From: Li RongQing <lirongqing@xxxxxxxxx> commit c15e0ae42c8e5a61e9aca8aac920517cf7b3e94e upstream. If apic_id is less than min, and (max - apic_id) is greater than KVM_IPI_CLUSTER_SIZE, then the third check condition is satisfied but the new apic_id does not fit the bitmask. In this case __send_ipi_mask should send the IPI. This is mostly theoretical, but it can happen if the apic_ids on three iterations of the loop are for example 1, KVM_IPI_CLUSTER_SIZE, 0. Fixes: aaffcfd1e82 ("KVM: X86: Implement PV IPIs in linux guest") Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx> Message-Id: <1646814944-51801-1-git-send-email-lirongqing@xxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/kernel/kvm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -517,7 +517,7 @@ static void __send_ipi_mask(const struct } else if (apic_id < min && max - apic_id < KVM_IPI_CLUSTER_SIZE) { ipi_bitmap <<= min - apic_id; min = apic_id; - } else if (apic_id < min + KVM_IPI_CLUSTER_SIZE) { + } else if (apic_id > min && apic_id < min + KVM_IPI_CLUSTER_SIZE) { max = apic_id < max ? max : apic_id; } else { ret = kvm_hypercall4(KVM_HC_SEND_IPI, (unsigned long)ipi_bitmap,