PowerPC sPAPR CPUs start in the halted state, and spapr_reset_vcpu() attempts to implement this by setting CPUState::halted to 1. But that's too late for the case of hotplugged CPUs in a machine configure with 2 or more threads per core.
By then, other parts of QEMU have already caused the vCPU to run in an unitialized state a couple of times. For example, ppc_cpu_reset() calls ppc_tlb_invalidate_all(), which ends up calling async_run_on_cpu(). This kicks the new vCPU while it has CPUState::halted = 0, causing QEMU to issue a KVM_RUN ioctl on the new vCPU before the guest is able to make the start-cpu RTAS call to initialize its register state. This problem doesn't seem to cause visible issues for regular guests, but on a secure guest running under the Ultravisor it does. The Ultravisor relies on being able to snoop on the start-cpu RTAS call to map vCPUs to guests, and this issue causes it to see a stray vCPU that doesn't belong to any guest. Fix by setting the start-powered-off CPUState property in spapr_create_vcpu(), which makes cpu_common_reset() initialize CPUState::halted to 1 at an earlier moment. Suggested-by: Eduardo Habkost <ehabk...@redhat.com> Signed-off-by: Thiago Jung Bauermann <bauer...@linux.ibm.com> --- hw/ppc/spapr_cpu_core.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) NB: Tested on ppc64le pseries KVM guest with two threads per core. Hot-plugging additional cores doesn't cause the bug described above anymore. diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c index c4f47dcc04..09feeb5f8f 100644 --- a/hw/ppc/spapr_cpu_core.c +++ b/hw/ppc/spapr_cpu_core.c @@ -36,11 +36,6 @@ static void spapr_reset_vcpu(PowerPCCPU *cpu) cpu_reset(cs); - /* All CPUs start halted. CPU0 is unhalted from the machine level - * reset code and the rest are explicitly started up by the guest - * using an RTAS call */ - cs->halted = 1; - env->spr[SPR_HIOR] = 0; lpcr = env->spr[SPR_LPCR]; @@ -288,6 +283,13 @@ static PowerPCCPU *spapr_create_vcpu(SpaprCpuCore *sc, int i, Error **errp) cpu->machine_data = g_new0(SpaprCpuState, 1); + /* + * All CPUs start halted. CPU0 is unhalted from the machine level reset code + * and the rest are explicitly started up by the guest using an RTAS call. + */ + object_property_set_bool(OBJECT(cs), "start-powered-off", true, + &error_abort); + object_unref(obj); return cpu;