Shouldn't there be an IBPB on *any* context switch away from a VCPU
thread, even if it is to a non-VCPU thread?
On Mon, Jan 8, 2018 at 10:08 AM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
> From: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
>
> Ensure an IBPB (Indirect branch prediction barrier) before every VCPU
> switch.
>
> Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> arch/x86/kvm/vmx.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index d00bcad7336e..bf127c570675 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2375,6 +2375,8 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> if (per_cpu(current_vmcs, cpu) != vmx->loaded_vmcs->vmcs) {
> per_cpu(current_vmcs, cpu) = vmx->loaded_vmcs->vmcs;
> vmcs_load(vmx->loaded_vmcs->vmcs);
> + if (have_spec_ctrl)
> + wrmsrl(MSR_IA32_PRED_CMD, FEATURE_SET_IBPB);
> }
>
> if (!already_loaded) {
> @@ -4029,6 +4031,13 @@ static void free_loaded_vmcs(struct loaded_vmcs *loaded_vmcs)
> free_vmcs(loaded_vmcs->vmcs);
> loaded_vmcs->vmcs = NULL;
> WARN_ON(loaded_vmcs->shadow_vmcs != NULL);
> +
> + /*
> + * The VMCS could be recycled, causing a false negative in
> + * vmx_vcpu_load; block speculative execution.
> + */
> + if (have_spec_ctrl)
> + wrmsrl(MSR_IA32_PRED_CMD, FEATURE_SET_IBPB);
> }
>
> static void vmx_nested_free_vmcs02(struct vcpu_vmx *vmx)
> --
> 1.8.3.1
>
>
