Re: [RFC PATCH v2 08/18] KVM: x86/mmu: Drop the return code from kvm_x86_ops.remove_external_spte()

[Binbin Wu <binbin.wu@linux.intel.com>]

On 8/29/2025 8:06 AM, Sean Christopherson wrote:
> Drop the return code from kvm_x86_ops.remove_external_spte(), a.k.a.
> tdx_sept_remove_private_spte(), as KVM simply does a KVM_BUG_ON() failure,
> and that KVM_BUG_ON() is redundant since all error paths in TDX also do a
> KVM_BUG_ON().
>
> Opportunistically pass the spte instead of the pfn, as the API is clearly
> about removing an spte.
>
> Suggested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>

> ---
>   arch/x86/include/asm/kvm_host.h |  4 ++--
>   arch/x86/kvm/mmu/tdp_mmu.c      |  8 ++------
>   arch/x86/kvm/vmx/tdx.c          | 17 ++++++++---------
>   3 files changed, 12 insertions(+), 17 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 0d3cc0fc27af..d0a8404a6b8f 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1852,8 +1852,8 @@ struct kvm_x86_ops {
>   				 void *external_spt);
>   
>   	/* Update external page table from spte getting removed, and flush TLB. */
> -	int (*remove_external_spte)(struct kvm *kvm, gfn_t gfn, enum pg_level level,
> -				    kvm_pfn_t pfn_for_gfn);
> +	void (*remove_external_spte)(struct kvm *kvm, gfn_t gfn, enum pg_level level,
> +				     u64 spte);
>   
>   	bool (*has_wbinvd_exit)(void);
>   
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 3ea2dd64ce72..78ee085f7cbc 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -362,9 +362,6 @@ static void tdp_mmu_unlink_sp(struct kvm *kvm, struct kvm_mmu_page *sp)
>   static void remove_external_spte(struct kvm *kvm, gfn_t gfn, u64 old_spte,
>   				 int level)
>   {
> -	kvm_pfn_t old_pfn = spte_to_pfn(old_spte);
> -	int ret;
> -
>   	/*
>   	 * External (TDX) SPTEs are limited to PG_LEVEL_4K, and external
>   	 * PTs are removed in a special order, involving free_external_spt().
> @@ -377,9 +374,8 @@ static void remove_external_spte(struct kvm *kvm, gfn_t gfn, u64 old_spte,
>   
>   	/* Zapping leaf spte is allowed only when write lock is held. */
>   	lockdep_assert_held_write(&kvm->mmu_lock);
> -	/* Because write lock is held, operation should success. */
> -	ret = kvm_x86_call(remove_external_spte)(kvm, gfn, level, old_pfn);
> -	KVM_BUG_ON(ret, kvm);
> +
> +	kvm_x86_call(remove_external_spte)(kvm, gfn, level, old_spte);
>   }
>   
>   /**
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 8cb6a2627eb2..07f9ad1fbfb6 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1809,12 +1809,12 @@ static int tdx_sept_free_private_spt(struct kvm *kvm, gfn_t gfn,
>   	return tdx_reclaim_page(virt_to_page(private_spt));
>   }
>   
> -static int tdx_sept_remove_private_spte(struct kvm *kvm, gfn_t gfn,
> -					enum pg_level level, kvm_pfn_t pfn)
> +static void tdx_sept_remove_private_spte(struct kvm *kvm, gfn_t gfn,
> +					 enum pg_level level, u64 spte)
>   {
> +	struct page *page = pfn_to_page(spte_to_pfn(spte));
>   	int tdx_level = pg_level_to_tdx_sept_level(level);
>   	struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> -	struct page *page = pfn_to_page(pfn);
>   	gpa_t gpa = gfn_to_gpa(gfn);
>   	u64 err, entry, level_state;
>   	int ret;
> @@ -1825,15 +1825,15 @@ 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 -EIO;
> +		return;
>   
>   	/* TODO: handle large pages. */
>   	if (KVM_BUG_ON(level != PG_LEVEL_4K, kvm))
> -		return -EIO;
> +		return;
>   
>   	ret = tdx_sept_zap_private_spte(kvm, gfn, level, page);
>   	if (ret <= 0)
> -		return ret;
> +		return;
>   
>   	/*
>   	 * TDX requires TLB tracking before dropping private page.  Do
> @@ -1862,17 +1862,16 @@ static int tdx_sept_remove_private_spte(struct kvm *kvm, gfn_t gfn,
>   
>   	if (KVM_BUG_ON(err, kvm)) {
>   		pr_tdx_error_2(TDH_MEM_PAGE_REMOVE, err, entry, level_state);
> -		return -EIO;
> +		return;
>   	}
>   
>   	err = tdh_phymem_page_wbinvd_hkid((u16)kvm_tdx->hkid, page);
>   	if (KVM_BUG_ON(err, kvm)) {
>   		pr_tdx_error(TDH_PHYMEM_PAGE_WBINVD, err);
> -		return -EIO;
> +		return;
>   	}
>   
>   	tdx_clear_page(page);
> -	return 0;
>   }
>   
>   void tdx_deliver_interrupt(struct kvm_lapic *apic, int delivery_mode,