linux-kernel - Re: [PATCH v3 11/25] KVM: VMX: Get rid of eVMCS specific VMX controls sanitization

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Date:   Tue, 12 Jul 2022 14:54:34 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 11/25] KVM: VMX: Get rid of eVMCS specific VMX
 controls sanitization

On Fri, 2022-07-08 at 16:42 +0200, Vitaly Kuznetsov wrote:
> With the updated eVMCSv1 definition, there's no known 'problematic'
> controls which are exposed in VMX control MSRs but are not present in
> eVMCSv1. Get rid of VMX control MSRs filtering for KVM on Hyper-V.

If I understand correctly we are taking about running KVM as a nested guest of Hyper-V here:

Don't we need to check the new CPUID bit and only then use the new fields of eVMCS,
aka check that the 'cpu' supports the updated eVMCS version?

Best regards,
	Maxim Levitsky



> 
> Note: VMX control MSRs filtering for Hyper-V on KVM
> (nested_evmcs_filter_control_msr()) stays as even the updated eVMCSv1
> definition doesn't have all the features implemented by KVM and some
> fields are still missing. Moreover, nested_evmcs_filter_control_msr()
> has to support the original eVMCSv1 version when VMM wishes so.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/vmx/evmcs.c | 13 -------------
>  arch/x86/kvm/vmx/evmcs.h |  1 -
>  arch/x86/kvm/vmx/vmx.c   |  5 -----
>  3 files changed, 19 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/evmcs.c b/arch/x86/kvm/vmx/evmcs.c
> index 52a53debd806..b5cfbf7d487b 100644
> --- a/arch/x86/kvm/vmx/evmcs.c
> +++ b/arch/x86/kvm/vmx/evmcs.c
> @@ -320,19 +320,6 @@ const struct evmcs_field vmcs_field_to_evmcs_1[] = {
>  };
>  const unsigned int nr_evmcs_1_fields = ARRAY_SIZE(vmcs_field_to_evmcs_1);
>  
> -#if IS_ENABLED(CONFIG_HYPERV)
> -__init void evmcs_sanitize_exec_ctrls(struct vmcs_config *vmcs_conf)
> -{
> -       vmcs_conf->cpu_based_exec_ctrl &= ~EVMCS1_UNSUPPORTED_EXEC_CTRL;
> -       vmcs_conf->pin_based_exec_ctrl &= ~EVMCS1_UNSUPPORTED_PINCTRL;
> -       vmcs_conf->cpu_based_2nd_exec_ctrl &= ~EVMCS1_UNSUPPORTED_2NDEXEC;
> -       vmcs_conf->cpu_based_3rd_exec_ctrl = 0;
> -
> -       vmcs_conf->vmexit_ctrl &= ~EVMCS1_UNSUPPORTED_VMEXIT_CTRL;
> -       vmcs_conf->vmentry_ctrl &= ~EVMCS1_UNSUPPORTED_VMENTRY_CTRL;
> -}
> -#endif
> -
>  bool nested_enlightened_vmentry(struct kvm_vcpu *vcpu, u64 *evmcs_gpa)
>  {
>         struct hv_vp_assist_page assist_page;
> diff --git a/arch/x86/kvm/vmx/evmcs.h b/arch/x86/kvm/vmx/evmcs.h
> index 4b809c79ae63..0feac101cce4 100644
> --- a/arch/x86/kvm/vmx/evmcs.h
> +++ b/arch/x86/kvm/vmx/evmcs.h
> @@ -203,7 +203,6 @@ static inline void evmcs_load(u64 phys_addr)
>         vp_ap->enlighten_vmentry = 1;
>  }
>  
> -__init void evmcs_sanitize_exec_ctrls(struct vmcs_config *vmcs_conf);
>  #else /* !IS_ENABLED(CONFIG_HYPERV) */
>  static __always_inline void evmcs_write64(unsigned long field, u64 value) {}
>  static inline void evmcs_write32(unsigned long field, u32 value) {}
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index b4915d841357..dd905ad72637 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2689,11 +2689,6 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>         vmcs_conf->vmexit_ctrl         = _vmexit_control;
>         vmcs_conf->vmentry_ctrl        = _vmentry_control;
>  
> -#if IS_ENABLED(CONFIG_HYPERV)
> -       if (enlightened_vmcs)
> -               evmcs_sanitize_exec_ctrls(vmcs_conf);
> -#endif
> -
>         return 0;
>  }
>