On Mon, 08 Jun 2020 15:18:50 -0500 Babu Moger <babu.mo...@amd.com> wrote:
> Noticed the following command failure while testing CPU hotplug. > > $ qemu-system-x86_64 -machine q35,accel=kvm -smp 1,maxcpus=2, > cores=1, threads=1,sockets=2 -cpu EPYC -device EPYC-x86_64- > cpu,core-id=0,socket-id=1,thread-id=0 > > qemu-system-x86_64: -device EPYC-x86_64-cpu,core-id=0,socket-id=1, > thread-id=0: Invalid CPU [socket: 21855, die: 0, core: 0, thread: 0] > with APIC ID 21855, valid index range 0:1 > > This happens because APIC ID is calculated using uninitialized memory. > This is happening after the addition of new field node_id in X86CPUTopoIDs > structure. The node_id field is uninitialized while calling > apicid_from_topo_ids. The problem is discussed in the thread below. > https://lore.kernel.org/qemu-devel/20200602171838.gg577...@habkost.net/ > > Fix the problem by initializing the node_id properly. > > Signed-off-by: Babu Moger <babu.mo...@amd.com> > --- > hw/i386/pc.c | 2 ++ > include/hw/i386/topology.h | 11 +++++++++++ > 2 files changed, 13 insertions(+) > > diff --git a/hw/i386/pc.c b/hw/i386/pc.c > index 2128f3d6fe..974cc30891 100644 > --- a/hw/i386/pc.c > +++ b/hw/i386/pc.c > @@ -1585,6 +1585,8 @@ static void pc_cpu_pre_plug(HotplugHandler *hotplug_dev, > topo_ids.die_id = cpu->die_id; > topo_ids.core_id = cpu->core_id; > topo_ids.smt_id = cpu->thread_id; > + topo_ids.node_id = cpu_x86_use_epyc_apic_id_encoding(ms->cpu_type) ? > + x86_node_id_for_epyc(&topo_info, &topo_ids) : 0; I'd rather not calculate some default value here, this is the branch where we check user provided topology info and error out asking to provide missing bits. I also wonder if we should force user to specify numa nodes on CLI if EPYC cpu is used. (i.e. I'm assuming that EPYC always requires numa) > cpu->apic_id = x86ms->apicid_from_topo_ids(&topo_info, &topo_ids); > } > > diff --git a/include/hw/i386/topology.h b/include/hw/i386/topology.h > index 07239f95f4..ee4deb84c4 100644 > --- a/include/hw/i386/topology.h > +++ b/include/hw/i386/topology.h > @@ -140,6 +140,17 @@ static inline unsigned > apicid_pkg_offset_epyc(X86CPUTopoInfo *topo_info) > apicid_node_width_epyc(topo_info); > } > > +static inline unsigned x86_node_id_for_epyc(X86CPUTopoInfo *topo_info, > + const X86CPUTopoIDs *topo_ids) > +{ > + unsigned nr_nodes = MAX(topo_info->nodes_per_pkg, 1); > + unsigned cores_per_node = DIV_ROUND_UP((topo_info->dies_per_pkg * > + topo_info->cores_per_die * > + topo_info->threads_per_core), > + nr_nodes); > + > + return (topo_ids->core_id / cores_per_node) % nr_nodes; what if nr_nodes == 0? > +} > /* > * Make APIC ID for the CPU based on Pkg_ID, Core_ID, SMT_ID > * > >
