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List:       qemu-ppc
Subject:    Re: [Qemu-ppc] [RFC 02/17] powernv: CPU compatibility modes don't make sense for powernv
From:       David Gibson <david () gibson ! dropbear ! id ! au>
Date:       2016-10-31 8:38:44
Message-ID: 20161031083844.GS18226 () umbus ! fritz ! box
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On Mon, Oct 31, 2016 at 08:46:55AM +0100, Thomas Huth wrote:
> On 30.10.2016 12:11, David Gibson wrote:
> > powernv has some code (derived from the spapr equivalent) used in device
> > tree generation which depends on the CPU's compatibility mode / logical
> > PVR.  However, compatibility modes don't make sense on powernv - at least
> > not as a property controlled by the host - because the guest in powernv
> > has full hypervisor level access to the virtual system, and so owns the
> > PCR (Processor Compatibility Register) which implements compatiblity modes.
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  hw/ppc/pnv.c | 6 +-----
> >  1 file changed, 1 insertion(+), 5 deletions(-)
> > 
> > diff --git a/hw/ppc/pnv.c b/hw/ppc/pnv.c
> > index 82276e0..6af3424 100644
> > --- a/hw/ppc/pnv.c
> > +++ b/hw/ppc/pnv.c
> > @@ -110,7 +110,7 @@ static void powernv_create_core_node(PnvChip *chip, PnvCore *pc, void *fdt)
> >      CPUState *cs = CPU(DEVICE(pc->threads));
> >      DeviceClass *dc = DEVICE_GET_CLASS(cs);
> >      PowerPCCPU *cpu = POWERPC_CPU(cs);
> > -    int smt_threads = ppc_get_compat_smt_threads(cpu);
> > +    int smt_threads = CPU_CORE(pc)->nr_threads;
> 
> ppc_get_compat_smt_threads() also checks kvmppc_smt_threads() ... as
> long as we do not run the powernv architecture with KVM PR, your change
> should be OK, but if we support that one day, we might need to check
> kvmppc_smt_threads() here, too?

No, actually.  I covered this when I posted this patch standalone
earlier, but forgot to add it to the commit message.  If nr_threads
exceeds kvmppc_smt_threads() then things are already broken, and
clamping the value here isn't going to save us.

> 
> >      CPUPPCState *env = &cpu->env;
> >      PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cs);
> >      uint32_t servers_prop[smt_threads];
> > @@ -206,10 +206,6 @@ static void powernv_create_core_node(PnvChip *chip, PnvCore *pc, void *fdt)
> >      _FDT((fdt_setprop(fdt, offset, "ibm,pa-features",
> >                         pa_features, sizeof(pa_features))));
> >  
> > -    if (cpu->cpu_version) {
> > -        _FDT((fdt_setprop_cell(fdt, offset, "cpu-version", cpu->cpu_version)));
> > -    }
> > -
> >      /* Build interrupt servers properties */
> >      for (i = 0; i < smt_threads; i++) {
> >          servers_prop[i] = cpu_to_be32(pc->pir + i);
> > 
> 
> Reviewed-by: Thomas Huth <thuth@redhat.com>
> 

-- 
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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