Re: [PATCH 4/7] kvm: vmx: Set IBPB when running a different VCPU

[Liran Alon]

On 08/01/18 20:08, Paolo Bonzini 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)

Reviewed-by: Liran Alon <liran.alon@xxxxxxxxxx>