linux-kernel - Re: [RFC PATCH 06/12] KVM: TDX: Return -EIO, not -EINVAL, on a KVM_BUG

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Message-ID: <11edfb8db22a48d2fe1c7a871f50fc07b77494d8.camel@intel.com>
Date: Thu, 28 Aug 2025 02:11:52 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "pbonzini@...hat.com" <pbonzini@...hat.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "Annapurve, Vishal"
	<vannapurve@...gle.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Zhao, Yan Y" <yan.y.zhao@...el.com>,
	"michael.roth@....com" <michael.roth@....com>, "Weiny, Ira"
	<ira.weiny@...el.com>
Subject: Re: [RFC PATCH 06/12] KVM: TDX: Return -EIO, not -EINVAL, on a
 KVM_BUG_ON() condition

On Tue, 2025-08-26 at 17:05 -0700, Sean Christopherson wrote:
> Return -EIO when a KVM_BUG_ON() is tripped, as KVM's ABI is to return -EIO
> when a VM has been killed due to a KVM bug, not -EINVAL.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/vmx/tdx.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 9fb6e5f02cc9..ef4ffcad131f 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1624,7 +1624,7 @@ static int tdx_mem_page_record_premap_cnt(struct kvm *kvm, gfn_t gfn,
>  	struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
>  
>  	if (KVM_BUG_ON(kvm->arch.pre_fault_allowed, kvm))
> -		return -EINVAL;
> +		return -EIO;
>  
>  	/* nr_premapped will be decreased when tdh_mem_page_add() is called. */
>  	atomic64_inc(&kvm_tdx->nr_premapped);
> @@ -1638,7 +1638,7 @@ static int tdx_sept_set_private_spte(struct kvm *kvm, gfn_t gfn,
>  
>  	/* TODO: handle large pages. */
>  	if (KVM_BUG_ON(level != PG_LEVEL_4K, kvm))
> -		return -EINVAL;
> +		return -EIO;
>  
>  	/*
>  	 * Read 'pre_fault_allowed' before 'kvm_tdx->state'; see matching
> @@ -1849,7 +1849,7 @@ static int tdx_sept_free_private_spt(struct kvm *kvm, gfn_t gfn,
>  	 * and slot move/deletion.
>  	 */
>  	if (KVM_BUG_ON(is_hkid_assigned(kvm_tdx), kvm))
> -		return -EINVAL;
> +		return -EIO;
>  
>  	/*
>  	 * The HKID assigned to this TD was already freed and cache was
> @@ -1870,7 +1870,7 @@ static int tdx_sept_remove_private_spte(struct kvm *kvm, gfn_t gfn,
>  	 * there can't be anything populated in the private EPT.
>  	 */
>  	if (KVM_BUG_ON(!is_hkid_assigned(to_kvm_tdx(kvm)), kvm))
> -		return -EINVAL;
> +		return -EIO;
>  
>  	ret = tdx_sept_zap_private_spte(kvm, gfn, level, page);
>  	if (ret <= 0)


Did you miss?
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index f9ac590e8ff0..fd1b8fea55a9 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1656,10 +1656,10 @@ static int tdx_sept_drop_private_spte(struct kvm *kvm,
gfn_t gfn,
 
        /* TODO: handle large pages. */
        if (KVM_BUG_ON(level != PG_LEVEL_4K, kvm))
-               return -EINVAL;
+               return -EIO;
 
        if (KVM_BUG_ON(!is_hkid_assigned(kvm_tdx), kvm))
-               return -EINVAL;
+               return -EIO;
 
        /*
         * When zapping private page, write lock is held. So no race condition


We really have a lot of KVM_BUG_ON()s in tdx code. I hesitate to pull them out
but it feels a bit gratuitous.