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

From: Michael Ellerman <[email-masked]>
Date: Mon, 28 Aug 2017 21:49:44 +1000

Nicholas Piggin <[email-masked]> 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 <[email-masked]>
> ---
>  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