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 6:01 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
> 
> On Tue, Jun 02, 2020 at 04:59:19PM -0500, Babu Moger wrote:
> >
> >
> > > -----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
> 
> [1]
> 
> > >   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.
> 
> The full command line is above[1].

I just picked up the latest tree from
git clone https://git.qemu.org/git/qemu.git qemu
Not seeing the problem.

./x86_64-softmmu/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
VNC server running on ::1:5900

It appears to run ok.

> 
> 
> >
> > 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;
> 
> So, here's the input you are using to calculate topo_ids.node_id:
> 
> > +        unsigned nr_nodes = MAX(topo_info.nodes_per_pkg, 1);
> 
> When is topo_info.nodes_per_pkg allowed to be 0?

It will be zero if numa is not configured. Node_id will be zero for all
the cores.

> 
> > +        unsigned cores_per_node = DIV_ROUND_UP((x86ms->smp_dies *
> smp_cores *
> > +                                                smp_threads), nr_nodes);
> 
> x86ms->smp_dies should be available at topo_info.dies_per_pkg,
> smp_cores should available at topo_info.cores_per_die,
> smp_threads should be available at topo_info.threads_per_core,
> nr_nodes should be available at topo_info.nodes_per_pkg.
> 
> >
> >          /*
> >           * 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;
> 
> apicid_from_topo_ids() have access to topo_info and topo_ids, If
> all the information you need to calculate node_id is already
> available inside topo_info + topo_ids, we could be calculating it
> inside apicid_from_topo_ids().  Why don't we do it?
> 
> Also, is topo_ids.core_id really allowed to be larger than
> cores_per_node when calling apicid_from_topo_ids()?

Yes. It is. If we have two numa nodes and 8 cores. Then cores_per_node is
4. Nr_nodes =2. Yes. Core_id can be larger than cores_per_node.

> 
> >          cpu->apic_id = x86ms->apicid_from_topo_ids(&topo_info, &topo_ids);
> >      }
> >
> 
> --
> Eduardo