linux-kernel - Re: [PATCH v11 039/113] KVM: x86/mmu: Require TDP MMU for TDX

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Message-ID: <6e7d04537f65a7ea6597e8e1ecda87fe1bb9b546.camel@intel.com>
Date:   Thu, 19 Jan 2023 11:37:25 +0000
From:   "Huang, Kai" <kai.huang@...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:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "Aktas, Erdem" <erdemaktas@...gle.com>,
        "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
        "dmatlack@...gle.com" <dmatlack@...gle.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>
Subject: Re: [PATCH v11 039/113] KVM: x86/mmu: Require TDP MMU for TDX

On Thu, 2023-01-12 at 08:31 -0800, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> Require the TDP MMU for guest TDs, the so called "shadow" MMU does not
> support mapping guest private memory, i.e. does not support Secure-EPT.

It's not accurate.  Legacy MMU using EPT can also support.  We just choose to
not support.  Please revisit.

> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>  arch/x86/kvm/mmu/tdp_mmu.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index fdcff390ebc2..6c3ce4121a46 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -27,6 +27,13 @@ int kvm_mmu_init_tdp_mmu(struct kvm *kvm)
>  	if (kvm->arch.vm_type == KVM_X86_TDX_VM && !enable_mmio_caching)
>  		return -EOPNOTSUPP;
>  
> +	/*
> +	 * Because only the TDP MMU supports TDX, require the TDP MMU for guest
> +	 * TDs.
> +	 */
> +	if (kvm->arch.vm_type == KVM_X86_TDX_VM && !tdp_enabled)
> +		return -EOPNOTSUPP;
> +
>  	if (!tdp_enabled || !READ_ONCE(tdp_mmu_enabled))
>  		return 0;
>