4.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Zhang Rui <rui.zhang@xxxxxxxxx>
[ Upstream commit edc0a2b5957652f4685ef3516f519f84807087db ]
Traditionally, all CPUs in a system have identical numbers of SMT
siblings. That changes with hybrid processors where some logical CPUs
have a sibling and others have none.
Today, the CPU boot code sets the global variable smp_num_siblings when
every CPU thread is brought up. The last thread to boot will overwrite
it with the number of siblings of *that* thread. That last thread to
boot will "win". If the thread is a Pcore, smp_num_siblings == 2. If it
is an Ecore, smp_num_siblings == 1.
smp_num_siblings describes if the *system* supports SMT. It should
specify the maximum number of SMT threads among all cores.
Ensure that smp_num_siblings represents the system-wide maximum number
of siblings by always increasing its value. Never allow it to decrease.
On MeteorLake-P platform, this fixes a problem that the Ecore CPUs are
not updated in any cpu sibling map because the system is treated as an
UP system when probing Ecore CPUs.
Below shows part of the CPU topology information before and after the
fix, for both Pcore and Ecore CPU (cpu0 is Pcore, cpu 12 is Ecore).
...
-/sys/devices/system/cpu/cpu0/topology/package_cpus:000fff
-/sys/devices/system/cpu/cpu0/topology/package_cpus_list:0-11
+/sys/devices/system/cpu/cpu0/topology/package_cpus:3fffff
+/sys/devices/system/cpu/cpu0/topology/package_cpus_list:0-21
...
-/sys/devices/system/cpu/cpu12/topology/package_cpus:001000
-/sys/devices/system/cpu/cpu12/topology/package_cpus_list:12
+/sys/devices/system/cpu/cpu12/topology/package_cpus:3fffff
+/sys/devices/system/cpu/cpu12/topology/package_cpus_list:0-21
Notice that the "before" 'package_cpus_list' has only one CPU. This
means that userspace tools like lscpu will see a little laptop like
an 11-socket system:
-Core(s) per socket: 1
-Socket(s): 11
+Core(s) per socket: 16
+Socket(s): 1
This is also expected to make the scheduler do rather wonky things
too.
[ dhansen: remove CPUID detail from changelog, add end user effects ]
CC: stable@xxxxxxxxxx
Fixes: bbb65d2d365e ("x86: use cpuid vector 0xb when available for detecting cpu topology")
Fixes: 95f3d39ccf7a ("x86/cpu/topology: Provide detect_extended_topology_early()")
Suggested-by: Len Brown <len.brown@xxxxxxxxx>
Signed-off-by: Zhang Rui <rui.zhang@xxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/all/20230323015640.27906-1-rui.zhang%40intel.com
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
arch/x86/kernel/cpu/topology.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c
index 71ca064e37948..31fe56a90cbf8 100644
--- a/arch/x86/kernel/cpu/topology.c
+++ b/arch/x86/kernel/cpu/topology.c
@@ -44,7 +44,7 @@ int detect_extended_topology_early(struct cpuinfo_x86 *c)
* initial apic id, which also represents 32-bit extended x2apic id.
*/
c->initial_apicid = edx;
- smp_num_siblings = LEVEL_MAX_SIBLINGS(ebx);
+ smp_num_siblings = max_t(int, smp_num_siblings, LEVEL_MAX_SIBLINGS(ebx));
#endif
return 0;
}
@@ -68,7 +68,8 @@ int detect_extended_topology(struct cpuinfo_x86 *c)
* Populate HT related information from sub-leaf level 0.
*/
cpuid_count(0xb, SMT_LEVEL, &eax, &ebx, &ecx, &edx);
- core_level_siblings = smp_num_siblings = LEVEL_MAX_SIBLINGS(ebx);
+ core_level_siblings = LEVEL_MAX_SIBLINGS(ebx);
+ smp_num_siblings = max_t(int, smp_num_siblings, LEVEL_MAX_SIBLINGS(ebx));
core_plus_mask_width = ht_mask_width = BITS_SHIFT_NEXT_LEVEL(eax);
sub_index = 1;
--
2.40.1
