Re: [PATCH 4/5] KVM: PPC: Book3S HV: Add fast real-mode H_RANDOM implementation.

[Alexander Graf <agraf@suse.de>]

On 03.12.14 03:30, Paul Mackerras wrote:
> From: Michael Ellerman <michael@ellerman.id.au>
> 
> 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 quering 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>

This conflicts with the per-cpu cleanups. I've pulled the patch from my
queue. Please rebase it once we've got everything merged together and
resubmit.


Alex