Xen domU instances do not boot on x86 with ACPI enabled, so the entire ACPI subsystem is ultimately disabled. This causes acpi_mps_check() to trigger a warning that the ACPI MPS table is not present, which then disables APIC support on domU, breaking the CPU topology detection for all vCPUs other than the boot vCPU.

Fixes: 7c0edad3643f ("x86/cpu/topology: Rework possible CPU management") Signed-off-by: Ariadne Conill ariadne@ariadne.space Cc: x86@kernel.org Cc: Thomas Gleixner tglx@linutronix.de Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org --- arch/x86/kernel/cpu/topology.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c index 621a151ccf7d..38fa5ed816d6 100644 --- a/arch/x86/kernel/cpu/topology.c +++ b/arch/x86/kernel/cpu/topology.c @@ -429,7 +429,7 @@ void __init topology_apply_cmdline_limits_early(void) unsigned int possible = nr_cpu_ids;

/* 'maxcpus=0' 'nosmp' 'nolapic' 'disableapic' 'noapic' */ - if (!setup_max_cpus || ioapic_is_disabled || apic_is_disabled) + if (!setup_max_cpus || ioapic_is_disabled || (apic_is_disabled && !xen_pv_domain())) possible = 1;

/* 'possible_cpus=N' */