• Michael Ellerman's avatar
    KVM: PPC: Book3S HV: Add fast real-mode H_RANDOM implementation. · e928e9cb
    Michael Ellerman authored
    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: default avatarMichael Ellerman <michael@ellerman.id.au>
    Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
    Signed-off-by: default avatarAlexander Graf <agraf@suse.de>
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