1 files changed, 57 insertions, 8 deletions

diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index dd51adac05..d62fd5fdc6 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -976,6 +976,10 @@ static void arm_cpu_initfn(Object *obj)
     }
 }
 
+static Property arm_cpu_gt_cntfrq_property =
+            DEFINE_PROP_UINT64("cntfrq", ARMCPU, gt_cntfrq_hz,
+                               NANOSECONDS_PER_SECOND / GTIMER_SCALE);
+
 static Property arm_cpu_reset_cbar_property =
             DEFINE_PROP_UINT64("reset-cbar", ARMCPU, reset_cbar, 0);
 
@@ -1055,6 +1059,30 @@ static void arm_set_init_svtor(Object *obj, Visitor *v, const char *name,
     visit_type_uint32(v, name, &cpu->init_svtor, errp);
 }
 
+unsigned int gt_cntfrq_period_ns(ARMCPU *cpu)
+{
+    /*
+     * The exact approach to calculating guest ticks is:
+     *
+     *     muldiv64(qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL), cpu->gt_cntfrq_hz,
+     *              NANOSECONDS_PER_SECOND);
+     *
+     * We don't do that. Rather we intentionally use integer division
+     * truncation below and in the caller for the conversion of host monotonic
+     * time to guest ticks to provide the exact inverse for the semantics of
+     * the QEMUTimer scale factor. QEMUTimer's scale facter is an integer, so
+     * it loses precision when representing frequencies where
+     * `(NANOSECONDS_PER_SECOND % cpu->gt_cntfrq) > 0` holds. Failing to
+     * provide an exact inverse leads to scheduling timers with negative
+     * periods, which in turn leads to sticky behaviour in the guest.
+     *
+     * Finally, CNTFRQ is effectively capped at 1GHz to ensure our scale factor
+     * cannot become zero.
+     */
+    return NANOSECONDS_PER_SECOND > cpu->gt_cntfrq_hz ?
+      NANOSECONDS_PER_SECOND / cpu->gt_cntfrq_hz : 1;
+}
+
 void arm_cpu_post_init(Object *obj)
 {
     ARMCPU *cpu = ARM_CPU(obj);
@@ -1172,6 +1200,11 @@ void arm_cpu_post_init(Object *obj)
 
     qdev_property_add_static(DEVICE(obj), &arm_cpu_cfgend_property,
                              &error_abort);
+
+    if (arm_feature(&cpu->env, ARM_FEATURE_GENERIC_TIMER)) {
+        qdev_property_add_static(DEVICE(cpu), &arm_cpu_gt_cntfrq_property,
+                                 &error_abort);
+    }
 }
 
 static void arm_cpu_finalizefn(Object *obj)
@@ -1251,14 +1284,30 @@ static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
         }
     }
 
-    cpu->gt_timer[GTIMER_PHYS] = timer_new(QEMU_CLOCK_VIRTUAL, GTIMER_SCALE,
-                                           arm_gt_ptimer_cb, cpu);
-    cpu->gt_timer[GTIMER_VIRT] = timer_new(QEMU_CLOCK_VIRTUAL, GTIMER_SCALE,
-                                           arm_gt_vtimer_cb, cpu);
-    cpu->gt_timer[GTIMER_HYP] = timer_new(QEMU_CLOCK_VIRTUAL, GTIMER_SCALE,
-                                          arm_gt_htimer_cb, cpu);
-    cpu->gt_timer[GTIMER_SEC] = timer_new(QEMU_CLOCK_VIRTUAL, GTIMER_SCALE,
-                                          arm_gt_stimer_cb, cpu);
+
+    {
+        uint64_t scale;
+
+        if (arm_feature(env, ARM_FEATURE_GENERIC_TIMER)) {
+            if (!cpu->gt_cntfrq_hz) {
+                error_setg(errp, "Invalid CNTFRQ: %"PRId64"Hz",
+                           cpu->gt_cntfrq_hz);
+                return;
+            }
+            scale = gt_cntfrq_period_ns(cpu);
+        } else {
+            scale = GTIMER_SCALE;
+        }
+
+        cpu->gt_timer[GTIMER_PHYS] = timer_new(QEMU_CLOCK_VIRTUAL, scale,
+                                               arm_gt_ptimer_cb, cpu);
+        cpu->gt_timer[GTIMER_VIRT] = timer_new(QEMU_CLOCK_VIRTUAL, scale,
+                                               arm_gt_vtimer_cb, cpu);
+        cpu->gt_timer[GTIMER_HYP] = timer_new(QEMU_CLOCK_VIRTUAL, scale,
+                                              arm_gt_htimer_cb, cpu);
+        cpu->gt_timer[GTIMER_SEC] = timer_new(QEMU_CLOCK_VIRTUAL, scale,
+                                              arm_gt_stimer_cb, cpu);
+    }
 #endif
 
     cpu_exec_realizefn(cs, &local_err);