linux-kernel - Re: [PATCH v2] KVM: nVMX: Fix nested bus lock VM exit

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Date:   Wed, 22 Sep 2021 10:00:27 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Chenyi Qiang <chenyi.qiang@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM: nVMX: Fix nested bus lock VM exit

On 9/14/2021 5:50 PM, Chenyi Qiang wrote:
> Nested bus lock VM exits are not supported yet. If L2 triggers bus lock
> VM exit, it will be directed to L1 VMM, which would cause unexpected
> behavior. Therefore, handle L2's bus lock VM exits in L0 directly.
> 
> Fixes: fe6b6bc802b4 ("KVM: VMX: Enable bus lock VM exit")
> Signed-off-by: Chenyi Qiang <chenyi.qiang@...el.com>

Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>

> ---
> Change log
> v1->v2
> - Because nested bus lock VM exit is not supported and how nested
>    support would operate is uncertain. Add a brief comment to state that this
>    feature is never exposed to L1 at present. (Sean)
> - v1: https://lore.kernel.org/lkml/20210827085110.6763-1-chenyi.qiang@intel.com/
> ---
>   arch/x86/kvm/vmx/nested.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index bc6327950657..5646cc1e8d4c 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -5873,6 +5873,12 @@ static bool nested_vmx_l0_wants_exit(struct kvm_vcpu *vcpu,
>   	case EXIT_REASON_VMFUNC:
>   		/* VM functions are emulated through L2->L0 vmexits. */
>   		return true;
> +	case EXIT_REASON_BUS_LOCK:
> +		/*
> +		 * At present, bus lock VM exit is never exposed to L1.
> +		 * Handle L2's bus locks in L0 directly.
> +		 */
> +		return true;
>   	default:
>   		break;
>   	}
>