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 02:29:26 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "Yamahata, Isaku" <isaku.yamahata@...el.com>
CC: "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "sagis@...gle.com" <sagis@...gle.com>,
	"isaku.yamahata@...ux.intel.com" <isaku.yamahata@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Aktas, Erdem"
	<erdemaktas@...gle.com>, "Zhao, Yan Y" <yan.y.zhao@...el.com>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "dmatlack@...gle.com" <dmatlack@...gle.com>
Subject: Re: [PATCH 10/16] KVM: x86/tdp_mmu: Support TDX private mapping for
 TDP MMU

On Tue, 2024-05-28 at 19:20 -0700, Isaku Yamahata wrote:
> Right. TDX module doesn't enforce it.  If we want to batch zapping, it
> requires
> to track the SPTE state, zapped, not TLB shoot down yet, and not removed yet.
> It's simpler to issue TLB shoot per page for now. It would be future
> optimization.

Totally agree we should not change it now. It's just in the list of not
optimized things.

> 
> At runtime, the zapping happens when memory conversion(private -> shared) or
> memslot deletion.  Because it's not often, we don't have to care.

Not sure I agree on this part. But in any case we can discuss it when we are in
the happy situation of upstream TDX users existing and complaining about things.

A great thing about it though - it's obviously correct.

> For vm destruction, it's simpler to skip tlb shoot down by deleting HKID first
> than to track SPTE state for batching TLB shoot down.