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Date: Wed, 10 Apr 2024 13:33:17 -0000
From: "tip-bot2 for Thomas Gleixner" <tip-bot2@linutronix.de>
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Subject: [tip: x86/alternatives] x86/topology: Don't update cpu_possible_map
 in topo_set_cpuids()
Cc: Jonathan Cameron <Jonathan.Cameron@Huawei.com>,
 Thomas Gleixner <tglx@linutronix.de>, x86@kernel.org,
 linux-kernel@vger.kernel.org
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The following commit has been merged into the x86/alternatives branch of tip:

Commit-ID:     675ae1aac0572595999e6f78a16e51351291f7aa
Gitweb:        https://git.kernel.org/tip/675ae1aac0572595999e6f78a16e51351291f7aa
Author:        Thomas Gleixner <tglx@linutronix.de>
AuthorDate:    Mon, 08 Apr 2024 15:22:01 +02:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Wed, 10 Apr 2024 15:24:27 +02:00

x86/topology: Don't update cpu_possible_map in topo_set_cpuids()

topo_set_cpuids() updates cpu_present_map and cpu_possible map. It is
invoked during enumeration and "physical hotplug" operations. In the
latter case this results in a kernel crash because cpu_possible_map is
marked read only after init completes.

There is no reason to update cpu_possible_map in that function. During
enumeration cpu_possible_map is not relevant and gets fully initialized
after enumeration completed. On "physical hotplug" the bit is already set
because the kernel allows only CPUs to be plugged which have been
enumerated and associated to a CPU number during early boot.

Remove the bogus update of cpu_possible_map.

Fixes: 0e53e7b656cf ("x86/cpu/topology: Sanitize the APIC admission logic")
Reported-by: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/87ttkc6kwx.ffs@tglx

---
 arch/x86/kernel/cpu/topology.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c
index aaca8d2..d17c9b7 100644
--- a/arch/x86/kernel/cpu/topology.c
+++ b/arch/x86/kernel/cpu/topology.c
@@ -123,7 +123,6 @@ static void topo_set_cpuids(unsigned int cpu, u32 apic_id, u32 acpi_id)
 	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);
 	set_cpu_present(cpu, true);
 }
 
@@ -210,7 +209,11 @@ static __init void topo_register_apic(u32 apic_id, u32 acpi_id, bool present)
 		topo_info.nr_disabled_cpus++;
 	}
 
-	/* Register present and possible CPUs in the domain maps */
+	/*
+	 * Register present and possible CPUs in the domain
+	 * maps. cpu_possible_map will be updated in
+	 * topology_init_possible_cpus() after enumeration is done.
+	 */
 	for (dom = TOPO_SMT_DOMAIN; dom < TOPO_MAX_DOMAIN; dom++)
 		set_bit(topo_apicid(apic_id, dom), apic_maps[dom].map);
 }