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Re: [Qemu-devel] [PATCH] spapr: Correct compatibility mode setting for h
From: |
David Gibson |
Subject: |
Re: [Qemu-devel] [PATCH] spapr: Correct compatibility mode setting for hotplugged CPUs |
Date: |
Fri, 12 Jan 2018 12:47:34 +1100 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
On Thu, Jan 11, 2018 at 01:24:30PM +0100, Greg Kurz wrote:
> On Fri, 5 Jan 2018 14:07:29 +1100
> David Gibson <address@hidden> wrote:
>
> > On Thu, Jan 04, 2018 at 06:47:18PM +0100, Greg Kurz wrote:
> > > On Thu, 4 Jan 2018 15:24:05 +1100
> > > David Gibson <address@hidden> wrote:
> > >
> > > > Currently the pseries machine sets the compatibility mode for the
> > > > guest's cpus in two places: 1) at machine reset and 2) after CAS
> > > > negotiation.
> > > >
> > > > This means that if we set or negotiate a compatiblity mode, then
> > > > hotplug a cpu, the hotplugged cpu doesn't get the right mode set and
> > > > will incorrectly have the full native features.
> > > >
> > > > To correct this, we set the compatibility mode on a cpu when it is
> > > > brought online with the 'start-cpu' RTAS call. Given that we no
> > > > longer need to set the compatibility mode on all CPUs at machine
> > > > reset, so we change that to only set the mode for the boot cpu.
> > > >
> > > > Signed-off-by: David Gibson <address@hidden>
> > > > ---
> > > > hw/ppc/spapr.c | 2 +-
> > > > hw/ppc/spapr_rtas.c | 8 ++++++++
> > > > 2 files changed, 9 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > > > index e22888ba06..d1acfe8858 100644
> > > > --- a/hw/ppc/spapr.c
> > > > +++ b/hw/ppc/spapr.c
> > > > @@ -1510,7 +1510,7 @@ static void spapr_machine_reset(void)
> > > > spapr_ovec_cleanup(spapr->ov5_cas);
> > > > spapr->ov5_cas = spapr_ovec_new();
> > > >
> > > > - ppc_set_compat_all(spapr->max_compat_pvr, &error_fatal);
> > > > + ppc_set_compat(first_ppc_cpu, spapr->max_compat_pvr,
> > > > &error_fatal);
> > > > }
> > > >
> > > > fdt = spapr_build_fdt(spapr, rtas_addr, spapr->rtas_size);
> > > > diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
> > > > index 4bb939d3d1..2ed00548c1 100644
> > > > --- a/hw/ppc/spapr_rtas.c
> > > > +++ b/hw/ppc/spapr_rtas.c
> > > > @@ -163,6 +163,7 @@ static void rtas_start_cpu(PowerPCCPU *cpu_,
> > > > sPAPRMachineState *spapr,
> > > > CPUState *cs = CPU(cpu);
> > > > CPUPPCState *env = &cpu->env;
> > > > PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);
> > > > + Error *local_err = NULL;
> > > >
> > > > if (!cs->halted) {
> > > > rtas_st(rets, 0, RTAS_OUT_HW_ERROR);
> > > > @@ -174,6 +175,13 @@ static void rtas_start_cpu(PowerPCCPU *cpu_,
> > > > sPAPRMachineState *spapr,
> > > > * new cpu enters */
> > > > kvm_cpu_synchronize_state(cs);
> > > >
> > > > + /* Set compatibility mode to match existing cpus */
> > > > + ppc_set_compat(cpu, POWERPC_CPU(first_cpu)->compat_pvr,
> > > > &local_err);
> > >
> > > Is it okay to report a simple HW error to the guest here instead of
> > > aborting
> > > like we do with first_cpu at reset time ?
> >
> > Should be: this happens before we turn the cpu on, so the effect will
> > be that the guest fails to online the cpu. That seems like a better
> > failure mode than killing the already running guest.
> >
>
> Of course, I generally agree with the "better failure mode". My point was
> just that if we managed to set the compat mode with the first cpu but we
> fail to propagate the same compat mode to subsequent cpus, then this is
> a bug in QEMU or KVM.
Ah, I see your point. Yes, I guess that's true. Nonetheless, I think
the better failure mode is still a better idea, even if something goes
wrong elsewhere.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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