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>

3 files changed, 133 insertions, 0 deletions

diff --git a/arch/powerpc/kvm/book3s_hv_builtin.c b/arch/powerpc/kvm/book3s_hv_builtin.c
index 1f083ff8a61a..1954a1c4b1f9 100644
--- a/arch/powerpc/kvm/book3s_hv_builtin.c
+++ b/arch/powerpc/kvm/book3s_hv_builtin.c
@@ -21,6 +21,7 @@
 #include <asm/cputable.h>
 #include <asm/kvm_ppc.h>
 #include <asm/kvm_book3s.h>
+#include <asm/archrandom.h>
 
 #define KVM_CMA_CHUNK_ORDER	18
 
@@ -169,3 +170,17 @@ int kvmppc_hcall_impl_hv_realmode(unsigned long cmd)
 	return 0;
 }
 EXPORT_SYMBOL_GPL(kvmppc_hcall_impl_hv_realmode);
+
+int kvmppc_hwrng_present(void)
+{
+	return powernv_hwrng_present();
+}
+EXPORT_SYMBOL_GPL(kvmppc_hwrng_present);
+
+long kvmppc_h_random(struct kvm_vcpu *vcpu)
+{
+	if (powernv_get_random_real_mode(&vcpu->arch.gpr[4]))
+		return H_SUCCESS;
+
+	return H_HARDWARE;
+}
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index 6cbf1630cb70..0814ca122fcd 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -1839,6 +1839,121 @@ hcall_real_table:
 	.long	0		/* 0x12c */
 	.long	0		/* 0x130 */
 	.long	DOTSYM(kvmppc_h_set_xdabr) - hcall_real_table
+	.long	0		/* 0x138 */
+	.long	0		/* 0x13c */
+	.long	0		/* 0x140 */
+	.long	0		/* 0x144 */
+	.long	0		/* 0x148 */
+	.long	0		/* 0x14c */
+	.long	0		/* 0x150 */
+	.long	0		/* 0x154 */
+	.long	0		/* 0x158 */
+	.long	0		/* 0x15c */
+	.long	0		/* 0x160 */
+	.long	0		/* 0x164 */
+	.long	0		/* 0x168 */
+	.long	0		/* 0x16c */
+	.long	0		/* 0x170 */
+	.long	0		/* 0x174 */
+	.long	0		/* 0x178 */
+	.long	0		/* 0x17c */
+	.long	0		/* 0x180 */
+	.long	0		/* 0x184 */
+	.long	0		/* 0x188 */
+	.long	0		/* 0x18c */
+	.long	0		/* 0x190 */
+	.long	0		/* 0x194 */
+	.long	0		/* 0x198 */
+	.long	0		/* 0x19c */
+	.long	0		/* 0x1a0 */
+	.long	0		/* 0x1a4 */
+	.long	0		/* 0x1a8 */
+	.long	0		/* 0x1ac */
+	.long	0		/* 0x1b0 */
+	.long	0		/* 0x1b4 */
+	.long	0		/* 0x1b8 */
+	.long	0		/* 0x1bc */
+	.long	0		/* 0x1c0 */
+	.long	0		/* 0x1c4 */
+	.long	0		/* 0x1c8 */
+	.long	0		/* 0x1cc */
+	.long	0		/* 0x1d0 */
+	.long	0		/* 0x1d4 */
+	.long	0		/* 0x1d8 */
+	.long	0		/* 0x1dc */
+	.long	0		/* 0x1e0 */
+	.long	0		/* 0x1e4 */
+	.long	0		/* 0x1e8 */
+	.long	0		/* 0x1ec */
+	.long	0		/* 0x1f0 */
+	.long	0		/* 0x1f4 */
+	.long	0		/* 0x1f8 */
+	.long	0		/* 0x1fc */
+	.long	0		/* 0x200 */
+	.long	0		/* 0x204 */
+	.long	0		/* 0x208 */
+	.long	0		/* 0x20c */
+	.long	0		/* 0x210 */
+	.long	0		/* 0x214 */
+	.long	0		/* 0x218 */
+	.long	0		/* 0x21c */
+	.long	0		/* 0x220 */
+	.long	0		/* 0x224 */
+	.long	0		/* 0x228 */
+	.long	0		/* 0x22c */
+	.long	0		/* 0x230 */
+	.long	0		/* 0x234 */
+	.long	0		/* 0x238 */
+	.long	0		/* 0x23c */
+	.long	0		/* 0x240 */
+	.long	0		/* 0x244 */
+	.long	0		/* 0x248 */
+	.long	0		/* 0x24c */
+	.long	0		/* 0x250 */
+	.long	0		/* 0x254 */
+	.long	0		/* 0x258 */
+	.long	0		/* 0x25c */
+	.long	0		/* 0x260 */
+	.long	0		/* 0x264 */
+	.long	0		/* 0x268 */
+	.long	0		/* 0x26c */
+	.long	0		/* 0x270 */
+	.long	0		/* 0x274 */
+	.long	0		/* 0x278 */
+	.long	0		/* 0x27c */
+	.long	0		/* 0x280 */
+	.long	0		/* 0x284 */
+	.long	0		/* 0x288 */
+	.long	0		/* 0x28c */
+	.long	0		/* 0x290 */
+	.long	0		/* 0x294 */
+	.long	0		/* 0x298 */
+	.long	0		/* 0x29c */
+	.long	0		/* 0x2a0 */
+	.long	0		/* 0x2a4 */
+	.long	0		/* 0x2a8 */
+	.long	0		/* 0x2ac */
+	.long	0		/* 0x2b0 */
+	.long	0		/* 0x2b4 */
+	.long	0		/* 0x2b8 */
+	.long	0		/* 0x2bc */
+	.long	0		/* 0x2c0 */
+	.long	0		/* 0x2c4 */
+	.long	0		/* 0x2c8 */
+	.long	0		/* 0x2cc */
+	.long	0		/* 0x2d0 */
+	.long	0		/* 0x2d4 */
+	.long	0		/* 0x2d8 */
+	.long	0		/* 0x2dc */
+	.long	0		/* 0x2e0 */
+	.long	0		/* 0x2e4 */
+	.long	0		/* 0x2e8 */
+	.long	0		/* 0x2ec */
+	.long	0		/* 0x2f0 */
+	.long	0		/* 0x2f4 */
+	.long	0		/* 0x2f8 */
+	.long	0		/* 0x2fc */
+	.long	DOTSYM(kvmppc_h_random) - hcall_real_table
 	.globl	hcall_real_table_end
 hcall_real_table_end:
 
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 24bfe401373e..55a4763d6d11 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -529,6 +529,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_PPC_RMA:
 		r = 0;
 		break;
+	case KVM_CAP_PPC_HWRNG:
+		r = kvmppc_hwrng_present();
+		break;
 #endif
 	case KVM_CAP_SYNC_MMU:
 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE