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>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index f574d7be7631..4b60056776d1 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -813,6 +813,7 @@ struct kvm_ppc_smmu_info {
 #define KVM_CAP_MIPS_MSA 112
 #define KVM_CAP_S390_INJECT_IRQ 113
 #define KVM_CAP_S390_IRQ_STATE 114
+#define KVM_CAP_PPC_HWRNG 115
 
 #ifdef KVM_CAP_IRQ_ROUTING