Re: [Qemu-devel] [PATCH 1/7] spapr: Simplify handling of pre ISA 3.0 guest workaround handling

["Cédric Le Goater" <clg@kaod.org>]

On 11/09/2019 06:04, David Gibson wrote:
> Certain old guest versions don't understand the radix MMU introduced with
> POWER ISA 3.0, but incorrectly select it if presented with the option at
> CAS time.  We workaround this in qemu by explicitly excluding the radix
> (and other ISA 3.0 linked) options if the guest doesn't explicitly note
> support for ISA 3.0.
> 
> This is handled by the 'cas_legacy_guest_workaround' flag, which is pretty
> vague.  Rename it to 'cas_pre_isa3_guest' to be clearer about what it's for.
> 
> In addition, we unnecessarily call spapr_populate_pa_features() with
> different options when initially constructing the device tree and when
> adjusting it at CAS time.  At the initial construct time cas_pre_isa3_guest
> is already false, so we can still use the flag, rather than explicitly
> overriding it to be false at the callsite.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>


Reviewed-by: Cédric Le Goater <clg@kaod.org>

Thanks,

C.

> ---
>  hw/ppc/spapr.c         | 10 ++++------
>  hw/ppc/spapr_hcall.c   |  3 +--
>  include/hw/ppc/spapr.h |  2 +-
>  3 files changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 7124053b43..c551001f86 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -218,8 +218,7 @@ static int spapr_fixup_cpu_numa_dt(void *fdt, int offset, PowerPCCPU *cpu)
>  /* Populate the "ibm,pa-features" property */
>  static void spapr_populate_pa_features(SpaprMachineState *spapr,
>                                         PowerPCCPU *cpu,
> -                                       void *fdt, int offset,
> -                                       bool legacy_guest)
> +                                       void *fdt, int offset)
>  {
>      uint8_t pa_features_206[] = { 6, 0,
>          0xf6, 0x1f, 0xc7, 0x00, 0x80, 0xc0 };
> @@ -285,7 +284,7 @@ static void spapr_populate_pa_features(SpaprMachineState *spapr,
>      if ((spapr_get_cap(spapr, SPAPR_CAP_HTM) != 0) && pa_size > 24) {
>          pa_features[24] |= 0x80;    /* Transactional memory support */
>      }
> -    if (legacy_guest && pa_size > 40) {
> +    if (spapr->cas_pre_isa3_guest && pa_size > 40) {
>          /* Workaround for broken kernels that attempt (guest) radix
>           * mode when they can't handle it, if they see the radix bit set
>           * in pa-features. So hide it from them. */
> @@ -348,8 +347,7 @@ static int spapr_fixup_cpu_dt(void *fdt, SpaprMachineState *spapr)
>              return ret;
>          }
>  
> -        spapr_populate_pa_features(spapr, cpu, fdt, offset,
> -                                   spapr->cas_legacy_guest_workaround);
> +        spapr_populate_pa_features(spapr, cpu, fdt, offset);
>      }
>      return ret;
>  }
> @@ -551,7 +549,7 @@ static void spapr_populate_cpu_dt(CPUState *cs, void *fdt, int offset,
>                            page_sizes_prop, page_sizes_prop_size)));
>      }
>  
> -    spapr_populate_pa_features(spapr, cpu, fdt, offset, false);
> +    spapr_populate_pa_features(spapr, cpu, fdt, offset);
>  
>      _FDT((fdt_setprop_cell(fdt, offset, "ibm,chip-id",
>                             cs->cpu_index / vcpus_per_socket)));
> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> index 23e4bdb829..3d3a67149a 100644
> --- a/hw/ppc/spapr_hcall.c
> +++ b/hw/ppc/spapr_hcall.c
> @@ -1765,8 +1765,7 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
>              exit(EXIT_FAILURE);
>          }
>      }
> -    spapr->cas_legacy_guest_workaround = !spapr_ovec_test(ov1_guest,
> -                                                          OV1_PPC_3_00);
> +    spapr->cas_pre_isa3_guest = !spapr_ovec_test(ov1_guest, OV1_PPC_3_00);
>      spapr_ovec_cleanup(ov1_guest);
>      if (!spapr->cas_reboot) {
>          /* If spapr_machine_reset() did not set up a HPT but one is necessary
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index 03111fd55b..dfec8e8e76 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -175,7 +175,7 @@ struct SpaprMachineState {
>  
>      /* ibm,client-architecture-support option negotiation */
>      bool cas_reboot;
> -    bool cas_legacy_guest_workaround;
> +    bool cas_pre_isa3_guest;
>      SpaprOptionVector *ov5;         /* QEMU-supported option vectors */
>      SpaprOptionVector *ov5_cas;     /* negotiated (via CAS) option vectors */
>      uint32_t max_compat_pvr;
>