Re: [Qemu-devel] [Qemu-ppc] [RFC 1/2] pseries: Split CAS PVR negotiation out into a separate function

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, May 17, 2017 at 05:56:57PM +0200, Greg Kurz wrote:
> On Wed, 17 May 2017 16:35:46 +1000
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > Guests of the qemu machine type go through a feature negotiation process
> > known as "client architecture support" (CAS) during early boot.  This does
> > a number of things, one of which is finding a CPU compatibility mode which
> > can be supported by both guest and host.
> > 
> > In fact the CPU negotiation is probably the single most complex part of the
> > CAS process, so this splits it out into a helper function.  We've recently
> > made some mistakes in maintaining backward compatibility for old machine
> > types here.  Splitting this out will also make it easier to fix this.
> > 
> > This also adds a possibly useful error message if the negotiation fails
> > (i.e. if there is CPU mode that's suitable for both guest and host).
> 
> s/if there is/if there isn't a/ ?

Oops, I'll correct that.

> 
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  hw/ppc/spapr_hcall.c | 43 +++++++++++++++++++++++++++----------------
> >  1 file changed, 27 insertions(+), 16 deletions(-)
> > 
> > diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> > index 0d608d6..007ae8d 100644
> > --- a/hw/ppc/spapr_hcall.c
> > +++ b/hw/ppc/spapr_hcall.c
> > @@ -1047,19 +1047,13 @@ static target_ulong h_signal_sys_reset(PowerPCCPU *cpu,
> >      }
> >  }
> >  
> > -static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
> > -                                                  sPAPRMachineState *spapr,
> > -                                                  target_ulong opcode,
> > -                                                  target_ulong *args)
> > +static uint32_t cas_check_pvr(PowerPCCPU *cpu, target_ulong list,
> > +                              Error **errp)
> >  {
> > -    target_ulong list = ppc64_phys_to_real(args[0]);
> > -    target_ulong ov_table;
> >      bool explicit_match = false; /* Matched the CPU's real PVR */
> >      uint32_t max_compat = cpu->max_compat;
> >      uint32_t best_compat = 0;
> >      int i;
> > -    sPAPROptionVector *ov1_guest, *ov5_guest, *ov5_cas_old, *ov5_updates;
> > -    bool guest_radix;
> >  
> >      /*
> >       * We scan the supplied table of PVRs looking for two things
> > @@ -1090,26 +1084,43 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
> >          /* We couldn't find a suitable compatibility mode, and either
> >           * the guest doesn't support "raw" mode for this CPU, or raw
> >           * mode is disabled because a maximum compat mode is set */
> > -        return H_HARDWARE;
> > +        error_setg(errp, "Couldn't negotiate a suitable PVR during CAS");
> > +        return 0;
> >      }
> >  
> >      /* Parsing finished */
> >      trace_spapr_cas_pvr(cpu->compat_pvr, explicit_match, best_compat);
> >  
> > -    /* Update CPUs */
> > -    if (cpu->compat_pvr != best_compat) {
> > -        Error *local_err = NULL;
> > +    return best_compat;
> > +}
> > +
> > +static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
> > +                                                  sPAPRMachineState *spapr,
> > +                                                  target_ulong opcode,
> > +                                                  target_ulong *args)
> > +{
> > +    /* @ov_table points to the first option vector */
> > +    target_ulong ov_table = ppc64_phys_to_real(args[0]);
> > +    uint32_t cas_pvr;
> > +    sPAPROptionVector *ov1_guest, *ov5_guest, *ov5_cas_old, *ov5_updates;
> > +    bool guest_radix;
> > +    Error *local_err = NULL;
> >  
> > -        ppc_set_compat_all(best_compat, &local_err);
> > +    cas_pvr = cas_check_pvr(cpu, ov_table, &local_err);
> 
> Shouldn't cas_check_pvr() take a target_ulong * so that we can get
> the address of the first option vector...
> 
> > +    if (local_err) {
> > +        error_report_err(local_err);
> > +        return H_HARDWARE;
> > +    }
> > +
> > +    /* Update CPUs */
> > +    if (cpu->compat_pvr != cas_pvr) {
> > +        ppc_set_compat_all(cas_pvr, &local_err);
> >          if (local_err) {
> >              error_report_err(local_err);
> >              return H_HARDWARE;
> >          }
> >      }
> >  
> > -    /* For the future use: here @ov_table points to the first option vector */
> > -    ov_table = list;
> > -
> 
> ... and address Laurent's comment ?

Yes, I completely misread what was happening with the pvr_list vs. the
option vectors.  I'll correct that.

> 
> >      ov1_guest = spapr_ovec_parse_vector(ov_table, 1);
> >      ov5_guest = spapr_ovec_parse_vector(ov_table, 5);
> >      if (spapr_ovec_test(ov5_guest, OV5_MMU_BOTH)) {
> 



-- 
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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