linux-kernel - Re: [RFC PATCH v5 058/104] KVM: x86/mmu: Focibly use TDP MMU for TDX

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Message-ID: <a975acec7aba5ee383a7112ecd45f51bb2665323.camel@intel.com>
Date:   Thu, 07 Apr 2022 13:49:41 +1200
From:   Kai Huang <kai.huang@...el.com>
To:     isaku.yamahata@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>, erdemaktas@...gle.com,
        Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v5 058/104] KVM: x86/mmu: Focibly use TDP MMU for TDX

On Fri, 2022-03-04 at 11:49 -0800, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> At this point, TDX supports TDP MMU and doesn't support legacy MMU.
> Forcibly use TDP MMU for TDX irrelevant of kernel parameter to disable
> TDP MMU.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>  arch/x86/kvm/mmu/tdp_mmu.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index b33ace3d4456..9df6aa4da202 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -16,7 +16,12 @@ module_param_named(tdp_mmu, tdp_mmu_enabled, bool, 0644);
>  /* Initializes the TDP MMU for the VM, if enabled. */
>  bool kvm_mmu_init_tdp_mmu(struct kvm *kvm)
>  {
> -	if (!tdp_enabled || !READ_ONCE(tdp_mmu_enabled))
> +	/*
> +	 *  Because TDX supports only TDP MMU, forcibly use TDP MMU in the case
> +	 *  of TDX.
> +	 */
> +	if (kvm->arch.vm_type != KVM_X86_TDX_VM &&
> +		(!tdp_enabled || !READ_ONCE(tdp_mmu_enabled)))
>  		return false;
>  
>  	/* This should not be changed for the lifetime of the VM. */

Please move this patch forward before introducing any private/shared mapping
support, otherwise nothing prevents you from creating a TD against legacy MMU,
which is broken (especially you have allowed userspace to create TD in patch 10
"KVM: TDX: Make TDX VM type supported").

-- 
Thanks,
-Kai