[Qemu-devel] s390: Fix cpu shutdown for KVM

[Christian Borntraeger <borntraeger@de.ibm.com>]

qemu/kvm on s390 currently hangs on panic (doesnt exit on disabled
wait) and also shuts down on cpu hot-unplug (SIGP stop).
This patch tries to fix these simple cases.
On s390 a shutdown is the state of all CPUs being either stopped
or disabled (for interrupts) waiting. We have to track this number
to call the shutdown sequence accordingly. This patch implements
the counting and shutdown handling for the kvm path in qemu.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
---
 hw/s390-virtio.c   |    4 ++++
 target-s390x/kvm.c |   29 +++++++++++++++++++++++++----
 2 files changed, 29 insertions(+), 4 deletions(-)

Index: b/hw/s390-virtio.c
===================================================================
--- a/hw/s390-virtio.c
+++ b/hw/s390-virtio.c
@@ -130,6 +130,9 @@ int s390_virtio_hypercall(CPUState *env,
     return r;
 }
 
+/* defined in target-s390x/kvm.c */
+extern int s390_running_cpus;
+
 /* PC hardware initialisation */
 static void s390_init(ram_addr_t my_ram_size,
                       const char *boot_device,
@@ -189,6 +192,7 @@ static void s390_init(ram_addr_t my_ram_
 
     env->halted = 0;
     env->exception_index = 0;
+    s390_running_cpus = 1;
 
     if (kernel_filename) {
         kernel_size = load_image(kernel_filename, qemu_get_ram_ptr(0));
Index: b/target-s390x/kvm.c
===================================================================
--- a/target-s390x/kvm.c
+++ b/target-s390x/kvm.c
@@ -63,6 +63,14 @@
 #define SCLP_CMDW_READ_SCP_INFO         0x00020001
 #define SCLP_CMDW_READ_SCP_INFO_FORCED  0x00120001
 
+/*
+ * The number of running CPUs. On s390 a shutdown is the state of all CPUs
+ * being either stopped or disabled (for interrupts) waiting. We have to
+ * track this number to call the shutdown sequence accordingly. This
+ * number is modified either on startup or while holding the big qemu lock.
+ */
+int s390_running_cpus;
+
 const KVMCapabilityInfo kvm_arch_required_capabilities[] = {
     KVM_CAP_LAST_INFO
 };
@@ -185,6 +193,12 @@ void kvm_s390_interrupt_internal(CPUStat
         return;
     }
 
+    /*
+     * We can only deliver interrupts to (interrupt) enabled CPUs.
+     * We dont modify s390_running_cpus here, since CPUs in enabled wait
+     * will wait inside the kernel (no exit). Therefore, the targeted
+     * CPUs was neither disabled waiting or stopped for qemu.
+     */
     env->halted = 0;
     env->exception_index = -1;
     qemu_cpu_kick(env);
@@ -301,6 +315,7 @@ static int s390_cpu_restart(CPUState *en
     kvm_s390_interrupt(env, KVM_S390_RESTART, 0);
     env->halted = 0;
     env->exception_index = -1;
+    s390_running_cpus++;
     qemu_cpu_kick(env);
     dprintf("DONE: SIGP cpu restart: %p\n", env);
     return 0;
@@ -425,16 +440,24 @@ static int handle_intercept(CPUState *en
             r = handle_instruction(env, run);
             break;
         case ICPT_WAITPSW:
-            /* XXX What to do on system shutdown? */
+            if (--s390_running_cpus == 0) {
+                qemu_system_shutdown_request();
+            }
             env->halted = 1;
             env->exception_index = EXCP_HLT;
+            r = EXCP_HALTED;
             break;
         case ICPT_SOFT_INTERCEPT:
             fprintf(stderr, "KVM unimplemented icpt SOFT\n");
             exit(1);
             break;
         case ICPT_CPU_STOP:
-            qemu_system_shutdown_request();
+            if (--s390_running_cpus == 0) {
+                qemu_system_shutdown_request();
+            }
+            env->halted = 1;
+            env->exception_index = EXCP_HLT;
+            r = EXCP_HALTED;
             break;
         case ICPT_IO:
             fprintf(stderr, "KVM unimplemented icpt IO\n");
@@ -468,8 +491,6 @@ int kvm_arch_handle_exit(CPUState *env, 
 
     if (ret == 0) {
         ret = EXCP_INTERRUPT;
-    } else if (ret > 0) {
-        ret = 0;
     }
     return ret;
 }