On 7/23/20 4:56 AM, Thiago Jung Bauermann wrote: > 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 | 10 +++++----- > 1 file changed, 5 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..2125fdac34 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]; > @@ -274,6 +269,11 @@ static PowerPCCPU *spapr_create_vcpu(SpaprCpuCore *sc, > int i, Error **errp) > > cs = CPU(obj); > cpu = POWERPC_CPU(obj); > + /* > + * 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->start_powered_off = true; > cs->cpu_index = cc->core_id + i; > spapr_set_vcpu_id(cpu, cs->cpu_index, &local_err); > if (local_err) { >
Reviewed-by: Philippe Mathieu-Daudé <phi...@redhat.com>