> -----Original Message-----
> From: Eduardo Habkost <ehabk...@redhat.com>
> Sent: Wednesday, June 3, 2020 10:46 AM
> To: Moger, Babu <babu.mo...@amd.com>
> Cc: marcel.apfelb...@gmail.com; pbonz...@redhat.com; r...@twiddle.net;
> m...@redhat.com; imamm...@redhat.com; qemu-devel@nongnu.org
> Subject: Re: [PATCH v7 07/13] hw/386: Add EPYC mode topology decoding
> functions
>
> On Wed, Jun 03, 2020 at 10:38:46AM -0500, Babu Moger wrote:
> >
> >
> > On 6/3/20 10:31 AM, Eduardo Habkost wrote:
> > > On Wed, Jun 03, 2020 at 10:22:10AM -0500, Babu Moger wrote:
> > >>
> > >>
> > >>> -----Original Message-----
> > >>> From: Eduardo Habkost <ehabk...@redhat.com>
> > >>> Sent: Tuesday, June 2, 2020 6:01 PM
> > >>> To: Moger, Babu <babu.mo...@amd.com>
> > >>> Cc: marcel.apfelb...@gmail.com; pbonz...@redhat.com;
> r...@twiddle.net;
> > >>> m...@redhat.com; imamm...@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 <ehabk...@redhat.com>
> > >>>>> Sent: Tuesday, June 2, 2020 12:19 PM
> > >>>>> To: Moger, Babu <babu.mo...@amd.com>
> > >>>>> Cc: marcel.apfelb...@gmail.com; pbonz...@redhat.com;
> r...@twiddle.net;
> > >>>>> m...@redhat.com; imamm...@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&data=02%7C01%7Cbabu.m
> > >>>>>
> > >>>
> oger%40amd.com%7C3487f40d37df4d59097d08d807190248%7C3dd8961fe488
> > >>>>>
> > >>>
> 4e608e11a82d994e183d%7C0%7C0%7C637267151289763739&sdata=wE0
> > >>>>> ukXIVh0l5eNQWsv6VDE9UZEVJmisofaW192gcZAI%3D&reserved=0
> > >>>>>>
> > >>>>>> Signed-off-by: Babu Moger <babu.mo...@amd.com>
> > >>>>>> Acked-by: Igor Mammedov <imamm...@redhat.com>
> > >>>>>> Acked-by: Michael S. Tsirkin <m...@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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.qem
> u.org%2Fgit%2Fqemu.git&data=02%7C01%7Cbabu.moger%40amd.com%7
> C4b409b77ff2c4c4ed90608d807d53570%7C3dd8961fe4884e608e11a82d994e1
> 83d%7C0%7C0%7C637267959601716206&sdata=ih6bo9Wp0RbJgRpryzSa2
> D0v6kr3Zfww%2B1uB%2FNyngk8%3D&reserved=0 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.
> >
> > [2]
> >
> > >>
> > >>>
> > >>>
> > >>>>
> > >>>> 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.
> > >
> > > I assumed core_id identified the core inside a die, and the range
> > > would be [0, cores_per_die). This seems to be what
> > > apicid_from_topo_ids_epyc() expects.
> > >
> > > We need clearer documentation on the semantics of each *_id
> > > field, to avoid confusion.
> >
> > Ok. Sure. I will add that. Can you please clarify on how to repro the
> > issue. Marked the question at [2].
>
> As it is usage of uninitialized memory, behavior is undefined and
> not guaranteed to crash. My QEMU binary was built with
> --enable-debug, maybe it makes it easier to reproduce.
This patch works fine. Tested few combination. Will send the formal
version if patch looks good.
diff --git a/include/hw/i386/topology.h b/include/hw/i386/topology.h
index 07239f95f4..cb28f0a57c 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);
+}
/*
* Make APIC ID for the CPU based on Pkg_ID, Core_ID, SMT_ID
*
@@ -149,8 +160,11 @@ static inline apic_id_t
x86_apicid_from_topo_ids_epyc(X86CPUTopoInfo *topo_info,
const X86CPUTopoIDs *topo_ids)
{
+ /* node_id can be uninitialized. Initialize here */
+ unsigned node_id = x86_node_id_for_epyc(topo_info, topo_ids);
+
return (topo_ids->pkg_id << apicid_pkg_offset_epyc(topo_info)) |
- (topo_ids->node_id << apicid_node_offset_epyc(topo_info)) |
+ (node_id << apicid_node_offset_epyc(topo_info)) |
(topo_ids->die_id << apicid_die_offset(topo_info)) |
(topo_ids->core_id << apicid_core_offset(topo_info)) |
topo_ids->smt_id;
