linux-kernel - Re: [PATCH v2 2/2] KVM: TDX: WARN if a SEAMCALL VM-Exit makes its way out to KVM

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Message-ID: <46eb76240a29cb81b6a8aa41016466810abef559.camel@intel.com>
Date: Fri, 17 Oct 2025 10:40:50 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "pbonzini@...hat.com" <pbonzini@...hat.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>
CC: "Li, Xiaoyao" <xiaoyao.li@...el.com>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "Williams, Dan J" <dan.j.williams@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Edgecombe,
 Rick P" <rick.p.edgecombe@...el.com>, "binbin.wu@...ux.intel.com"
	<binbin.wu@...ux.intel.com>
Subject: Re: [PATCH v2 2/2] KVM: TDX: WARN if a SEAMCALL VM-Exit makes its way
 out to KVM

On Thu, 2025-10-16 at 11:21 -0700, Sean Christopherson wrote:
> WARN if KVM observes a SEAMCALL VM-Exit while running a TD guest, as the
> TDX-Module is supposed to inject a #UD, per the "Unconditionally Blocked
> Instructions" section of the TDX-Module base specification.
> 
> Reported-by: Xiaoyao Li <xiaoyao.li@...el.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/vmx/tdx.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 097304bf1e1d..ffcfe95f224f 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -2148,6 +2148,9 @@ int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
>  		 * - If it's not an MSMI, no need to do anything here.
>  		 */
>  		return 1;
> +	case EXIT_REASON_SEAMCALL:
> +		WARN_ON_ONCE(1);
> +		break;
> 

While this exit should never happen from a TDX guest, I am wondering why
we need to explicitly handle the SEAMCALL?  E.g., per "Unconditionally
Blocked Instructions" ENCLS/ENCLV are also listed, therefore
EXIT_REASON_ELCLS/ENCLV should never come from a TDX guest either.