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Tue, 21 Jul 2026 03:28:29 -0700 (PDT) X-Received: by 2002:a05:600c:4f0e:b0:495:4f84:7280 with SMTP id 5b1f17b1804b1-4954f847354mr171614635e9.4.1784629709119; Tue, 21 Jul 2026 03:28:29 -0700 (PDT) Received: from [192.168.10.48] ([151.49.94.110]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4956537c7desm77013385e9.7.2026.07.21.03.28.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Jul 2026 03:28:28 -0700 (PDT) From: Paolo Bonzini To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Hyunwoo Kim , stable@vger.kernel.org Subject: [PATCH] KVM: nVMX: Hide shadow VMCS right after VMCLEAR Date: Tue, 21 Jul 2026 12:28:27 +0200 Message-ID: <20260721102827.313208-1-pbonzini@redhat.com> X-Mailer: git-send-email 2.55.0 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: Hyunwoo Kim free_nested() frees the shadow VMCS while vmcs01 still points to it. But because it is asynchronous with respect to loaded_vmcs_clear(), the vCPU might migrate before the pointer is cleared and __loaded_vmcs_clear() may then execute VMCLEAR. The VMCS needs to stay attached until its explicit VMCLEAR completes, but then it can be hidden and the page safely freed. Fixes: 355f4fb1405e ("kvm: nVMX: VMCLEAR an active shadow VMCS after last u= se") Cc: stable@vger.kernel.org Signed-off-by: Hyunwoo Kim Signed-off-by: Paolo Bonzini --- arch/x86/kvm/vmx/nested.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 220d42ebc82e..ddf6df7bee93 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -336,6 +336,7 @@ static void nested_put_vmcs12_pages(struct kvm_vcpu *vc= pu) static void free_nested(struct kvm_vcpu *vcpu) { struct vcpu_vmx *vmx =3D to_vmx(vcpu); + struct vmcs *shadow_vmcs; =20 if (WARN_ON_ONCE(vmx->loaded_vmcs !=3D &vmx->vmcs01)) vmx_switch_vmcs(vcpu, &vmx->vmcs01); @@ -353,9 +354,15 @@ static void free_nested(struct kvm_vcpu *vcpu) vmx->nested.current_vmptr =3D INVALID_GPA; if (enable_shadow_vmcs) { vmx_disable_shadow_vmcs(vmx); - vmcs_clear(vmx->vmcs01.shadow_vmcs); - free_vmcs(vmx->vmcs01.shadow_vmcs); + + /* + * Keep the pointer visible until after VMCLEAR, so migration + * can clear an active shadow VMCS on the old CPU. + */ + shadow_vmcs =3D vmx->vmcs01.shadow_vmcs; + vmcs_clear(shadow_vmcs); vmx->vmcs01.shadow_vmcs =3D NULL; + free_vmcs(shadow_vmcs); } kfree(vmx->nested.cached_vmcs12); vmx->nested.cached_vmcs12 =3D NULL; --=20 2.55.0