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[93.44.53.42]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-487270ea64esm77961935e9.5.2026.03.29.09.23.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 29 Mar 2026 09:23:01 -0700 (PDT) From: Paolo Bonzini To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Sean Christopherson , Alexander Bulekov , Fred Griffoul , stable@vger.kernel.org Subject: [PATCH] KVM: x86/mmu: Only WARN in direct MMUs when overwriting shadow-present SPTE Date: Sun, 29 Mar 2026 18:22:57 +0200 Message-ID: <20260329162258.106549-2-pbonzini@redhat.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Sean Christopherson Adjust KVM's sanity check against overwriting a shadow-present SPTE with a another SPTE with a different target PFN to only apply to direct MMUs, i.e. only to MMUs without shadowed gPTEs. While it's impossible for KVM to overwrite a shadow-present SPTE in response to a guest write, writes from outside the scope of KVM, e.g. from host userspace, aren't detected by KVM's write tracking and so can break KVM's shadow paging rules. ------------[ cut here ]------------ pfn !=3D spte_to_pfn(*sptep) WARNING: arch/x86/kvm/mmu/mmu.c:3069 at mmu_set_spte+0x1e4/0x440 [kvm], C= PU#0: vmx_ept_stale_r/872 Modules linked in: kvm_intel kvm irqbypass CPU: 0 UID: 1000 PID: 872 Comm: vmx_ept_stale_r Not tainted 7.0.0-rc2-eaf= ebd2d2ab0-sink-vm #319 PREEMPT Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:mmu_set_spte+0x1e4/0x440 [kvm] Call Trace: ept_page_fault+0x535/0x7f0 [kvm] kvm_mmu_do_page_fault+0xee/0x1f0 [kvm] kvm_mmu_page_fault+0x8d/0x620 [kvm] vmx_handle_exit+0x18c/0x5a0 [kvm_intel] kvm_arch_vcpu_ioctl_run+0xc55/0x1c20 [kvm] kvm_vcpu_ioctl+0x2d5/0x980 [kvm] __x64_sys_ioctl+0x8a/0xd0 do_syscall_64+0xb5/0x730 entry_SYSCALL_64_after_hwframe+0x4b/0x53 ---[ end trace 0000000000000000 ]--- Fixes: 11d45175111d ("KVM: x86/mmu: Warn if PFN changes on shadow-present S= PTE in shadow MMU") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson --- arch/x86/kvm/mmu/mmu.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 98406d6aa2d6..dd06453d5b72 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -3060,7 +3060,8 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, struct= kvm_memory_slot *slot, child =3D spte_to_child_sp(pte); drop_parent_pte(vcpu->kvm, child, sptep); flush =3D true; - } else if (WARN_ON_ONCE(pfn !=3D spte_to_pfn(*sptep))) { + } else if (pfn !=3D spte_to_pfn(*sptep)) { + WARN_ON_ONCE(vcpu->arch.mmu->root_role.direct); drop_spte(vcpu->kvm, sptep); flush =3D true; } else --=20 2.53.0