[PATCH] KVM: PPC: Book3S HV: Optimise mmio emulation for devices on FAST_MMIO_BUS

[Paul Mackerras]

On Thu, Feb 07, 2019 at 03:56:50PM +1100, Suraj Jitindar Singh wrote:
> Devices on the KVM_FAST_MMIO_BUS by definition have length zero and are
> thus used for notification purposes rather than data transfer. For
> example eventfd for virtio devices.
> 
> This means that when emulating mmio instructions which target devices on
> this bus we can immediately handle them and return without needing to load
> the instruction from guest memory.
> 
> For now we restrict this to stores as this is the only use case at
> present.
> 
> For a normal guest the effect is negligible, however for a nested guest
> we save on the order of 5us per access.
> 
> Signed-off-by: Suraj Jitindar Singh <sjitindarsingh at gmail.com>

Thanks, applied to my kvm-ppc-next tree.

Paul.