Re: [PATCH v3 1/4] KVM: PPC: Book3S HV: POWER9 does not require secondary thread management

Nicholas Piggin [off-list ref] writes:

POWER9 CPUs have independent MMU contexts per thread, so KVM does not
need to quiesce secondary threads, so the hwthread_req/hwthread_state
protocol does not have to be used. So patch it away on POWER9, and patch
away the branch from the Linux idle wakeup to kvm_start_guest that is
never used.

Add a warning and error out of kvmppc_grab_hwthread in case it is ever
called on POWER9.

This avoids a hwsync in the idle wakeup path on POWER9.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/include/asm/kvm_book3s_asm.h |  4 ++++
 arch/powerpc/kernel/idle_book3s.S         | 35 +++++++++++++++++++++----------
 arch/powerpc/kvm/book3s_hv.c              | 14 ++++++++++++-
 arch/powerpc/kvm/book3s_hv_rmhandlers.S   |  8 +++++++
 4 files changed, 49 insertions(+), 12 deletions(-)

Paulus do you mind acking this and I'll put it in my ppc-kvm topic
branch.

cheers