[PATCH 1/2] x86/cpu hotplug: make apicid <--> cpuid mapping persistent

[Gu Zheng]

Previously, we build the apicid <--> cpuid mapping when the cpu is present, but
the relationship will be changed if the cpu/node hotplug happenned, because we
always choose the first free cpuid for the hot added cpu (whether it is new-add
or re-add), so this the cpuid <--> node mapping changed if node hot plug
occurred, and it causes the wq sub-system allocation failture:
  ==
     SLUB: Unable to allocate memory on node 2 (gfp=0x80d0)
      cache: kmalloc-192, object size: 192, buffer size: 192, default
order:
    1, min order: 0
      node 0: slabs: 6172, objs: 259224, free: 245741
      node 1: slabs: 3261, objs: 136962, free: 127656
  ==
So here we build the persistent [lapic id] <--> cpuid mapping when the cpu first
present, and never change it.

Suggested-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Signed-off-by: Gu Zheng <guz.fnst@xxxxxxxxxxxxxx>
---
 arch/x86/kernel/apic/apic.c |   31 ++++++++++++++++++++++++++++++-
 1 files changed, 30 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index ad3639a..d539ebc 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -2038,6 +2038,30 @@ void disconnect_bsp_APIC(int virt_wire_setup)
 	apic_write(APIC_LVT1, value);
 }
 
+/*
+ * Logic cpu number(cpuid) to local APIC id persistent mappings.
+ * Do not clear the mapping even if cpu hot removed.
+ * */
+static int apicid_to_x86_cpu[MAX_LOCAL_APIC] = {
+	[0 ... MAX_LOCAL_APIC - 1] = -1,
+};
+
+/*
+ * Internal cpu id bits, set the bit once cpu present, and never clear it.
+ * */
+static cpumask_t cpuid_mask = CPU_MASK_NONE;
+
+static int get_cpuid(int apicid)
+{
+	int cpuid;
+
+	cpuid = apicid_to_x86_cpu[apicid];
+	if (cpuid == -1)
+		cpuid = cpumask_next_zero(-1, &cpuid_mask);
+
+	return cpuid;
+}
+
 int generic_processor_info(int apicid, int version)
 {
 	int cpu, max = nr_cpu_ids;
@@ -2115,7 +2139,10 @@ int generic_processor_info(int apicid, int version)
 		 */
 		cpu = 0;
 	} else
-		cpu = cpumask_next_zero(-1, cpu_present_mask);
+		cpu = get_cpuid(apicid);
+
+	/* Store the mapping */
+	apicid_to_x86_cpu[apicid] = cpu;
 
 	/*
 	 * Validate version
@@ -2144,6 +2171,8 @@ int generic_processor_info(int apicid, int version)
 	early_per_cpu(x86_cpu_to_logical_apicid, cpu) =
 		apic->x86_32_early_logical_apicid(cpu);
 #endif
+	/* Mark this cpu id as uesed (already mapping a local apic id) */
+	cpumask_set_cpu(cpu, &cpuid_mask);
 	set_cpu_possible(cpu, true);
 	set_cpu_present(cpu, true);
 
-- 
1.7.7

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