Re: [PATCH] spapr: prevent hdec timer being set up under virtual hypervisor

[Cédric Le Goater]

On 2/14/22 14:32, Fabiano Rosas wrote:
> Nicholas Piggin <npiggin@gmail.com> writes:
>
> > The spapr virtual hypervisor does not require the hdecr timer.
>
> Why is that? Is this not needed for an emulated powernv running KVM
> guests?

It is now also running in the QEMU pseries machine (L0) when a
nested is running. That's part of the implementation Nick did for
the KVM-on-pseries-in-QEMU-TCG.

But isn't that redundant with the cpu_ppc_hdecr_init() and
cpu_ppc_hdecr_exit() from the RFC ? and shouldn't that be
created only once, when the first nested is started or when
the machine is if cap-nested-hv=on ?

> > Remove it.
> >
> > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> > ---
> >   hw/ppc/ppc.c            | 2 +-
> >   hw/ppc/spapr_cpu_core.c | 6 +++---
> >   2 files changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/hw/ppc/ppc.c b/hw/ppc/ppc.c
> > index 462c87dba8..a7c262db93 100644
> > --- a/hw/ppc/ppc.c
> > +++ b/hw/ppc/ppc.c
> > @@ -1072,7 +1072,7 @@ clk_setup_cb cpu_ppc_tb_init (CPUPPCState *env, uint32_t 
> > freq)
> >       }
> >       /* Create new timer */
> >       tb_env->decr_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, &cpu_ppc_decr_cb, 
> > cpu);
> > -    if (env->has_hv_mode) {
> > +    if (env->has_hv_mode && !cpu->vhyp) {

hmm, Can we have (env->has_hv_mode && cpu->vhyp) ?  this is confusing :/

Thanks,

C.


> >           tb_env->hdecr_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, 
> > &cpu_ppc_hdecr_cb,
> >                                                   cpu);
> >       } else {
> > diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
> > index a781e97f8d..ed84713960 100644
> > --- a/hw/ppc/spapr_cpu_core.c
> > +++ b/hw/ppc/spapr_cpu_core.c
> > @@ -261,12 +261,12 @@ static bool spapr_realize_vcpu(PowerPCCPU *cpu, 
> > SpaprMachineState *spapr,
> >           return false;
> >       }
> >   
> > -    /* Set time-base frequency to 512 MHz */
> > -    cpu_ppc_tb_init(env, SPAPR_TIMEBASE_FREQ);
> > -
> >       cpu_ppc_set_vhyp(cpu, PPC_VIRTUAL_HYPERVISOR(spapr));
> >       kvmppc_set_papr(cpu);
> >   
> > +    /* Set time-base frequency to 512 MHz. vhyp must be set first. */
> > +    cpu_ppc_tb_init(env, SPAPR_TIMEBASE_FREQ);
> > +
> >       if (spapr_irq_cpu_intc_create(spapr, cpu, errp) < 0) {
> >           qdev_unrealize(DEVICE(cpu));
> >           return false;