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

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Message-ID: <0f4225bf-92fd-48a2-8015-65da12a135c8@linux.intel.com>
Date: Fri, 29 Aug 2025 17:52:41 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, Ira Weiny <ira.weiny@...el.com>,
 Kai Huang <kai.huang@...el.com>, Michael Roth <michael.roth@....com>,
 Yan Zhao <yan.y.zhao@...el.com>, Vishal Annapurve <vannapurve@...gle.com>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>,
 Ackerley Tng <ackerleytng@...gle.com>
Subject: Re: [RFC PATCH v2 09/18] KVM: TDX: Avoid a double-KVM_BUG_ON() in
 tdx_sept_zap_private_spte()



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@...el.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Binbin Wu <binbin.wu@...ux.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;
>   	}