Re: [Qemu-devel] [Qemu-ppc] [RFC] pseries: Enable in-kernel H_LOGICAL_CI_{LOAD, STORE} implementations

[Nikunj A Dadhania]

David Gibson <address@hidden> writes:

> qemu currently implements the hypercalls H_LOGICAL_CI_LOAD and
> H_LOGICAL_CI_STORE as PAPR extensions.  These are used by the SLOF firmware
> for IO, because performing cache inhibited MMIO accesses with the MMU off
> (real mode) is very awkward on POWER.
>
> This approach breaks when SLOF needs to access IO devices implemented
> within KVM instead of in qemu.  The simplest example would be virtio-blk
> using an iothread, because the iothread / dataplane mechanism relies on
> an in-kernel implementation of the virtio queue notification MMIO.
>
> To fix this, an in-kernel implementation of these hypercalls has been made,
> however, the hypercalls still need to be enabled from qemu.  This performs
> the necessary calls to do so.
>
> Signed-off-by: David Gibson <address@hidden>

Reviewed-by: Nikunj A Dadhania <address@hidden>