linux-kernel - Re: [PATCH v3 04/10] KVM: nVMX: Switch to vmcs01 to update PML controls on-demand if L2 is active

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Message-ID: <aUucAR7QBjVTC2jT@intel.com>
Date: Wed, 24 Dec 2025 15:53:37 +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 04/10] KVM: nVMX: Switch to vmcs01 to update PML
 controls on-demand if L2 is active

On Fri, Dec 05, 2025 at 03:19:07PM -0800, Sean Christopherson wrote:
>If KVM toggles "CPU dirty logging", a.k.a. Page-Modification Logging (PML),
>while L2 is active, temporarily load vmcs01 and immediately update the
>relevant controls instead of deferring the update until the next nested
>VM-Exit.  For PML, deferring the 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.
>
>Convert PML first precisely because it's the simplest case to handle: if
>something is broken with the vmcs01 <=> vmcs02 dance, then hopefully bugs
>will bisect here.
>
>Signed-off-by: Sean Christopherson <seanjc@...gle.com>

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