Re: [PATCH v1 2/2] KVM: VMX: always require WB memory type for EPT

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Aug 10, 2017 at 04:42:02PM +0200, Paolo Bonzini wrote:
> On 10/08/2017 15:35, David Hildenbrand wrote:
> > We already always set that type but don't check if it is supported. Also
> > for nVMX, we only support WB for now. Let's just require it.
> > 
> > Signed-off-by: David Hildenbrand <david@redhat.com>
> 
> It may only happen on a broken nested hypervisor, so the patch is okay.

Is there one in the wild?
> 
> Paolo
> 
> > ---
> >  arch/x86/kvm/vmx.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > index f6638ed..023c6dc 100644
> > --- a/arch/x86/kvm/vmx.c
> > +++ b/arch/x86/kvm/vmx.c
> > @@ -1200,6 +1200,11 @@ static inline bool cpu_has_vmx_ept_4levels(void)
> >  	return vmx_capability.ept & VMX_EPT_PAGE_WALK_4_BIT;
> >  }
> >  
> > +static inline bool cpu_has_vmx_ept_mt_wb(void)
> > +{
> > +	return vmx_capability.ept & VMX_EPTP_WB_BIT;
> > +}
> > +
> >  static inline bool cpu_has_vmx_ept_ad_bits(void)
> >  {
> >  	return vmx_capability.ept & VMX_EPT_AD_BIT;
> > @@ -4302,7 +4307,6 @@ static u64 construct_eptp(struct kvm_vcpu *vcpu, unsigned long root_hpa)
> >  {
> >  	u64 eptp = VMX_EPTP_MT_WB | VMX_EPTP_PWL_4;
> >  
> > -	/* TODO write the value reading from MSR */
> >  	if (enable_ept_ad_bits &&
> >  	    (!is_guest_mode(vcpu) || nested_ept_ad_enabled(vcpu)))
> >  		eptp |= VMX_EPTP_AD_ENABLE_BIT;
> > @@ -6638,7 +6642,8 @@ static __init int hardware_setup(void)
> >  		init_vmcs_shadow_fields();
> >  
> >  	if (!cpu_has_vmx_ept() ||
> > -	    !cpu_has_vmx_ept_4levels()) {
> > +	    !cpu_has_vmx_ept_4levels() ||
> > +	    !cpu_has_vmx_ept_mt_wb()) {
> >  		enable_ept = 0;
> >  		enable_unrestricted_guest = 0;
> >  		enable_ept_ad_bits = 0;
> > 
>