[PATCH v2 14/16] target/ppc: PMU: insns counter negative overflow support

[Daniel Henrique Barboza <danielhb413@gmail.com>]

Enabling counter negative overflow for the PMCs that are counting
instructions is simpler than when counting cycles. Instruction
counting is done via helper_insns_inc(), which is called every
time a TB ends.

Firing a performance monitor alert due to a counter negative overflow
in this case is a matter of checking if the counter value is over
0x80000000 each time the counters are incremented and, if counter negative
events are enabled for that specific counter, trigger the PM alert.

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
---
 target/ppc/power8_pmu.c | 23 +++++++++++++++++++++--
 target/ppc/translate.c  |  8 ++++++++
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/target/ppc/power8_pmu.c b/target/ppc/power8_pmu.c
index 690476051d..28db086225 100644
--- a/target/ppc/power8_pmu.c
+++ b/target/ppc/power8_pmu.c
@@ -252,9 +252,8 @@ static void start_cycle_count_session(CPUPPCState *env)
     }
 }
 
-static void cpu_ppc_pmu_timer_cb(void *opaque)
+static void fire_PMC_interrupt(PowerPCCPU *cpu)
 {
-    PowerPCCPU *cpu = opaque;
     CPUPPCState *env = &cpu->env;
 
     if (!(env->spr[SPR_POWER_MMCR0] & MMCR0_EBE)) {
@@ -284,6 +283,13 @@ static void cpu_ppc_pmu_timer_cb(void *opaque)
     ppc_set_irq(cpu, PPC_INTERRUPT_PMC, 1);
 }
 
+static void cpu_ppc_pmu_timer_cb(void *opaque)
+{
+    PowerPCCPU *cpu = opaque;
+
+    fire_PMC_interrupt(cpu);
+}
+
 void cpu_ppc_pmu_timer_init(CPUPPCState *env)
 {
     PowerPCCPU *cpu = env_archcpu(env);
@@ -377,6 +383,8 @@ static bool pmc_counting_insns(CPUPPCState *env, int sprn,
 /* This helper assumes that the PMC is running. */
 void helper_insns_inc(CPUPPCState *env, uint32_t num_insns)
 {
+    bool overflow_triggered = false;
+    PowerPCCPU *cpu;
     int sprn;
 
     for (sprn = SPR_POWER_PMC1; sprn <= SPR_POWER_PMC5; sprn++) {
@@ -390,8 +398,19 @@ void helper_insns_inc(CPUPPCState *env, uint32_t num_insns)
             } else {
                 env->spr[sprn] += num_insns;
             }
+
+            if (env->spr[sprn] >= COUNTER_NEGATIVE_VAL &&
+                pmc_counter_negative_enabled(env, sprn)) {
+                overflow_triggered = true;
+                env->spr[sprn] = COUNTER_NEGATIVE_VAL;
+            }
         }
     }
+
+    if (overflow_triggered) {
+        cpu = env_archcpu(env);
+        fire_PMC_interrupt(cpu);
+    }
 }
 
 #endif /* defined(TARGET_PPC64) && !defined(CONFIG_USER_ONLY) */
diff --git a/target/ppc/translate.c b/target/ppc/translate.c
index d4cfc567cf..8302022852 100644
--- a/target/ppc/translate.c
+++ b/target/ppc/translate.c
@@ -4437,6 +4437,14 @@ static void pmu_count_insns(DisasContext *ctx)
     tcg_gen_andi_tl(t0, t0, MMCR0_FC);
     tcg_gen_brcond_tl(TCG_COND_EQ, t0, t_mmcr0FC, l_exit);
 
+    /*
+     * The PMU insns_inc() helper stops the internal PMU timer if a
+     * counter overflows happens. In that case, if the guest is
+     * running with icount and we do not handle it beforehand,
+     * the helper can trigger a 'bad icount read'.
+     */
+    gen_icount_io_start(ctx);
+
     gen_helper_insns_inc(cpu_env, tcg_constant_i32(ctx->base.num_insns));
 
     gen_set_label(l_exit);
-- 
2.31.1