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Re: [PATCH v2 3/3] hw/386: Fix uninitialized memory with -device and CPU
From: |
Igor Mammedov |
Subject: |
Re: [PATCH v2 3/3] hw/386: Fix uninitialized memory with -device and CPU hotplug |
Date: |
Mon, 27 Jul 2020 18:36:12 +0200 |
On Wed, 01 Jul 2020 12:31:15 -0500
Babu Moger <babu.moger@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.GG577771@habkost.net/
>
> Fix the problem by initializing the node_id from the device being added.
>
> Fixes:
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=1828750
>
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> ---
> hw/i386/pc.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index e613b2299f..aa9fb48834 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -1553,6 +1553,15 @@ static void pc_cpu_pre_plug(HotplugHandler
> *hotplug_dev,
> cpu->die_id = 0;
> }
>
so this is from
'if (cpu->apic_id == UNASSIGNED_APIC_ID) {'
branch, meaning cpu comes from -device/device_add
> + /*
> + * If node_id is not set, initialize it to zero for now. If the user
> + * does not pass the correct node in case of numa configuration, it
> + * will be rejected eventually.
> + */
> + if (cpu->node_id < 0) {
which means that user hasn't provided 'node-id',
in which case we should error out asking for specifying NUMA node-id along with
other options
(1)
However that's not enough since by contract query-hotpluggbale-cpus shall
provide all attributes
necessary to hotplug CPU, which makes node-id is not an optional in case of
EPYC cpu.
So we need to initialize ms->possible_cpus->cpus[i].props.[has_]node_id by the
time
we start creating CPUs.
here are 2 variants:
(2)
* single node:
nodes_per_pkg 1 and ms->smp.sockets == 1
since it's the only node and mapping of RAM/CPU is unambigiuos,
we can deal with it by moving auto_enable_numa into MachineState
and enabling it in case EPYC CPU is used
* multiple nodes:
- ms->smp.sockets > 1
- nodes_per_pkg > 1
we can't make up NUMA nodes automatically, and have to ask user to use
-numa options
to provide nodes along with CPU/RAM mapping. So in case NUMA wasn't
configured
explicitly, we can only error out. (that also applies to CPU created
implicitly by board '-smp X')
(3) Once user supplied mapping we need to checks that it matches EPYC topology,
(4) As for CPUID, current code in CPUID_Fn8000001E_ECX
if (nodes <= 4) { /* here nodes is nodes_per_pkg */
/ goes by stricly spec /
*ecx = ((nodes - 1) << 8) | (topo_ids.pkg_id << 2) | topo_ids.node_id;
/* makes up system wide NUMA node IDs which happen to match system wide
NUMA node IDs created by -numa, when -smp + -numa produces
nodes_per_pkg is in that range,
basically user has no idea when this happens
*/
} else {
/* makeup new algorithm system wide NUMA node IDs generation for out
of spec behaviour */
}
problem with both branches is that might lead to inconsistentcy between
system wide
NUMA node id in CPUID_Fn8000001E_ECX and the one configured with -numa
which goes to
SRAT ACPI table and should go to CPU::node-id property.
Considering that out of spec behaviour is allowed we probably schould
replace both branches
with
*ecx = ((nodes - 1) << 8) | cpu->node_id;
which ensures consistency of system wide NUMA node ids and add checks for
max nodes/max node id.
checks could be done early in cpu's realize() function.
> + cpu->node_id = 0;
> + }
> if (cpu->socket_id < 0) {
> error_setg(errp, "CPU socket-id is not set");
> return;
> @@ -1587,6 +1596,7 @@ static void pc_cpu_pre_plug(HotplugHandler *hotplug_dev,
> }
>
> topo_ids.pkg_id = cpu->socket_id;
> + topo_ids.node_id = cpu->node_id;
> topo_ids.die_id = cpu->die_id;
> topo_ids.core_id = cpu->core_id;
> topo_ids.smt_id = cpu->thread_id;
>
[PATCH v2 2/3] hw/i386: Build apic_id from CpuInstanceProperties, Babu Moger, 2020/07/01
[PATCH v2 3/3] hw/386: Fix uninitialized memory with -device and CPU hotplug, Babu Moger, 2020/07/01
- Re: [PATCH v2 3/3] hw/386: Fix uninitialized memory with -device and CPU hotplug,
Igor Mammedov <=