Re: [PATCH] ppc/spapr: Add ibm,pi-features

[Harsh Prateek Bora <harshpb@linux.ibm.com>]

On 5/18/24 15:26, Nicholas Piggin wrote:
> The ibm,pi-features property has a bit to say whether or not
> msgsndp should be used. Linux checks if it is being run under
> KVM and avoids msgsndp anyway, but it would be preferable to
> rely on this bit.
> 
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>

> ---
>   hw/ppc/spapr.c | 27 +++++++++++++++++++++++++++
>   1 file changed, 27 insertions(+)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 611a9e5184..6891d91e6e 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -353,6 +353,31 @@ static void spapr_dt_pa_features(SpaprMachineState *spapr,
>       _FDT((fdt_setprop(fdt, offset, "ibm,pa-features", pa_features, pa_size)));
>   }
>   
> +static void spapr_dt_pi_features(SpaprMachineState *spapr,
> +                                 PowerPCCPU *cpu,
> +                                 void *fdt, int offset)
> +{
> +    uint8_t pi_features[] = { 1, 0,
> +        0x00 };
> +
> +    if (kvm_enabled() && ppc_check_compat(cpu, CPU_POWERPC_LOGICAL_3_00,
> +                                          0, cpu->compat_pvr)) {
> +        /*
> +         * POWER9 and later CPUs with KVM run in LPAR-per-thread mode where
> +         * all threads are essentially independent CPUs, and msgsndp does not
> +         * work (because it is physically-addressed) and therefore is
> +         * emulated by KVM, so disable it here to ensure XIVE will be used.
> +         * This is both KVM and CPU implementation-specific behaviour so a KVM
> +         * cap would be cleanest, but for now this works. If KVM ever permits
> +         * native msgsndp execution by guests, a cap could be added at that
> +         * time.
> +         */
> +        pi_features[2] |= 0x08; /* 4: No msgsndp */
> +    }
> +
> +    _FDT((fdt_setprop(fdt, offset, "ibm,pi-features", pi_features, sizeof(pi_features))));
> +}
> +
>   static hwaddr spapr_node0_size(MachineState *machine)
>   {
>       if (machine->numa_state->num_nodes) {
> @@ -815,6 +840,8 @@ static void spapr_dt_cpu(CPUState *cs, void *fdt, int offset,
>   
>       spapr_dt_pa_features(spapr, cpu, fdt, offset);
>   
> +    spapr_dt_pi_features(spapr, cpu, fdt, offset);
> +
>       _FDT((fdt_setprop_cell(fdt, offset, "ibm,chip-id",
>                              cs->cpu_index / vcpus_per_socket)));
>