linux-kernel - Re: [PATCH] KVM: nVMX: Add CET entry/exit load bits to evmcs unsupported list

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Date:   Thu, 4 Mar 2021 14:10:55 +0800
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Yang Weijiang <weijiang.yang@...el.com>, pbonzini@...hat.com,
        seanjc@...gle.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: nVMX: Add CET entry/exit load bits to evmcs
 unsupported list

On Wed, Mar 03, 2021 at 10:36:40AM +0100, Vitaly Kuznetsov wrote:
> Yang Weijiang <weijiang.yang@...el.com> writes:
> 
> > CET in nested guest over Hyper-V is not supported for now. Relevant
> > enabling patches will be posted as a separate patch series.
> >
> > Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
> > Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> > ---
> >  arch/x86/kvm/vmx/evmcs.h | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kvm/vmx/evmcs.h b/arch/x86/kvm/vmx/evmcs.h
> > index bd41d9462355..25588694eb04 100644
> > --- a/arch/x86/kvm/vmx/evmcs.h
> > +++ b/arch/x86/kvm/vmx/evmcs.h
> > @@ -59,8 +59,10 @@ DECLARE_STATIC_KEY_FALSE(enable_evmcs);
> >  	 SECONDARY_EXEC_SHADOW_VMCS |					\
> >  	 SECONDARY_EXEC_TSC_SCALING |					\
> >  	 SECONDARY_EXEC_PAUSE_LOOP_EXITING)
> > -#define EVMCS1_UNSUPPORTED_VMEXIT_CTRL (VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL)
> > -#define EVMCS1_UNSUPPORTED_VMENTRY_CTRL (VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL)
> > +#define EVMCS1_UNSUPPORTED_VMEXIT_CTRL (VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL | \
> > +					VM_EXIT_LOAD_CET_STATE)
> > +#define EVMCS1_UNSUPPORTED_VMENTRY_CTRL (VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL | \
> > +					 VM_ENTRY_LOAD_CET_STATE)
> >  #define EVMCS1_UNSUPPORTED_VMFUNC (VMX_VMFUNC_EPTP_SWITCHING)
> >  
> >  #if IS_ENABLED(CONFIG_HYPERV)
> 
> This should be enough when we run KVM on Hyper-V using eVMCS, however,
> it may not suffice when we run Hyper-V on KVM using eVMCS: there's still
> no corresponding eVMCS fields so CET can't be used. In case Hyper-V is
> smart enough it won't use the feature, however, it was proven to be 'not
> very smart' in the past, see nested_evmcs_filter_control_msr(). I'm
> wondering if we should also do
> 
> diff --git a/arch/x86/kvm/vmx/evmcs.c b/arch/x86/kvm/vmx/evmcs.c
> index 41f24661af04..9f81db51fd8b 100644
> --- a/arch/x86/kvm/vmx/evmcs.c
> +++ b/arch/x86/kvm/vmx/evmcs.c
> @@ -351,11 +351,11 @@ void nested_evmcs_filter_control_msr(u32 msr_index, u64 *pdata)
>         switch (msr_index) {
>         case MSR_IA32_VMX_EXIT_CTLS:
>         case MSR_IA32_VMX_TRUE_EXIT_CTLS:
> -               ctl_high &= ~VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL;
> +               ctl_high &= ~EVMCS1_UNSUPPORTED_VMEXIT_CTRL;
>                 break;
>         case MSR_IA32_VMX_ENTRY_CTLS:
>         case MSR_IA32_VMX_TRUE_ENTRY_CTLS:
> -               ctl_high &= ~VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL;
> +               ctl_high &= ~EVMCS1_UNSUPPORTED_VMENTRY_CTRL;
>                 break;
>         case MSR_IA32_VMX_PROCBASED_CTLS2:
>                 ctl_high &= ~SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
> 
> to be on the safe side.

Yes, it looks good to me, will add it to new patch, thanks!

> 
> -- 
> Vitaly