After reset, both TOD and CKC values are set to 0, so if
clock-comparator interrupts are enabled, one should occur shortly
thereafter.

Currently the code does not set tod_timer, so this does not happen.

Fix by adding a tcg_s390_tod_updated() call. Initialize TOD clock
before CPUs in order to ensure that the respective object exists
during the CPU reset.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 hw/s390x/s390-virtio-ccw.c | 6 +++---
 target/s390x/cpu.c         | 8 ++++++++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
index ad2c48188a8..9f37a96ae5a 100644
--- a/hw/s390x/s390-virtio-ccw.c
+++ b/hw/s390x/s390-virtio-ccw.c
@@ -286,6 +286,9 @@ static void ccw_init(MachineState *machine)
     /* init memory + setup max page size. Required for the CPU model */
     s390_memory_init(machine);
 
+    /* init the TOD clock */
+    s390_init_tod();
+
     /* init CPUs (incl. CPU model) early so s390_has_feature() works */
     s390_init_cpus(machine);
 
@@ -332,9 +335,6 @@ static void ccw_init(MachineState *machine)
         s390_create_sclpconsole(ms->sclp, "sclplmconsole", serial_hd(1));
     }
 
-    /* init the TOD clock */
-    s390_init_tod();
-
     /* init SCLP event Control-Program Identification */
     if (s390mc->use_cpi) {
         s390_create_sclpcpi(ms->sclp);
diff --git a/target/s390x/cpu.c b/target/s390x/cpu.c
index f05ce317da1..cc2de6ce08e 100644
--- a/target/s390x/cpu.c
+++ b/target/s390x/cpu.c
@@ -40,6 +40,7 @@
 #include "system/reset.h"
 #endif
 #include "hw/s390x/cpu-topology.h"
+#include "tcg/tcg_s390x.h"
 
 #define CR0_RESET       0xE0UL
 #define CR14_RESET      0xC2000000UL;
@@ -215,6 +216,13 @@ static void s390_cpu_reset_hold(Object *obj, ResetType type)
             break;
         }
     }
+
+#ifndef CONFIG_USER_ONLY
+    if (tcg_enabled()) {
+        /* Rearm the CKC timer if necessary */
+        tcg_s390_tod_updated(CPU(cpu), RUN_ON_CPU_NULL);
+    }
+#endif
 }
 
 static void s390_cpu_disas_set_info(CPUState *cpu, disassemble_info *info)
-- 
2.51.0

On Tue, 2025-10-14 at 18:05 +0200, Ilya Leoshkevich wrote:
> After reset, both TOD and CKC values are set to 0, so if
                    ^^^

This is inaccurate, only the TOD programmable register is set to 0.
I will fix this in v2.

> clock-comparator interrupts are enabled, one should occur shortly
> thereafter.
> 
> Currently the code does not set tod_timer, so this does not happen.
> 
> Fix by adding a tcg_s390_tod_updated() call. Initialize TOD clock
> before CPUs in order to ensure that the respective object exists
> during the CPU reset.
> 
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>  hw/s390x/s390-virtio-ccw.c | 6 +++---
>  target/s390x/cpu.c         | 8 ++++++++
>  2 files changed, 11 insertions(+), 3 deletions(-)

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