linux-kernel - Re: [PATCH 1/3] KVM: nVMX: extract calculation of the L1's EFER

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Date:   Wed, 10 Nov 2021 15:43:55 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     Wanpeng Li <wanpengli@...cent.com>, Borislav Petkov <bp@...en8.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        Sean Christopherson <seanjc@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: Re: [PATCH 1/3] KVM: nVMX: extract calculation of the L1's EFER

Maxim Levitsky <mlevitsk@...hat.com> writes:

> This will be useful in the next patch.

Nitpick: "the next patch" may not be what you expect after merge/when
backporting/... so it's better to call things out explicityly, something
like:

"The newly introduced nested_vmx_get_vmcs12_host_efer() helper will be
used when nested state is restored in vmx_set_nested_state()".

>
> No functional change intended.
>
> Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
> ---
>  arch/x86/kvm/vmx/nested.c | 22 ++++++++++++++++------
>  1 file changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index b4ee5e9f9e201..49ae96c0cc4d1 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -4228,6 +4228,21 @@ static void prepare_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
>  	kvm_clear_interrupt_queue(vcpu);
>  }
>  
> +/*
> + * Given vmcs12, return the expected L1 value of IA32_EFER
> + * after VM exit from that vmcs12
> + */
> +static inline u64 nested_vmx_get_vmcs12_host_efer(struct kvm_vcpu *vcpu,
> +						  struct vmcs12 *vmcs12)
> +{
> +	if (vmcs12->vm_exit_controls & VM_EXIT_LOAD_IA32_EFER)
> +		return vmcs12->host_ia32_efer;
> +	else if (vmcs12->vm_exit_controls & VM_EXIT_HOST_ADDR_SPACE_SIZE)
> +		return vcpu->arch.efer | (EFER_LMA | EFER_LME);
> +	else
> +		return vcpu->arch.efer & ~(EFER_LMA | EFER_LME);
> +}
> +
>  /*
>   * A part of what we need to when the nested L2 guest exits and we want to
>   * run its L1 parent, is to reset L1's guest state to the host state specified
> @@ -4243,12 +4258,7 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
>  	enum vm_entry_failure_code ignored;
>  	struct kvm_segment seg;
>  
> -	if (vmcs12->vm_exit_controls & VM_EXIT_LOAD_IA32_EFER)
> -		vcpu->arch.efer = vmcs12->host_ia32_efer;
> -	else if (vmcs12->vm_exit_controls & VM_EXIT_HOST_ADDR_SPACE_SIZE)
> -		vcpu->arch.efer |= (EFER_LMA | EFER_LME);
> -	else
> -		vcpu->arch.efer &= ~(EFER_LMA | EFER_LME);
> +	vcpu->arch.efer = nested_vmx_get_vmcs12_host_efer(vcpu, vmcs12);
>  	vmx_set_efer(vcpu, vcpu->arch.efer);
>  
>  	kvm_rsp_write(vcpu, vmcs12->host_rsp);

-- 
Vitaly