Re: [RFC PATCH v2 09/18] KVM: TDX: Avoid a double-KVM_BUG_ON() in tdx_sept_zap_private_spte()

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

On 8/29/2025 8:06 AM, Sean Christopherson wrote:
> Return -EIO immediately from tdx_sept_zap_private_spte() if the number of
> to-be-added pages underflows, so that the following "KVM_BUG_ON(err, kvm)"
> isn't also triggered.  Isolating the check from the "is premap error"
> if-statement will also allow adding a lockdep assertion that premap errors
> are encountered if and only if slots_lock is held.
>
> Reviewed-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/kvm/vmx/tdx.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 07f9ad1fbfb6..cafd618ca43c 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1724,8 +1724,10 @@ static int tdx_sept_zap_private_spte(struct kvm *kvm, gfn_t gfn,
>   		err = tdh_mem_range_block(&kvm_tdx->td, gpa, tdx_level, &entry, &level_state);
>   		tdx_no_vcpus_enter_stop(kvm);
>   	}
> -	if (tdx_is_sept_zap_err_due_to_premap(kvm_tdx, err, entry, level) &&
> -	    !KVM_BUG_ON(!atomic64_read(&kvm_tdx->nr_premapped), kvm)) {
> +	if (tdx_is_sept_zap_err_due_to_premap(kvm_tdx, err, entry, level)) {
> +		if (KVM_BUG_ON(!atomic64_read(&kvm_tdx->nr_premapped), kvm))
> +			return -EIO;
> +
>   		atomic64_dec(&kvm_tdx->nr_premapped);
>   		return 0;
>   	}