Re: [PATCH v10 13/19] KVM: s390: pv: destroy the configuration before its memory

[Nico Boehr]

On Thu, 2022-04-14 at 10:03 +0200, Claudio Imbrenda wrote:
> Move the Destroy Secure Configuration UVC before the loop to destroy
> the memory. If the protected VM has memory, it will be cleaned up and
> made accessible by the Destroy Secure Configuraion UVC. The struct
> page for the relevant pages will still have the protected bit set, so
> the loop is still needed to clean that up.
> 
> Switching the order of those two operations does not change the
> outcome, but it is significantly faster.
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>

Reviewed-by: Nico Boehr <nrb@xxxxxxxxxxxxx>

See one tiny thing below.

> diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
> index be3b467f8feb..bd850be08c86 100644
> --- a/arch/s390/kvm/pv.c
> +++ b/arch/s390/kvm/pv.c
[...]
> -       cc = uv_cmd_nodata(kvm_s390_pv_get_handle(kvm),
> -                          UVC_CMD_DESTROY_SEC_CONF, rc, rrc);
>         WRITE_ONCE(kvm->arch.gmap->guest_handle, 0);

Maybe it makes sense to also move the WRITE_ONCE up.