KVM: PPC: Book3S HV: Add missing break statements in ONE_REG switches

This adds break statements after the KVM_REG_PPC_PPR case in
kvmppc_get_one_reg() and kvmppc_set_one_reg().  The error was
introduced in commit d3ecc54390 ("KVM: PPC: Book3S HV: Support POWER6
compatibility mode on POWER7").  That commit also forgot to update
Documentation/virtual/kvm/api.txt with the new one_reg identifier,
so we do that here too.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
KVM: PPC: Book3S HV: Better handling of exceptions that happen in real mode

When an interrupt or exception happens in the guest that comes to the
host, the CPU goes to hypervisor real mode (MMU off) to handle the
exception but doesn't change the MMU context.  After saving a few
registers, we then clear the "in guest" flag.  If, for any reason,
we get an exception in the real-mode code, that then gets handled
by the normal kernel exception handlers, which turn the MMU on.  This
is disastrous if the MMU is still set to the guest context, since we
end up executing instructions from random places in the guest kernel
with hypervisor privilege.

In order to catch this situation, we define a new value for the "in guest"
flag, KVM_GUEST_MODE_HOST_HV, to indicate that we are in hypervisor real
mode with guest MMU context.  If the "in guest" flag is set to this value,
we branch off to an emergency handler.  For the moment, this just does
a branch to self to stop the CPU from doing anything further.

While we're here, we define another new flag value to indicate that we
are in a HV guest, as distinct from a PR guest.  This will be useful
when we have a kernel that can support both PR and HV guests concurrently.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>