linux-kernel - Re: [PATCH] KVM: x86/mmu: Implement memslot deletion for TDX

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Date: Fri, 21 Jun 2024 01:17:55 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "seanjc@...gle.com" <seanjc@...gle.com>
CC: "Huang, Kai" <kai.huang@...el.com>, "sagis@...gle.com" <sagis@...gle.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>, "Yamahata, Isaku" <isaku.yamahata@...el.com>,
	"dmatlack@...gle.com" <dmatlack@...gle.com>
Subject: Re: [PATCH] KVM: x86/mmu: Implement memslot deletion for TDX

On Thu, 2024-06-20 at 17:08 -0700, Sean Christopherson wrote:
> On Thu, Jun 20, 2024, Rick Edgecombe wrote:
> > Force TDX VMs to use the KVM_X86_QUIRK_SLOT_ZAP_ALL behavior.
> > 
> > TDs cannot use the fast zapping operation to implement memslot deletion for
> > a couple reasons:
> > 1. KVM cannot zap TDX private PTEs and re-fault them without coordinating
> 
> Uber nit, this isn't strictly true, for KVM's definition of "zap" (which is
> fuzzy
> and overloaded).  KVM _could_ zap and re-fault *leaf* PTEs, e.g.
> BLOCK+UNBLOCK.
> It's specifically the full teardown and rebuild of the "fast zap" that doesn't
> play nice, as the non-leaf S-EPT entries *must* be preserved due to how the
> TDX
> module does is refcounting.

Hmm, yea. That is probably worth an update. I'll change it for when I post
another version of this patch.

I was imaging this series might go up ahead of the rest of the MMU prep stuff.
In which case I can just post a new version of this patch on top of kvm-coco-
queue once this series appears in the base of that branch. Assuming there is no
problems with that, I won't post a v2 right away.