linux-kernel - Re: [PATCH v3 3/4] KVM: nVMX: Disallow access to vmcs12 fields that aren't supported by "hardware"

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Message-ID: <288eaa68-7d4d-4c1b-ae70-419554d1d8f2@intel.com>
Date: Fri, 9 Jan 2026 22:08:59 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Chao Gao <chao.gao@...el.com>, Xin Li <xin@...or.com>,
 Yosry Ahmed <yosry.ahmed@...ux.dev>
Subject: Re: [PATCH v3 3/4] KVM: nVMX: Disallow access to vmcs12 fields that
 aren't supported by "hardware"

On 1/9/2026 12:15 PM, Sean Christopherson wrote:
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 61113ead3d7b..ac7a17560c8f 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -111,6 +111,9 @@ static void init_vmcs_shadow_fields(void)
>   			  field <= GUEST_TR_AR_BYTES,
>   			  "Update vmcs12_write_any() to drop reserved bits from AR_BYTES");
>   
> +		if (get_vmcs12_field_offset(field) < 0)
> +			continue;
> +

why shadow_read_only_fields[] doesn't need such guard?

IIUC, copy_vmcs12_to_shadow() will VMWRITE shadowed readonly field even 
if it doesn't exist on the hardware?