Re: [PATCH v2 3/3] KVM: TDX: Ratelimit the "EPT Violation on pending acceptance page" warning

[Yan Zhao <yan.y.zhao@intel.com>]

On Thu, Oct 08, 2026 at 04:04:06PM +0800, Binbin Wu wrote:
> On 10/8/2026 11:08 AM, Yan Zhao wrote:
> > On Tue, Sep 29, 2026 at 05:11:27PM -0700, Sean Christopherson wrote:
> >> Ratelimit TDX's kernel logging when a guest accesses an unaccepted page and
> >> has opted to disable EPT Violation #VEs for unaccepted accesses, as the
> >> pr_warn() is trivial for a misbehaving userspace to trigger.
> > Since the pr_warn() is previously accompanied by a kvm_vm_dead(), which kicks
> > off all vCPUs and disallows re-entry, a misbehaving guest should not be able to
> > trigger pr_warn() more than once.
> > Or are you concerned about the pr_warn() being triggered by multiple misbehaving
> > guests? But would it be better to print for each guest?
> 
> Sashiko reported the issue due to the change introduced in the patch 2.
> 
>   Will this change allow a malicious or buggy userspace VMM to flood the host
>   kernel log?
> 
>   By replacing kvm_vm_dead() with KVM_REQ_TRIPLE_FAULT and returning 1, KVM
>   will clear the request during vcpu_enter_guest() and exit to userspace with
>   KVM_EXIT_SHUTDOWN. If the VMM ignores this exit and repeatedly calls KVM_RUN
>   without resetting the vCPU, KVM will immediately re-enter the guest.
> 
> In this case, is the Fixes tag pointing to e6a85781f783 needed?
Upon further reflection, in an extreme scenario where 100 vCPUs access the
unaccepted page simultaneously, pr_warn() could theoretically be invoked for
100 times.
So pr_warn_ratelimited() is still the better choice.

So, Reviewed-by: Yan Zhao <yan.y.zhao@intel.com>
> >> Fixes: e6a85781f783 ("KVM: TDX: Detect unexpected SEPT violations due to pending SPTEs")
> >> Cc: stable@vger.kernel.org
> >> Reported-by: Sashiko Bot <sashiko-bot@kernel.org>
> >> Closes: https://lore.kernel.org/all/20260923164348.2DB2D1F000FF@smtp.kernel.org
> >> Signed-off-by: Sean Christopherson <seanjc@google.com>
> >> ---
> >>  arch/x86/kvm/vmx/tdx.c | 4 ++--
> >>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> >> index e3723f1222fc..4cac43299851 100644
> >> --- a/arch/x86/kvm/vmx/tdx.c
> >> +++ b/arch/x86/kvm/vmx/tdx.c
> >> @@ -1937,8 +1937,8 @@ static int tdx_handle_ept_violation(struct kvm_vcpu *vcpu)
> >>  
> >>  	if (vt_is_tdx_private_gpa(vcpu->kvm, gpa)) {
> >>  		if (tdx_is_sept_violation_unexpected_pending(vcpu)) {
> >> -			pr_warn("Guest access before accepting 0x%llx on vCPU %d\n",
> >> -				gpa, vcpu->vcpu_id);
> >> +			pr_warn_ratelimited("Guest access before accepting 0x%llx on vCPU %d\n",
> >> +					    gpa, vcpu->vcpu_id);
> >>  			kvm_prepare_shutdown_exit(vcpu);
> >>  			return 0;
> >>  		}
> >> -- 
> >> 2.56.0.rc1.315.gc6ed9934b7-goog
> >>
> > 
>