th "Enabled=0" it is expected that the OS will completely ignore these entries. However, QEMU will do the same (include entries with "Enabled=0") for the purpose of allowing CPU hotplug within the guest. Comment from QEMU function pc_madt_cpu_entry(): /* ACPI spec says that LAPIC entry for non present * CPU may be omitted from MADT or it must be marked * as disabled. However omitting non present CPU from * MADT breaks hotplug on linux. So possible CPUs * should be put in MADT but kept disabled. */ Recent Linux topology changes broke the QEMU use case. A following fix for the QEMU use case broke bare metal topology enumeration. Rework the Linux MADT LAPIC flags check to allow the QEMU use case only for guests and to maintain the ACPI spec behavior for bare metal. Remove an unnecessary check added to fix a bare metal case introduced by the QEMU "fix". [ bp: Change logic as Michal suggested. ] [ mingo: Removed misapplied -stable tag. ] Fixes: fed8d8773b8e ("x86/acpi/boot: Correct acpi_is_processor_usable() check") Fixes: f0551af02130 ("x86/topology: Ignore non-present APIC IDs in a present package") Closes: https://lore.kernel.org/r/20251024204658.3da9bf3f.michal.pecio@gmail.com Reported-by: Michal Pecio Signed-off-by: Yazen Ghannam Signed-off-by: Borislav Petkov (AMD) Signed-off-by: Ingo Molnar Tested-by: Michal Pecio Tested-by: Ricardo Neri Link: https://lore.kernel.org/20251111145357.4031846-1-yazen.ghannam@amd.com Cc: stable@vger.kernel.org Signed-off-by: Sasha Levin --- arch/x86/kernel/acpi/boot.c | 12 ++++++++---- arch/x86/kernel/cpu/topology.c | 15 --------------- 2 files changed, 8 insertions(+), 19 deletions(-) diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c index 9fa321a95eb33..d6138b2b633a3 100644 --- a/arch/x86/kernel/acpi/boot.c +++ b/arch/x86/kernel/acpi/boot.c @@ -35,6 +35,7 @@ #include #include #include +#include #include "sleep.h" /* To include x86_acpi_suspend_lowlevel */ static int __initdata acpi_force = 0; @@ -164,11 +165,14 @@ static bool __init acpi_is_processor_usable(u32 lapic_flags) if (lapic_flags & ACPI_MADT_ENABLED) return true; - if (!acpi_support_online_capable || - (lapic_flags & ACPI_MADT_ONLINE_CAPABLE)) - return true; + if (acpi_support_online_capable) + return lapic_flags & ACPI_MADT_ONLINE_CAPABLE; - return false; + /* + * QEMU expects legacy "Enabled=0" LAPIC entries to be counted as usable + * in order to support CPU hotplug in guests. + */ + return !hypervisor_is_type(X86_HYPER_NATIVE); } static int __init diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c index f55ea3cdbf88e..23190a786d310 100644 --- a/arch/x86/kernel/cpu/topology.c +++ b/arch/x86/kernel/cpu/topology.c @@ -27,7 +27,6 @@ #include #include -#include #include #include #include @@ -236,20 +235,6 @@ static __init void topo_register_apic(u32 apic_id, u32 acpi_id, bool present) cpuid_to_apicid[cpu] = apic_id; topo_set_cpuids(cpu, apic_id, acpi_id); } else { - u32 pkgid = topo_apicid(apic_id, TOPO_PKG_DOMAIN); - - /* - * Check for present APICs in the same package when running - * on bare metal. Allow the bogosity in a guest. - */ - if (hypervisor_is_type(X86_HYPER_NATIVE) && - topo_unit_count(pkgid, TOPO_PKG_DOMAIN, phys_cpu_present_map)) { - pr_info_once("Ignoring hot-pluggable APIC ID %x in present package.\n", - apic_id); - topo_info.nr_rejected_cpus++; - return; - } - topo_info.nr_disabled_cpus++; } -- 2.51.0[PATCH 6.19 504/844] x86/acpi/boot: Correct acpi_is_processor_usable() check againSasha Levin undefinedlinux-kernel@vger.kernel.org, stable@vger.kernel.org undefined undefined undefined undefined undefined undefined undefined