linux-kernel - Re: [PATCH 5/7] KVM: nVMX: Reset eVMCS clean fields data from prepare

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Message-ID: <YJqxmJg0HajlfDa/@google.com>
Date:   Tue, 11 May 2021 16:32:24 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        linux-kernel@...r.kernel.org, Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: Re: [PATCH 5/7] KVM: nVMX: Reset eVMCS clean fields data from
 prepare_vmcs02()

On Tue, May 11, 2021, Vitaly Kuznetsov wrote:
> When nested state migration happens during L1's execution, it
> is incorrect to modify eVMCS as it is L1 who 'owns' it at the moment.
> At lease genuine Hyper-v seems to not be very happy when 'clean fields'
> data changes underneath it.
> 
> 'Clean fields' data is used in KVM twice: by copy_enlightened_to_vmcs12()
> and prepare_vmcs02_rare() so we can reset it from prepare_vmcs02() instead.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/vmx/nested.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 3257a2291693..1661e2e19560 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -2090,9 +2090,6 @@ void nested_sync_vmcs12_to_shadow(struct kvm_vcpu *vcpu)
>  
>  	if (vmx->nested.hv_evmcs) {
>  		copy_vmcs12_to_enlightened(vmx);
> -		/* All fields are clean */
> -		vmx->nested.hv_evmcs->hv_clean_fields |=
> -			HV_VMX_ENLIGHTENED_CLEAN_FIELD_ALL;
>  	} else {
>  		copy_vmcs12_to_shadow(vmx);
>  	}

Looks like this makes both paths single lines, i.e. the curly braces can be
dropped.

> @@ -2636,6 +2633,12 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
>  
>  	kvm_rsp_write(vcpu, vmcs12->guest_rsp);
>  	kvm_rip_write(vcpu, vmcs12->guest_rip);
> +
> +	/* Mark all fields as clean so L1 hypervisor can set what's dirty */
> +	if (hv_evmcs)
> +		vmx->nested.hv_evmcs->hv_clean_fields |=
> +			HV_VMX_ENLIGHTENED_CLEAN_FIELD_ALL;
> +
>  	return 0;
>  }
>  
> -- 
> 2.30.2
>