Re: [Qemu-ppc] [RFC for-2.12 8/8] spapr: Handle Decimal Floating Point (DFP) as an optional capability

[Greg Kurz]

On Mon, 11 Dec 2017 18:08:08 +1100
David Gibson <address@hidden> wrote:

> Decimal Floating Point has been available on POWER7 and later (server)
> cpus.  However, it can be disabled on the hypervisor, meaning that it's
> not available to guests.
> 
> We currently handle this by conditionally advertising DFP support in the
> device tree depending on whether the guest CPU model supports it - which
> can also depend on what's allowed in the host for -cpu host.  That can lead
> to confusion on migration, since host properties are silently affecting
> guest visible properties.
> 
> This patch handles it by treating it as an optional capability for the
> pseries machine type.
> 
> Signed-off-by: David Gibson <address@hidden>
> ---
>  hw/ppc/spapr.c         |  5 +++--
>  hw/ppc/spapr_caps.c    | 17 +++++++++++++++++
>  include/hw/ppc/spapr.h |  3 +++
>  3 files changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 6b37511e8f..cca3789b35 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -571,7 +571,7 @@ static void spapr_populate_cpu_dt(CPUState *cs, void 
> *fdt, int offset,
>      /* Advertise DFP (Decimal Floating Point) if available
>       *   0 / no property == no DFP
>       *   1               == DFP available */
> -    if (env->insns_flags2 & PPC2_DFP) {
> +    if (spapr_has_cap(spapr, SPAPR_CAP_DFP)) {
>          _FDT((fdt_setprop_cell(fdt, offset, "ibm,dfp", 1)));
>      }
>  
> @@ -3831,7 +3831,8 @@ static void spapr_machine_class_init(ObjectClass *oc, 
> void *data)
>       */
>      mc->numa_mem_align_shift = 28;
>  
> -    smc->default_caps = spapr_caps(SPAPR_CAP_HTM | SPAPR_CAP_VSX);
> +    smc->default_caps = spapr_caps(SPAPR_CAP_HTM | SPAPR_CAP_VSX
> +                                   | SPAPR_CAP_DFP);
>      spapr_capability_properties(smc, &error_abort);
>  }
>  
> diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
> index b19a9f4417..49c2e10d27 100644
> --- a/hw/ppc/spapr_caps.c
> +++ b/hw/ppc/spapr_caps.c
> @@ -49,6 +49,11 @@ static sPAPRCapabilityInfo capability_table[] = {
>          .description = "Allow Vector Scalar Extensions (VSX)",
>          .bit = SPAPR_CAP_VSX,
>      },
> +    {
> +        .name = "dfp",
> +        .description = "Allow Decimal Floating Point (DFP)",
> +        .bit = SPAPR_CAP_DFP,
> +    },
>  };
>  
>  static sPAPRCapabilities default_caps_with_cpu(sPAPRMachineState *spapr, 
> CPUState *cs)
> @@ -67,6 +72,7 @@ static sPAPRCapabilities 
> default_caps_with_cpu(sPAPRMachineState *spapr, CPUStat
>      if (!ppc_check_compat(cpu, CPU_POWERPC_LOGICAL_2_06,
>                            0, spapr->max_compat_pvr)) {
>          caps.mask &= ~SPAPR_CAP_VSX;
> +        caps.mask &= ~SPAPR_CAP_DFP;
>      }
>  
>      return caps;
> @@ -184,6 +190,13 @@ static void spapr_allow_caps(sPAPRMachineState *spapr, 
> Error **errp)
>          }
>      }
>  
> +    if (spapr_has_cap(spapr, SPAPR_CAP_DFP)) {
> +        if (!(env->insns_flags2 & PPC2_DFP)) {
> +            error_setg(&err, "DFP support not available, try cap-dfp=off");
> +            goto out;
> +        }
> +    }
> +
>  out:
>      if (err) {
>          error_propagate(errp, err);
> @@ -199,6 +212,10 @@ static void spapr_enforce_caps(sPAPRMachineState *spapr, 
> Error **errp)
>      if (!spapr_has_cap(spapr, SPAPR_CAP_VSX)) {
>          /* TODO: Any way to disable VSX? */
>      }
> +
> +    if (!spapr_has_cap(spapr, SPAPR_CAP_VSX)) {

s/SPAPR_CAP_VSX/SPAPR_CAP_DFP/

With that fixed:

Reviewed-by: Greg Kurz <address@hidden>

> +        /* TODO: Any way to disable DFP? */
> +    }
>  }
>  
>  void spapr_caps_reset(sPAPRMachineState *spapr)
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index 4c173cb40c..ef4f7427de 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -62,6 +62,9 @@ typedef enum {
>  /* Vector Scalar Extensions */
>  #define SPAPR_CAP_VSX               0x0000000000000002ULL
>  
> +/* Decimal Floating Point */
> +#define SPAPR_CAP_DFP               0x0000000000000004ULL
> +
>  typedef struct sPAPRCapabilities sPAPRCapabilities;
>  struct sPAPRCapabilities {
>      uint64_t mask;