Philippe Mathieu-Daudé <phi...@redhat.com> writes:
> On 7/22/20 5:50 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 | 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); > > Since here object_new() is used, it is simpler to set the field before > the object is realized, similarly to cs->cpu_index: > > -- >8 -- > @@ -275,6 +275,11 @@ static PowerPCCPU *spapr_create_vcpu(SpaprCpuCore > *sc, int i, Error **errp) > cs = CPU(obj); > cpu = POWERPC_CPU(obj); > cs->cpu_index = cc->core_id + i; > + /* > + * 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; > spapr_set_vcpu_id(cpu, cs->cpu_index, &local_err); > if (local_err) { > goto err; > --- Good point. I adopted your suggestion. -- Thiago Jung Bauermann IBM Linux Technology Center