linux-kernel - Re: [PATCH v4 12/28] KVM: TDX: WARN if mirror SPTE doesn't have full RWX when creating S-EPT mapping

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Message-ID: <6572689b28a76bd95bc653b1fc1131fa57ed7669.camel@intel.com>
Date: Thu, 30 Oct 2025 22:59:07 +0000
From: "Huang, Kai" <kai.huang@...el.com>
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Subject: Re: [PATCH v4 12/28] KVM: TDX: WARN if mirror SPTE doesn't have full
 RWX when creating S-EPT mapping

On Thu, 2025-10-30 at 13:09 -0700, Sean Christopherson wrote:
> Pass in the mirror_spte to kvm_x86_ops.set_external_spte() to provide
> symmetry with .remove_external_spte(), and assert in TDX that the mirror
> SPTE is shadow-present with full RWX permissions (the TDX-Module doesn't
> allow the hypervisor to control protections).
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Kai Huang <kai.huang@...el.com>

[...]

>  static int tdx_sept_set_private_spte(struct kvm *kvm, gfn_t gfn,
> -				     enum pg_level level, kvm_pfn_t pfn)
> +				     enum pg_level level, u64 mirror_spte)
>  {
>  	struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> +	kvm_pfn_t pfn = spte_to_pfn(mirror_spte);
>  
>  	/* TODO: handle large pages. */
>  	if (KVM_BUG_ON(level != PG_LEVEL_4K, kvm))
>  		return -EIO;
>  
> +	WARN_ON_ONCE(!is_shadow_present_pte(mirror_spte) ||
> +		     (mirror_spte & VMX_EPT_RWX_MASK) != VMX_EPT_RWX_MASK);
> +

Nit: 

I am a little bit confused about when to use WARN_ON_ONCE() and
KVM_BUG_ON(). :-)