linux-kernel - Re: [PATCH v19 052/130] KVM: x86/mmu: Track shadow MMIO value on a per-VM basis

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Date: Tue, 26 Mar 2024 03:31:05 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Yamahata,
 Isaku" <isaku.yamahata@...el.com>
CC: "Zhang, Tina" <tina.zhang@...el.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "Yuan, Hang" <hang.yuan@...el.com>, "Huang, Kai"
	<kai.huang@...el.com>, "Chen, Bo2" <chen.bo@...el.com>, "sagis@...gle.com"
	<sagis@...gle.com>, "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
	"Aktas, Erdem" <erdemaktas@...gle.com>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "sean.j.christopherson@...el.com"
	<sean.j.christopherson@...el.com>
Subject: Re: [PATCH v19 052/130] KVM: x86/mmu: Track shadow MMIO value on a
 per-VM basis

On Mon, 2024-02-26 at 00:25 -0800, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> TDX will use a different shadow PTE entry value for MMIO from VMX.  Add
> members to kvm_arch and track value for MMIO per-VM instead of global
> variables.  By using the per-VM EPT entry value for MMIO, the existing VMX
> logic is kept working.  Introduce a separate setter function so that guest
> TD can override later.
> 
> Also require mmio spte caching for TDX.


> Actually this is true case
> because TDX requires EPT and KVM EPT allows mmio spte caching.
> 

I can't understand what this is trying to say.

>  
>  void kvm_mmu_init_vm(struct kvm *kvm)
>  {
> +
> +       kvm->arch.shadow_mmio_value = shadow_mmio_value;

It could use kvm_mmu_set_mmio_spte_value()?

>         INIT_LIST_HEAD(&kvm->arch.active_mmu_pages);