RE: [PATCH v7 07/13] hw/386: Add EPYC mode topology decoding functions

[Babu Moger]

> -----Original Message-----
> From: Eduardo Habkost <ehabkost@redhat.com>
> Sent: Tuesday, June 2, 2020 12:19 PM
> To: Moger, Babu <Babu.Moger@amd.com>
> Cc: marcel.apfelbaum@gmail.com; pbonzini@redhat.com; rth@twiddle.net;
> mst@redhat.com; imammedo@redhat.com; qemu-devel@nongnu.org
> Subject: Re: [PATCH v7 07/13] hw/386: Add EPYC mode topology decoding
> functions
> 
> Hi,
> 
> It looks like this series breaks -device and CPU hotplug:
> 
> On Wed, Mar 11, 2020 at 05:53:34PM -0500, Babu Moger wrote:
> > These functions add support for building EPYC mode topology given the smp
> > details like numa nodes, cores, threads and sockets.
> >
> > The new apic id decoding is mostly similar to current apic id decoding
> > except that it adds a new field node_id when numa configured. Removes all
> > the hardcoded values. Subsequent patches will use these functions to build
> > the topology.
> >
> > Following functions are added.
> > apicid_llc_width_epyc
> > apicid_llc_offset_epyc
> > apicid_pkg_offset_epyc
> > apicid_from_topo_ids_epyc
> > x86_topo_ids_from_idx_epyc
> > x86_topo_ids_from_apicid_epyc
> > x86_apicid_from_cpu_idx_epyc
> >
> > The topology details are available in Processor Programming Reference (PPR)
> > for AMD Family 17h Model 01h, Revision B1 Processors. The revision guides
> are
> > available from the bugzilla Link below.
> > Link:
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.
> kernel.org%2Fshow_bug.cgi%3Fid%3D206537&amp;data=02%7C01%7Cbabu.m
> oger%40amd.com%7C3487f40d37df4d59097d08d807190248%7C3dd8961fe488
> 4e608e11a82d994e183d%7C0%7C0%7C637267151289763739&amp;sdata=wE0
> ukXIVh0l5eNQWsv6VDE9UZEVJmisofaW192gcZAI%3D&amp;reserved=0
> >
> > Signed-off-by: Babu Moger <babu.moger@amd.com>
> > Acked-by: Igor Mammedov <imammedo@redhat.com>
> > Acked-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> [...]
> >  typedef struct X86CPUTopoIDs {
> >      unsigned pkg_id;
> > +    unsigned node_id;
> 
> You have added a new field here.
> 
> >      unsigned die_id;
> >      unsigned core_id;
> >      unsigned smt_id;
> [...]
> > +static inline apic_id_t
> > +x86_apicid_from_topo_ids_epyc(X86CPUTopoInfo *topo_info,
> > +                              const X86CPUTopoIDs *topo_ids)
> > +{
> > +    return (topo_ids->pkg_id  << apicid_pkg_offset_epyc(topo_info)) |
> > +           (topo_ids->node_id << apicid_node_offset_epyc(topo_info)) |
> 
> You are using the new field here.
> 
> > +           (topo_ids->die_id  << apicid_die_offset(topo_info)) |
> > +           (topo_ids->core_id << apicid_core_offset(topo_info)) |
> > +           topo_ids->smt_id;
> > +}
> 
> But you are not initializing node_id in one caller of apicid_from_topo_ids():
> 
> static void pc_cpu_pre_plug(HotplugHandler *hotplug_dev,
>                             DeviceState *dev, Error **errp)
> {
>     [...]
>     X86CPUTopoIDs topo_ids;
>     [...]
>     if (cpu->apic_id == UNASSIGNED_APIC_ID) {
>         [...]
>         topo_ids.pkg_id = cpu->socket_id;
>         topo_ids.die_id = cpu->die_id;
>         topo_ids.core_id = cpu->core_id;
>         topo_ids.smt_id = cpu->thread_id;
>         cpu->apic_id = x86ms->apicid_from_topo_ids(&topo_info, &topo_ids);
>     }
>     [...]
> }
> 
> Result: -device is broken when using -cpu EPYC:
> 
>   $ 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 patch should initialize the node_id. But I am not sure how to
reproduce the bug. Can you please send me the full command line to
reproduce the problem. Also test different options.

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 2128f3d6fe..047b4b9391 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1539,6 +1539,9 @@ static void pc_cpu_pre_plug(HotplugHandler *hotplug_dev,
     if (cpu->apic_id == UNASSIGNED_APIC_ID) {
         int max_socket = (ms->smp.max_cpus - 1) /
                                 smp_threads / smp_cores / x86ms->smp_dies;
+        unsigned nr_nodes = MAX(topo_info.nodes_per_pkg, 1);
+        unsigned cores_per_node = DIV_ROUND_UP((x86ms->smp_dies * smp_cores *
+                                                smp_threads), nr_nodes);

         /*
          * die-id was optional in QEMU 4.0 and older, so keep it optional
@@ -1585,6 +1588,7 @@ 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->core_id / cores_per_node) % nr_nodes;
         cpu->apic_id = x86ms->apicid_from_topo_ids(&topo_info, &topo_ids);
     }