linux-kernel - Re: [PATCH v3 3/3] KVM: nVMX: Add CET entry/exit load bits to evmcs unsupported list

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Date:   Thu, 04 Mar 2021 10:52:04 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Yang Weijiang <weijiang.yang@...el.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 v3 3/3] KVM: nVMX: Add CET entry/exit load bits to evmcs
 unsupported list

Yang Weijiang <weijiang.yang@...el.com> writes:

> Nested guest doesn't support CET when KVM is running as an intermediate
> layer between two Hyper-Vs for now, so mask out related CET entry/exit
> load bits. Relevant enabling patches will be posted as a separate patch
> series.
>
> Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
> Suggested-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> ---
>  arch/x86/kvm/vmx/evmcs.c | 4 ++--
>  arch/x86/kvm/vmx/evmcs.h | 6 ++++--
>  2 files changed, 6 insertions(+), 4 deletions(-)
>
> 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;
> 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)

Thanks, this should be enough for both KVM on Hyper-V and Hyper-V on KVM
using eVMCS.

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly