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

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Mon, 30 May 2022 09:37:37 +0200
Nico Boehr <nrb@linux.ibm.com> wrote:

> 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@linux.ibm.com>  
> 
> Reviewed-by: Nico Boehr <nrb@linux.ibm.com>
> 
> 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.

yes, I'll move it up, so that it is right after the UVC again