linux-kernel - [PATCH 1/2] x86/cpu/topology: don't write to immutable cpu_present

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Date: Sun,  7 Apr 2024 18:26:43 +0300
From: Alexey Dobriyan <adobriyan@...il.com>
To: tglx@...utronix.de
Cc: adobriyan@...il.com,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	x86@...nel.org,
	hpa@...or.com,
	linux-kernel@...r.kernel.org,
	peterz@...radead.org,
	Jonathan.Cameron@...wei.com,
	linuxarm@...wei.com,
	linux@...ck-us.net,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: [PATCH 1/2] x86/cpu/topology: don't write to immutable cpu_present_mask

Workaround the following oops:

	topology_hotplug_apic
	topo_set_cpuids
		set_cpu_possible(cpu, true);
		// write to __ro_after_init section after init

adobriyan: I'm not sure what's going on, can it set unset bit here?
If not, then why does it repeat the job and set already set bits.

Anyhow, let's not oops peoples' machines for now.

Reported-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Suggested-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---
 arch/x86/kernel/cpu/topology.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c
index aaca8d235dc2..42f4a17f8019 100644
--- a/arch/x86/kernel/cpu/topology.c
+++ b/arch/x86/kernel/cpu/topology.c
@@ -117,13 +117,18 @@ static __init int topo_get_cpunr(u32 apic_id)
 	return topo_info.nr_assigned_cpus++;
 }
 
-static void topo_set_cpuids(unsigned int cpu, u32 apic_id, u32 acpi_id)
+static void topo_set_cpuids(unsigned int cpu, u32 apic_id, u32 acpi_id, bool from_init)
 {
 #if defined(CONFIG_SMP) || defined(CONFIG_X86_64)
 	early_per_cpu(x86_cpu_to_apicid, cpu) = apic_id;
 	early_per_cpu(x86_cpu_to_acpiid, cpu) = acpi_id;
 #endif
-	set_cpu_possible(cpu, true);
+	if (from_init) {
+		set_cpu_possible(cpu, true);
+	} else {
+		/* cpu_possible_mask is supposed to be fixed by now. */
+		WARN_ON(!cpumask_test_cpu(cpu, cpu_possible_mask));
+	}
 	set_cpu_present(cpu, true);
 }
 
@@ -191,7 +196,7 @@ static __init void topo_register_apic(u32 apic_id, u32 acpi_id, bool present)
 			cpu = topo_get_cpunr(apic_id);
 
 		cpuid_to_apicid[cpu] = apic_id;
-		topo_set_cpuids(cpu, apic_id, acpi_id);
+		topo_set_cpuids(cpu, apic_id, acpi_id, true);
 	} else {
 		u32 pkgid = topo_apicid(apic_id, TOPO_PKG_DOMAIN);
 
@@ -343,7 +348,7 @@ int topology_hotplug_apic(u32 apic_id, u32 acpi_id)
 		return -ENOSPC;
 
 	set_bit(apic_id, phys_cpu_present_map);
-	topo_set_cpuids(cpu, apic_id, acpi_id);
+	topo_set_cpuids(cpu, apic_id, acpi_id, false);
 	cpu_mark_primary_thread(cpu, apic_id);
 	return cpu;
 }
-- 
2.43.2