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

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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>
This commit is contained in:
Michael Ellerman
2015-03-20 20:39:41 +11:00
committed by Alexander Graf
parent 99342cf804
commit e928e9cb36
8 changed files with 191 additions and 2 deletions
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3
arch/powerpc/kvm/powerpc.c
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@@ -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