Xen PV guests in DomU have APIC disabled by design, which causes topology_apply_cmdline_limits_early() to limit the number of possible CPUs to 1, regardless of the configured number of vCPUs.
This is a regression introduced in version 6.9 in commit 7c0edad3643f ("x86/cpu/topology: Rework possible CPU management") which added an early check that limits CPUs if apic_is_disabled, without accounting for the fact that Xen PV guests always disable APIC even when SMP is supported.
This patch fixes the issue by skipping the apic_is_disabled check for Xen PV guests, allowing them to boot with the full set of configured vCPUs.
Fixes: 7c0edad3643f ("x86/cpu/topology: Rework possible CPU management") Cc: Thomas Gleixner tglx@linutronix.de Cc: x86@kernel.org Cc: xen-devel@lists.xenproject.org Cc: stable@vger.kernel.org # 6.9+ Signed-off-by: Petr Vaněk arkamar@atlas.cz --- arch/x86/kernel/cpu/topology.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c index 01456236a6dd..10aa7f471ec9 100644 --- a/arch/x86/kernel/cpu/topology.c +++ b/arch/x86/kernel/cpu/topology.c @@ -428,8 +428,13 @@ void __init topology_apply_cmdline_limits_early(void) { unsigned int possible = nr_cpu_ids;
- /* 'maxcpus=0' 'nosmp' 'nolapic' */ - if (!setup_max_cpus || apic_is_disabled) + /* 'maxcpus=0' 'nosmp' 'nolapic' + * + * The apic_is_disabled check is ignored for Xen PV domains because Xen + * disables ACPI in unprivileged PV DomU guests, which would otherwise limit + * CPUs to 1, even if multiple vCPUs were configured. + */ + if (!setup_max_cpus || (!xen_pv_domain() && apic_is_disabled)) possible = 1;
/* 'possible_cpus=N' */