linux-kernel - Re: [PATCH 10/16] KVM: x86/tdp_mmu: Support TDX private mapping for TDP MMU

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Date: Wed, 29 May 2024 01:50:05 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "Yamahata, Isaku" <isaku.yamahata@...el.com>
CC: "dmatlack@...gle.com" <dmatlack@...gle.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "sagis@...gle.com" <sagis@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Zhao, Yan Y"
	<yan.y.zhao@...el.com>, "Aktas, Erdem" <erdemaktas@...gle.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>
Subject: Re: [PATCH 10/16] KVM: x86/tdp_mmu: Support TDX private mapping for
 TDP MMU

On Tue, 2024-05-28 at 18:16 -0700, Isaku Yamahata wrote:
> > Looking at how to create some more explainable code here, I'm also wondering
> > about the tdx_track() call in tdx_sept_remove_private_spte(). I didn't
> > realize
> > it will send IPIs to each vcpu for *each* page getting zapped. Another one
> > in
> > the "to optimize later" bucket I guess. And I guess it won't happen very
> > often.
> 
> We need it. Without tracking (or TLB shoot down), we'll hit
> TDX_TLB_TRACKING_NOT_DONE.  The TDX module has to guarantee that there is no
> remaining TLB entries for pages freed by TDH.MEM.PAGE.REMOVE().

It can't be removed without other changes, but the TDX module doesn't enforce
that you have to zap and shootdown a page at at time, right? Like it could be
batched.