On Fri, Sep 03, 2021, Vitaly Kuznetsov wrote: > Jiang Jiasheng <jiasheng@xxxxxxxxxxx> writes: > > > The kvm_get_vcpu() will call for the array_index_nospec() > > with the value of atomic_read(&(v->kvm)->online_vcpus) as size, > > and the value of constant '0' as index. > > If the size is also '0', it will be unreasonabe > > that the index is no less than the size. > > > > Can this really happen? > > 'online_vcpus' is never decreased, it is increased with every > kvm_vm_ioctl_create_vcpu() call when a new vCPU is created and is set to > 0 when all vCPUs are destroyed (kvm_free_vcpus()). > > kvm_guest_time_update() takes a vcpu as a parameter, this means that at > least 1 vCPU is currently present so 'online_vcpus' just can't be zero. Agreed, but doing kvm_get_vcpu() is ugly and overkill. diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 86539c1686fa..cc1cb9a401cd 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2969,7 +2969,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) offsetof(struct compat_vcpu_info, time)); if (vcpu->xen.vcpu_time_info_set) kvm_setup_pvclock_page(v, &vcpu->xen.vcpu_time_info_cache, 0); - if (v == kvm_get_vcpu(v->kvm, 0)) + if (!kvm_vcpu_get_idx(v)) kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock); return 0; }