When CONFIG_SMP is disabled, build failed like this: arch/x86/kernel/kvm.c: In function ‘kvm_alloc_cpumask’: arch/x86/kernel/kvm.c:823:35: error: ‘kvm_send_ipi_mask_allbutself’ undeclared (first use in this function); did you mean ‘apic_send_IPI_allbutself’? apic->send_IPI_mask_allbutself = kvm_send_ipi_mask_allbutself; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ apic_send_IPI_allbutself arch/x86/kernel/kvm.c:823:35: note: each undeclared identifier is reported only once for each function it appears in It is because the declaration of kvm_send_ipi_mask_allbutself() is guarded by CONFIG_SMP. kvm_send_ipi_mask_allbutself() do not need do anything at this time. Signed-off-by: Wang ShaoBo <bobo.shaobowang@xxxxxxxxxx> --- arch/x86/kernel/kvm.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index a44398d2bc44..47d65864e29c 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -611,6 +611,13 @@ static int kvm_cpu_down_prepare(unsigned int cpu) local_irq_enable(); return 0; } + +#else /* !CONFIG_SMP */ + +static void kvm_send_ipi_mask_allbutself(const struct cpumask *mask, int vector) +{ +} + #endif static void kvm_flush_tlb_others(const struct cpumask *cpumask, -- 2.25.1