linux-kernel - [PATCH v4 13/28] KVM: TDX: Avoid a double-KVM_BUG_ON() in tdx_sept_zap_private

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Message-ID: <20251030200951.3402865-14-seanjc@google.com>
Date: Thu, 30 Oct 2025 13:09:36 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
	Tianrui Zhao <zhaotianrui@...ngson.cn>, Bibo Mao <maobibo@...ngson.cn>, 
	Huacai Chen <chenhuacai@...nel.org>, Madhavan Srinivasan <maddy@...ux.ibm.com>, 
	Anup Patel <anup@...infault.org>, Paul Walmsley <pjw@...nel.org>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Christian Borntraeger <borntraeger@...ux.ibm.com>, Janosch Frank <frankja@...ux.ibm.com>, 
	Claudio Imbrenda <imbrenda@...ux.ibm.com>, Sean Christopherson <seanjc@...gle.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, "Kirill A. Shutemov" <kas@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
	kvm@...r.kernel.org, loongarch@...ts.linux.dev, linux-mips@...r.kernel.org, 
	linuxppc-dev@...ts.ozlabs.org, kvm-riscv@...ts.infradead.org, 
	linux-riscv@...ts.infradead.org, x86@...nel.org, linux-coco@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, Ira Weiny <ira.weiny@...el.com>, 
	Kai Huang <kai.huang@...el.com>, Binbin Wu <binbin.wu@...ux.intel.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: [PATCH v4 13/28] KVM: TDX: Avoid a double-KVM_BUG_ON() in tdx_sept_zap_private_spte()

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>
Reviewed-by: Binbin Wu <binbin.wu@...ux.intel.com>
Reviewed-by: Kai Huang <kai.huang@...el.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.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 658e0407eb21..db64a9e8c6a5 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1725,8 +1725,10 @@ 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;
 	}
-- 
2.51.1.930.gacf6e81ea2-goog