powerpc/spapr: Add host threads parameter to ibm,get_system_parameter

The ibm,get_system_parameter rtas call is used by the guest to retrieve
data relating to certain parameters of the system. The SPLPAR
characteristics option (token 20) is used to determine characteristics of
the environment in which the lpar will run.

It may be useful for a guest to know the number of physical host threads
present on the underlying system where it is being run. Add the
characteristic "HostThrs" to the SPLPAR Characteristics
ibm,get_system_parameter rtas call to expose this information to a
guest. Add a n_host_threads property to the processor class which is
then used to retrieve this information and define it for POWER8 and
POWER9. Other processors will default to 0 and the charateristic won't
be added.

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>

Message-Id: <20190827045751.22123-1-sjitindarsingh@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

1 files changed, 15 insertions, 0 deletions

diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
index 526b489297..bee3835214 100644
--- a/hw/ppc/spapr_rtas.c
+++ b/hw/ppc/spapr_rtas.c
@@ -266,6 +266,7 @@ static void rtas_ibm_get_system_parameter(PowerPCCPU *cpu,
                                           target_ulong args,
                                           uint32_t nret, target_ulong rets)
 {
+    PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);
     MachineState *ms = MACHINE(qdev_get_machine());
     unsigned int max_cpus = ms->smp.max_cpus;
     target_ulong parameter = rtas_ld(args, 0);
@@ -283,6 +284,20 @@ static void rtas_ibm_get_system_parameter(PowerPCCPU *cpu,
                                           current_machine->ram_size / MiB,
                                           ms->smp.cpus,
                                           max_cpus);
+        if (pcc->n_host_threads > 0) {
+            char *hostthr_val, *old = param_val;
+
+            /*
+             * Add HostThrs property. This property is not present in PAPR but
+             * is expected by some guests to communicate the number of physical
+             * host threads per core on the system so that they can scale
+             * information which varies based on the thread configuration.
+             */
+            hostthr_val = g_strdup_printf(",HostThrs=%d", pcc->n_host_threads);
+            param_val = g_strconcat(param_val, hostthr_val, NULL);
+            g_free(hostthr_val);
+            g_free(old);
+        }
         ret = sysparm_st(buffer, length, param_val, strlen(param_val) + 1);
         g_free(param_val);
         break;