[PULL,25/30] spapr: TCG allow up to 8-thread SMT on POWER8 and newer CPUs

Commit Message

Cédric Le Goater June 26, 2023, 5:56 a.m. UTC

From: Nicholas Piggin <[e-mail]>

PPC TCG supports SMT CPU configurations for non-hypervisor state, so
permit POWER8-10 pseries machines to enable SMT.

This requires PIR and TIR be set, because that's how sibling thread
matching is done by TCG.

spapr's nested-HV capability does not currently coexist with SMT, so
that combination is prohibited (interestingly somewhat analogous to
LPAR-per-core mode on real hardware which also does not support KVM).

Signed-off-by: Nicholas Piggin <[e-mail]>
Reviewed-by: Cédric Le Goater <[e-mail]>
[ clg: Also test smp_threads when checking for POWER8 CPU and above ]
Signed-off-by: Cédric Le Goater <[e-mail]>
---
 hw/ppc/spapr.c          | 17 +++++++++++++----
 hw/ppc/spapr_caps.c     | 14 ++++++++++++++
 hw/ppc/spapr_cpu_core.c |  7 +++++--
 3 files changed, 32 insertions(+), 6 deletions(-)

Patch

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 8e7d497f25fa..54dbfd7fe983 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -2525,10 +2525,19 @@  static void spapr_set_vsmt_mode(SpaprMachineState *spapr, Error **errp)
     int ret;
     unsigned int smp_threads = ms->smp.threads;
 
-    if (tcg_enabled() && (smp_threads > 1)) {
-        error_setg(errp, "TCG cannot support more than 1 thread/core "
-                   "on a pseries machine");
-        return;
+    if (tcg_enabled()) {
+        if (smp_threads > 1 &&
+            !ppc_type_check_compat(ms->cpu_type, CPU_POWERPC_LOGICAL_2_07, 0,
+                                   spapr->max_compat_pvr)) {
+            error_setg(errp, "TCG only supports SMT on POWER8 or newer CPUs");
+            return;
+        }
+
+        if (smp_threads > 8) {
+            error_setg(errp, "TCG cannot support more than 8 threads/core "
+                       "on a pseries machine");
+            return;
+        }
     }
     if (!is_power_of_2(smp_threads)) {
         error_setg(errp, "Cannot support %d threads/core on a pseries "
diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
index 3fd45a6decc2..5a0755d34fbe 100644
--- a/hw/ppc/spapr_caps.c
+++ b/hw/ppc/spapr_caps.c
@@ -473,6 +473,20 @@  static void cap_nested_kvm_hv_apply(SpaprMachineState *spapr,
                 error_append_hint(errp,
                                   "Try appending -machine cap-nested-hv=off\n");
         }
+    } else if (tcg_enabled()) {
+        MachineState *ms = MACHINE(spapr);
+        unsigned int smp_threads = ms->smp.threads;
+
+        /*
+         * Nested-HV vCPU env state to L2, so SMT-shared SPR updates, for
+         * example, do not necessarily update the correct SPR value on sibling
+         * threads that are in a different guest/host context.
+         */
+        if (smp_threads > 1) {
+            error_setg(errp, "TCG does not support nested-HV with SMT");
+            error_append_hint(errp, "Try appending -machine cap-nested-hv=off "
+                                    "or use threads=1 with -smp\n");
+        }
     }
 }
 
diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
index 9b88dd549a6c..a4e3c2fadd60 100644
--- a/hw/ppc/spapr_cpu_core.c
+++ b/hw/ppc/spapr_cpu_core.c
@@ -255,7 +255,7 @@  static void spapr_cpu_core_unrealize(DeviceState *dev)
 }
 
 static bool spapr_realize_vcpu(PowerPCCPU *cpu, SpaprMachineState *spapr,
-                               SpaprCpuCore *sc, Error **errp)
+                               SpaprCpuCore *sc, int thread_index, Error **errp)
 {
     CPUPPCState *env = &cpu->env;
     CPUState *cs = CPU(cpu);
@@ -267,6 +267,9 @@  static bool spapr_realize_vcpu(PowerPCCPU *cpu, SpaprMachineState *spapr,
     cpu_ppc_set_vhyp(cpu, PPC_VIRTUAL_HYPERVISOR(spapr));
     kvmppc_set_papr(cpu);
 
+    env->spr_cb[SPR_PIR].default_value = cs->cpu_index;
+    env->spr_cb[SPR_TIR].default_value = thread_index;
+
     /* Set time-base frequency to 512 MHz. vhyp must be set first. */
     cpu_ppc_tb_init(env, SPAPR_TIMEBASE_FREQ);
 
@@ -337,7 +340,7 @@  static void spapr_cpu_core_realize(DeviceState *dev, Error **errp)
     for (i = 0; i < cc->nr_threads; i++) {
         sc->threads[i] = spapr_create_vcpu(sc, i, errp);
         if (!sc->threads[i] ||
-            !spapr_realize_vcpu(sc->threads[i], spapr, sc, errp)) {
+            !spapr_realize_vcpu(sc->threads[i], spapr, sc, i, errp)) {
             spapr_cpu_core_unrealize(dev);
             return;
         }