linux-kernel - Re: [PATCH v3 16/17] KVM: x86/tdp_mmu: Propagate tearing down mirror page tables

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Date: Mon, 24 Jun 2024 23:55:00 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>
CC: "seanjc@...gle.com" <seanjc@...gle.com>, "Huang, Kai"
	<kai.huang@...el.com>, "sagis@...gle.com" <sagis@...gle.com>,
	"isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Aktas, Erdem"
	<erdemaktas@...gle.com>, "dmatlack@...gle.com" <dmatlack@...gle.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "pbonzini@...hat.com" <pbonzini@...hat.com>,
	"Zhao, Yan Y" <yan.y.zhao@...el.com>
Subject: Re: [PATCH v3 16/17] KVM: x86/tdp_mmu: Propagate tearing down mirror
 page tables

On Thu, 2024-06-20 at 16:44 +0800, Binbin Wu wrote:
> > TDX MMU support will exclude certain MMU operations, so only plug in the
> > mirroring x86 ops where they will be needed. For zapping/freeing, only
> > hook tdp_mmu_iter_set_spte() which is use used for mapping and linking
>                                          ^
>                                          extra "use"
> 
> Also, this sentence is a bit confusing about "used for mapping and linking".

Yes. Is this more clear? "...tdp_mmu_iter_set_spte(), which is use used for
setting leaf PTEs and linking non-leaf PTEs."

> 
> > PTs. Don't bother hooking tdp_mmu_set_spte_atomic() as it is only used for
> > zapping PTEs in operations unsupported by TDX: zapping collapsible PTEs and
> > kvm_mmu_zap_all_fast().
> > 
> > In previous changes to address races around concurrent populating using
> > tdp_mmu_set_spte_atomic(), a solution was introduced to temporarily set
> > REMOVED_SPTE in the mirrored page tables while performing the external
>    ^
>   FROZEN_SPTE

Oops. And agreed on the other nits. Thanks.