linux-kernel - Re: [PATCH v3 05/10] KVM: nVMX: Switch to vmcs01 to update TPR threshold on-demand if L2 is active

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Message-ID: <aUzbz5u/PHxU09/K@intel.com>
Date: Thu, 25 Dec 2025 14:38:07 +0800
From: Chao Gao <chao.gao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: Paolo Bonzini <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Dongli Zhang <dongli.zhang@...cle.com>
Subject: Re: [PATCH v3 05/10] KVM: nVMX: Switch to vmcs01 to update TPR
 threshold on-demand if L2 is active

On Fri, Dec 05, 2025 at 03:19:08PM -0800, Sean Christopherson wrote:
>If KVM updates L1's TPR Threshold while L2 is active, temporarily load
>vmcs01 and immediately update TPR_THRESHOLD instead of deferring the
>update until the next nested VM-Exit.  Deferring the TPR Threshold update
>is relatively straightforward, but for several APICv related updates,
>deferring updates creates ordering and state consistency problems, e.g.
>KVM at-large thinks APICv is enabled, but vmcs01 is still running with
>stale (and effectively unknown) state.
>
>Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Chao Gao <chao.gao@...el.com>