_RANDOM hypercall implementation will only be invoked when the guest
does an H_RANDOM hypercall if userspace first enables the in-kernel
H_RANDOM implementation using the KVM_CAP_PPC_ENABLE_HCALL capability.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/platforms/powernv/rng.c

@@ -24,12 +24,22 @@
 
 struct powernv_rng {
 	void __iomem *regs;
+	void __iomem *regs_real;
 	unsigned long mask;
 };
 
 static DEFINE_PER_CPU(struct powernv_rng *, powernv_rng);
 
 
+int powernv_hwrng_present(void)
+{
+	struct powernv_rng *rng;
+
+	rng = get_cpu_var(powernv_rng);
+	put_cpu_var(rng);
+	return rng != NULL;
+}
+
 static unsigned long rng_whiten(struct powernv_rng *rng, unsigned long val)
 {
 	unsigned long parity;
@@ -46,6 +56,17 @@ static unsigned long rng_whiten(struct powernv_rng *rng, unsigned long val)
 	return val;
 }
 
+int powernv_get_random_real_mode(unsigned long *v)
+{
+	struct powernv_rng *rng;
+
+	rng = raw_cpu_read(powernv_rng);
+
+	*v = rng_whiten(rng, in_rm64(rng->regs_real));
+
+	return 1;
+}
+
 int powernv_get_random_long(unsigned long *v)
 {
 	struct powernv_rng *rng;
@@ -80,12 +101,20 @@ static __init void rng_init_per_cpu(struct powernv_rng *rng,
 static __init int rng_create(struct device_node *dn)
 {
 	struct powernv_rng *rng;
+	struct resource res;
 	unsigned long val;
 
 	rng = kzalloc(sizeof(*rng), GFP_KERNEL);
 	if (!rng)
 		return -ENOMEM;
 
+	if (of_address_to_resource(dn, 0, &res)) {
+		kfree(rng);
+		return -ENXIO;
+	}
+
+	rng->regs_real = (void __iomem *)res.start;
+
 	rng->regs = of_iomap(dn, 0);
 	if (!rng->regs) {
 		kfree(rng);