Re: [PATCH 8/9] KVM/VMX: Allow direct access to MSR_IA32_SPEC_CTRL

On Tue, Feb 6, 2018 at 9:29 AM, David Woodhouse dwmw@amazon.co.uk wrote:

@@ -8828,6 +8890,15 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)

    vmx_arm_hv_timer(vcpu);

•   /*
  

•    * If this vCPU has touched SPEC_CTRL, restore the guest's value if
  

•    * it's non-zero. Since vmentry is serialising on affected CPUs, there
  

•    * is no need to worry about the conditional branch over the wrmsr
  

•    * being speculatively taken.
  

•    */
  

•   if (vmx->spec_ctrl)
  

•           wrmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl);
  

Shouldn't this be wrmsrl_safe? Userspace can make an ioctl to set vmx->spec_ctrl to non-zero even if the MSR is not supported on the host.