Re: [PATCH 6.1.y] KVM: nVMX: Immediately refresh APICv controls as needed on nested VM-Exit

[Sean Christopherson <seanjc@google.com>]

On Wed, Dec 31, 2025, Sasha Levin wrote:
> From: Dongli Zhang <dongli.zhang@oracle.com>
> 
> [ Upstream commit 29763138830916f46daaa50e83e7f4f907a3236b ]
> 
> If an APICv status updated was pended while L2 was active, immediately
> refresh vmcs01's controls instead of pending KVM_REQ_APICV_UPDATE as
> kvm_vcpu_update_apicv() only calls into vendor code if a change is
> necessary.
> 
> E.g. if APICv is inhibited, and then activated while L2 is running:
> 
>   kvm_vcpu_update_apicv()
>   |
>   -> __kvm_vcpu_update_apicv()
>      |
>      -> apic->apicv_active = true
>       |
>       -> vmx_refresh_apicv_exec_ctrl()
>          |
>          -> vmx->nested.update_vmcs01_apicv_status = true
>           |
>           -> return
> 
> Then L2 exits to L1:
> 
>   __nested_vmx_vmexit()
>   |
>   -> kvm_make_request(KVM_REQ_APICV_UPDATE)
> 
>   vcpu_enter_guest(): KVM_REQ_APICV_UPDATE
>   -> kvm_vcpu_update_apicv()
>      |
>      -> __kvm_vcpu_update_apicv()
>         |
>         -> return // because if (apic->apicv_active == activate)
> 
> Reported-by: Chao Gao <chao.gao@intel.com>
> Closes: https://lore.kernel.org/all/aQ2jmnN8wUYVEawF@intel.com
> Fixes: 7c69661e225c ("KVM: nVMX: Defer APICv updates while L2 is active until L1 is active")
> Cc: stable@vger.kernel.org
> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> [sean: write changelog]
> Link: https://patch.msgid.link/20251205231913.441872-3-seanjc@google.com
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> [ exported vmx_refresh_apicv_exec_ctrl() and added declaration in vmx.h ]
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---

Acked-by: Sean Christopherson <seanjc@google.com>