PPC/KVM: early validation of vcpu id

The KVM API restricts vcpu ids to be < KVM_CAP_MAX_VCPUS. On PowerPC
targets, depending on the number of threads per core in the host and
in the guest, some topologies do generate higher vcpu ids actually.
When this happens, QEMU bails out with the following error:

kvm_init_vcpu failed: Invalid argument

The KVM_CREATE_VCPU ioctl has several EINVAL return paths, so it is
not possible to fully disambiguate.

This patch adds a check in the code that computes vcpu ids, so that
we can detect the error earlier, and print a friendlier message instead
of calling KVM_CREATE_VCPU with an obviously bogus vcpu id.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
index f9f00e2e56cba881678644f5485b405c1087990f..f357ccde91223c49a9f9eaf459cf558045e7287a 100644 (file)
--- a/include/sysemu/kvm.h
+++ b/include/sysemu/kvm.h
@@ -345,6 +345,8 @@ int kvm_arch_init(MachineState *ms, KVMState *s);
 
 int kvm_arch_init_vcpu(CPUState *cpu);
 
+bool kvm_vcpu_id_is_valid(int vcpu_id);
+
 /* Returns VCPU ID to be used on KVM_CREATE_VCPU ioctl() */
 unsigned long kvm_arch_vcpu_id(CPUState *cpu);
 

diff --git a/kvm-all.c b/kvm-all.c
index f9ae8f9bf809c891d873c863dd5c2b06b7ab56ec..e56f385278156426a9ae1b76b6c8ee02089a08a6 100644 (file)
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -1459,6 +1459,12 @@ static int kvm_max_vcpus(KVMState *s)
     return (ret) ? ret : kvm_recommended_vcpus(s);
 }
 
+bool kvm_vcpu_id_is_valid(int vcpu_id)
+{
+    KVMState *s = KVM_STATE(current_machine->accelerator);
+    return vcpu_id >= 0 && vcpu_id < kvm_max_vcpus(s);
+}
+
 static int kvm_init(MachineState *ms)
 {
     MachineClass *mc = MACHINE_GET_CLASS(ms);

diff --git a/target-ppc/translate_init.c b/target-ppc/translate_init.c
index 954195f5e494701df66d5eb1860cc7363d3d14fa..a003c1029d31cd119dd652889922222c7c002788 100644 (file)
--- a/target-ppc/translate_init.c
+++ b/target-ppc/translate_init.c
@@ -9231,6 +9231,14 @@ static void ppc_cpu_realizefn(DeviceState *dev, Error **errp)
 #if !defined(CONFIG_USER_ONLY)
     cpu->cpu_dt_id = (cs->cpu_index / smp_threads) * max_smt
         + (cs->cpu_index % smp_threads);
+
+    if (kvm_enabled() && !kvm_vcpu_id_is_valid(cpu->cpu_dt_id)) {
+        error_setg(errp, "Can't create CPU with id %d in KVM", cpu->cpu_dt_id);
+        error_append_hint(errp, "Adjust the number of cpus to %d "
+                          "or try to raise the number of threads per core\n",
+                          cpu->cpu_dt_id * smp_threads / max_smt);
+        return;
+    }
 #endif
 
     if (tcg_enabled()) {