linux-kernel - Re: [RFC PATCH 09/21] KVM: TDX: Enable 2MB mapping size after TD is RUNNABLE

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Message-ID: <aFvDIDZ+Y3ny/WuF@yzhao56-desk.sh.intel.com>
Date: Wed, 25 Jun 2025 17:36:32 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
	"quic_eberman@...cinc.com" <quic_eberman@...cinc.com>, "Li, Xiaoyao"
	<xiaoyao.li@...el.com>, "Huang, Kai" <kai.huang@...el.com>, "Du, Fan"
	<fan.du@...el.com>, "Hansen, Dave" <dave.hansen@...el.com>,
	"david@...hat.com" <david@...hat.com>, "thomas.lendacky@....com"
	<thomas.lendacky@....com>, "vbabka@...e.cz" <vbabka@...e.cz>, "Li, Zhiquan1"
	<zhiquan1.li@...el.com>, "Shutemov, Kirill" <kirill.shutemov@...el.com>,
	"michael.roth@....com" <michael.roth@....com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "Weiny, Ira" <ira.weiny@...el.com>, "Peng, Chao P"
	<chao.p.peng@...el.com>, "pbonzini@...hat.com" <pbonzini@...hat.com>,
	"Yamahata, Isaku" <isaku.yamahata@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "binbin.wu@...ux.intel.com"
	<binbin.wu@...ux.intel.com>, "ackerleytng@...gle.com"
	<ackerleytng@...gle.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"Annapurve, Vishal" <vannapurve@...gle.com>, "tabba@...gle.com"
	<tabba@...gle.com>, "jroedel@...e.de" <jroedel@...e.de>, "Miao, Jun"
	<jun.miao@...el.com>, "pgonda@...gle.com" <pgonda@...gle.com>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [RFC PATCH 09/21] KVM: TDX: Enable 2MB mapping size after TD is
 RUNNABLE

On Wed, Jun 25, 2025 at 05:28:22PM +0800, Yan Zhao wrote:
> Write down my understanding to check if it's correct:
> 
> - when a TD is NOT configured to support KVM_LPAGE_GUEST_INHIBIT TDVMCALL, KVM
>   always maps at 4KB
> 
> - When a TD is configured to support KVM_LPAGE_GUEST_INHIBIT TDVMCALL,
Sorry, the two conditions are stale ones. No need any more.
So it's always
 
 (a)
 1. guest accepts at 4KB
 2. TDX sets KVM_LPAGE_GUEST_INHIBIT and try splitting.(with write mmu_lock)
 3. KVM maps at 4KB (with read mmu_lock)
 4. guest's 4KB accept succeeds.
 
 (b)
 1. guest accepts at 2MB.
 2. KVM maps at 4KB due to a certain reason.
 3. guest's accept 2MB fails with TDACCEPT_SIZE_MISMATCH.
 4. guest accepts at 4KB
 5. guest's 4KB accept succeeds.